Flight below minimum altitude

Safety summary

What happened

On 12 August 2021, at about 0858 Central Standard Time, an Aero Commander 500-S aircraft, registered VH-LTP, departed Port Lincoln on a private flight to Adelaide, South Australia under instrument flight rules. On board were the pilot and one passenger.

During the descent in instrument meteorological conditions, when passing about 6,000 ft, the aircraft began to encounter turbulence. Following clearance to track direct to the GPS waypoint GULLY, the pilot reported having difficulties entering the area navigation (RNAV) instrument approach data into the aircraft’s touchscreen multi-function display due to turbulence. By the time the pilot had correctly entered it, the aircraft had just passed the waypoint. When the pilot then selected the ‘Direct-To’ option on the display, the autopilot commanded a sharp turn to the right, to commence an orbit to attempt to overfly the waypoint to recapture it.

On observing the aircraft’s track, the controller instructed the pilot to maintain 3,800 ft and to turn onto a heading of 360°, intending to vector the aircraft back towards the waypoint. About 90 seconds later, the controller instructed the pilot to turn onto heading 120°, which the pilot read back. When the controller tried to contact the pilot about 1 minute later, the pilot did not respond and communications were lost.

The aircraft continued on the assigned heading but began descending below its assigned altitude, which was also the minimum sector altitude. For 4 minutes, ATC, with the assistance from the pilot of a nearby aircraft, continued to attempt to contact the pilot of VH-LTP. During this time, the approach controller also issued the pilot three terrain safety alerts.

The pilot contacted the Melbourne Centre controller, who instructed the pilot to transfer back to the Adelaide Approach frequency. Upon regaining communication, the approach controller issued the pilot a terrain safety alert and instructed the pilot to climb immediately to 5,000 ft. The lowest altitude the aircraft descended to was 2,480 ft and the highest point within 5 NM of the aircraft’s track was 1,913 ft.

The aircraft then tracked to Adelaide Airport and landed without further incident.

What the ATSB found

The ATSB found that during the approach, the pilot was experiencing data entry difficulties due to turbulent conditions and inadvertently selected the incorrect radio frequency. Further, several factors including the environmental conditions, data entry difficulties and the timing of the clearance for the GULLY waypoint, likely led to the pilot experiencing a high workload. This in turn, likely affected the pilot’s situational awareness where they did not initially notice the frequency change nor the continued descent and descent below the assigned (minimum sector) altitude.

Safety message

The approach and landing phases are known periods of high workload for pilots. Pilots must continuously monitor aircraft and approach parameters, and the external environment, to ensure they maintain a stable approach profile and make appropriate decisions for a safe landing. The Flight Safety Foundation found that between 1984 and 1994, 50 per cent of controlled flight into terrain accidents were due to inadequate monitoring by the pilot. Distractions and unanticipated events can further increase a pilot’s workload leading to undetected errors and a loss of situational awareness. During high workload phases of flight, pilots should remain focused on monitoring the aircraft instruments and avoid fixating on a problem.

The investigation

The occurrence

On 12 August 2021, at about 0858 Central Standard Time,^[1] an Aero Commander 500-S aircraft, registered VH-LTP, departed Port Lincoln on a private flight to Adelaide, South Australia under instrument flight rules.^[2] On board were the pilot and one passenger.

At about 0930, the pilot made first contact with Adelaide Approach air traffic control (ATC) and was cleared to track direct to Adelaide maintaining 7,000 ft. The controller also advised the pilot to expect vectors for the area navigation Z (RNAV-Z)^[3] approach for runway 23. The aircraft was in instrument meteorological conditions (IMC).^[4]

About 14 minutes later, the controller cleared the aircraft to descend to 5,000 ft and turn left on a heading of 050°. The pilot recalled the aircraft encountering turbulence during the descent, which started when passing about 6,000 ft. At 0947, the controller cleared the pilot to descend to 3,800 ft and to turn right on a heading of 090°. The controller advised the pilot to expect a clearance shortly to navigate to GPS waypoint GULLY, which was the initial approach fix for the RNAV approach. Less than 1 minute later, when the aircraft was 6 NM north-west of GULLY, the controller cleared the pilot for the RNAV approach and instructed the pilot to track direct to GULLY (Figure 1).

The pilot began tracking to GULLY and reported having difficulties entering the RNAV approach details into the aircraft’s touchscreen multi‑function display (MFD) due to the turbulence. By the time the pilot had correctly entered it, the aircraft had just passed the GULLY waypoint and when the pilot then selected the ‘Direct-To’ option on the display, the autopilot commanded a sharp turn to the right, to orbit back around to recapture the waypoint (Figure 1).

Observing the aircraft’s track away from the waypoint, the controller, at 0951, advised the pilot they had missed the approach and instructed them to maintain 3,800 ft. They then instructed the pilot to turn right on a heading of 360° and to expect vectors back to GULLY.  After turning to the assigned heading, the aircraft started a gentle climb. At 0953, the controller instructed the pilot to turn right onto heading 120° and to expect a clearance to navigate to GULLY shortly. The pilot correctly read back the clearance and later recalled having commenced a descent, realising the aircraft was then above the assigned altitude. This was the last radio call the pilot received from the Adelaide Approach controller before the pilot inadvertently switched the radio frequency back to Melbourne Centre.^[5]

About 1 minute later, when the aircraft was 2.5 NM north of GULLY, the controller issued the expected clearance – to resume their own navigation, track direct to GULLY, descend to 3,800 ft and conduct the RNAV approach for runway 23. The controller did not receive a response from the pilot.

The pilot continued on their last assigned heading of 120° and the aircraft began descending below its assigned altitude of 3,800 ft, which was also the minimum sector altitude. For 4 minutes, ATC, with the assistance from the pilot of a nearby aircraft, continued to attempt to contact the pilot of VH-LTP. During this time, the controller also issued the pilot three terrain safety alerts.

At 0957, the pilot of VH-LTP made a radio call to ATC, which was received by the Melbourne Centre, to ask the approach controller whether they should track back to GULLY. When the pilot received no reply, they made another call. The Melbourne Centre controller responded, told the pilot to standby and then instructed them to contact Adelaide Approach on frequency 118.2. The controller then contacted the Adelaide Approach controller to inform them that they had the pilot on the Melbourne Centre frequency, and the pilot was transferring back to the correct frequency. Upon regaining communication with the pilot, the approach controller immediately issued a terrain safety alert and instructed the pilot to climb immediately to 5,000 ft. The aircraft’s altitude at that time was 2,780 ft.

After observing no increase in the aircraft’s altitude for almost 1 minute, the controller contacted the pilot and asked them to confirm climbing to 5,000 ft. The pilot confirmed and the aircraft began to climb. The lowest altitude the aircraft descended to was 2,480 ft, the highest point within 5 NM of the aircraft’s track was 1,913 ft (Figure 2).

Figure 1: VH-LTP flight path (dotted line shows RNAV instrument approach path)

Source: Google Earth overlaid with Airservices data, annotated by the ATSB

Figure 2: VH-LTP’s altitude relative to the terrain (in feet)

Source: Geoscience terrain data overlaid with Airservices data, annotated by the ATSB

The controller vectored the aircraft back to Adelaide Airport for a RNAV-Z approach for runway 05. The aircraft landed at Adelaide Airport at 1028.

Context

Pilot information

The pilot previously held a Commercial Pilot Licence (Aeroplane), but at the time of the incident was exercising the privileges of a Private Pilot Licence, with an instrument rating and a valid Class 2 Aviation Medical Certificate. The pilot had a total flying experience of about 16,800 hours, they had accrued about 9,800 hours on the Aero Commander 500-S and about 4,700 hours total instrument time. The pilot completed their instrument proficiency check on 29 June 2021 and last flew an RNAV approach in instrument meteorological conditions (IMC) on 6 August 2021.

Weather observations

The pilot reported being aware of forecast IMC prior to departing Port Lincoln and planned their flight accordingly. They reported operating in cloud until the aircraft had descended to 1,000 ft on approach for runway 05, and turbulence from 6,000 to 3,000 ft, with the intensity increasing between 4,000 ft and 3,000 ft.

The pilot’s observations were consistent with the forecast weather conditions.

Garmin GTN 650 touchscreen

The Garmin GTN 650 is a navigation aid that combines GPS, communication and navigation functions in an MFD, capable of showing high resolution terrain mapping, graphical flight planning, multiple weather options and traffic display. The touchscreen uses capacitive technology to sense the proximity of skin to the display, responding to light touches, without the need of pressure for detection.

Functions related to this incident include a ‘Direct-To’ key, which when pressed provided a direct course to a selected waypoint. The navigation and communication frequencies could be changed by touching the standby window and the keypad to enter the desired frequency. To flip between active and standby frequencies, the operator needed to touch the active navigation/communication frequency field (Figure 3). Upon touching the frequency field, a text box ‘Hold for Flip-Flop’ is displayed near the knob. If the active navigation/communication frequency field is touched and held it will switch between the navigation and communication frequencies.

Figure 3: Garmin GTN 650 display screen

Source: Garmin, annotated by the ATSB

The pilot reported that when operating in turbulent conditions, they usually put two fingers on the side of the display to stabilise their hand and use their thumb to enter the data. After missing the initial approach fix, and during the second attempt to enter the waypoint into the MFD, the pilot reported that their finger slipped and inadvertently selected the Melbourne Centre frequency, which was the previous frequency selected.

Workload

Speed and timeframe

During the descent, the aircraft’s airspeed was about 170 kt. The pilot reported receiving a late descent to commence the RNAV-Z approach, which resulted in the aircraft being too high and fast to commence the approach. The pilot reported feeling rushed due to the combination of speed and the timing of the descent and approach clearances. The pilot reported their ideal approach speed would be 120-140 kt. However, data from previous flights inbound to Adelaide, that were probably flown by the pilot, show the aircraft conducting approaches at similar speeds.  

Handling speeds for instrument approaches are specified in Airservices Australia’s Aeronautical Information Publication, En Route 1.16.1 These included a range of 120–180 kt indicated airspeed for Category B aircraft during the initial and intermediate approach. VH-LTP was within this range when the pilot was cleared to conduct the RNAV approach.

Monitoring

When assigned heading 120°, the pilot realised the aircraft had climbed since the turning onto the 360° heading, and therefore commenced a descent to the assigned altitude. However, the pilot was unaware the aircraft had subsequently continued to descend while they were out of communication with Adelaide Approach.

The pilot recalled becoming aware that something was wrong when they had not received any further instructions from ATC and recognised the voice of the Melbourne Centre controller. This prompted the pilot to contact the controller, who transferred them back to Adelaide Approach.

Self-assessment

The pilot rated their workload during the incident as 7 out of 10. The pilot reported that typically during an approach, their workload is ‘not too bad’, however, in this incident, the turbulence, difficulties entering in the waypoint, the late clearance for descent and then the aircraft turning away from the approach added to their workload. The pilot thought they were coping well with the situation, but advised that they were busy, with the situation moving quickly and little things were adding up.

Safety analysis

Data entry difficulties

The pilot’s data entry difficulties were consistent with the research conducted on touchscreen interfaces. During turbulent conditions, aircraft touchscreen interfaces have been known to increase data input errors and create slow interaction times. This is due to the display moving or vibrating independently of the pilot's body, which is itself also vibrating. A study conducted by Dodd and others (2014) found that while operating in moderate turbulence, it took pilots over 2 minutes longer to complete a given task when compared to operating in no turbulence. Although necessary when operating in turbulent conditions, stabilising the hand on the edge of the screen can also increase the risk of accidental presses on the edge of the screen (Coutts and others. 2019).

Ineffective monitoring

The pilot was experiencing a high workload, likely due to operating in instrument meteorological conditions, turbulence, encountering data entry difficulties and feeling rushed. This high workload likely resulted in the pilot not initially noticing the frequency change nor the continued descent and descent below the assigned altitude, which was the minimum sector altitude.

Workload is defined as the sum of task demands placed on an individual’s cognitive resources that are used for attention, perception, decision making and action (Skybrary, 2010). Humans are limited in the amount of new information their brain can process at once. Once this limit of cognitive resources has been reached their performance starts to decline with increased error rates and delayed responses, thus resulting in cognitive overload.

During high workload periods, monitoring flight instruments can degrade due to other tasks requiring attention, which can potentially lead to undetected errors (Flight Safety Foundation, 2014). A study on controlled flight into terrain (CFIT) conducted by the International Civil Aviation Organization, Flight Safety Foundation and the United States Federal Aviation Administration (Flight Safety Foundation, n.d.), found that two thirds of all CFIT accidents are a result of altitude error or lack of vertical situational awareness.

Though the pilot reported that they were coping well, pilots are often unaware that their monitoring performance has degraded, subsequently affecting their situational awareness.

Findings

From the evidence available, the following findings are made with respect to the descent below the minimum sector altitude involving an Aero Commander 500-S, registered VH-LTP that occurred near Adelaide Airport, South Australia, on 12 August 2021.

Contributing factors

• Due to turbulence, the pilot had difficulties entering data into the touchscreen multi-function display and the pilot inadvertently selected the incorrect radio frequency.
• The pilot was likely experiencing high workload in instrument meteorological conditions resulting in a loss of situational awareness and ineffective monitoring of the instruments. This led to the aircraft descending below the minimum sector altitude before the pilot regained communication with air traffic control.

Other findings

• The air traffic controller issued another terrain safety alert to the pilot after communications were restored, which likely prevented a controlled flight into terrain accident.

Sources and submissions

Sources of information

The sources of information during the investigation included:

• the pilot
• Airservices Australia
• Bureau of Meteorology
• Geoscience Australia.

References

• Coutts, L.V., Plant, K.L., Smith, M., Bolton, L., Parnell, K.J., Arnold, J., & Stanton, N.A. (2019). Future technology on the flight deck: assessing the use of touchscreens in vibration environments. Ergonomics, 62(2), 286-304. https://doi.org/10.1080/00140139.2018.1552013
• Dodd, S., Lancaster, J., Miranda, A., Grothe, S., DeMers, B., & Rogers, B. (2014). Touch Screens on the Flight Deck: The Impact of Touch Target Size, Spacing, Touch Technology and Turbulence on Pilot Performance. Proceedings of the Human Factors and Ergonomics Society 58^th Annual Meeting, 58(1), 6-10. https://doi.org/10.1177/1541931214581002
• Flight Safety Foundation (n.d.). Controlled Flight into Terrain: Education and Training Aid. Flight Safety Foundation. https://skybrary.aero/sites/default/files/bookshelf/2507.pdf
• Flight Safety Foundation (2014). A Practical Guide for Improving Flight Path Monitoring: Final report of the active pilot monitoring group. Flight Safety Foundation. https://flightsafety.org/files/flightpath/EPMG.pdf
• Skybrary (2010). Workload (OGHFA BN). Skybrary. https://www.skybrary.aero/index.php/Workload_(OGHFA_BN)

Submissions

Under section 26 of the Transport Safety Investigation Act 2003, the ATSB may provide a draft report, on a confidential basis, to any person whom the ATSB considers appropriate. That section allows a person receiving a draft report to make submissions to the ATSB about the draft report.

A draft of this report was provided to the following directly involved parties:

• the pilot
• the aircraft operator
• Airservices Australia.

A submission was received from the pilot. The submission was reviewed and, where considered appropriate, the text of the report was amended accordingly.

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through: identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. Terminology An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing information Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 2022 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence. Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work. The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

__________

1.  Central Standard Time (CST): Coordinated Universal Time (UTC) + 9.5 hours.
2.  Instrument flight rules (IFR): a set of regulations that permit the pilot to operate an aircraft in instrument meteorological conditions (IMC), which have much lower weather minimums than visual flight rules (VFR).
3.  Area navigation (RNAV) approach: An approach flown along a path of GPS waypoints.
4.  Instrument meteorological conditions (IMC): weather conditions that require pilots to fly primarily by reference to instruments, and therefore under instrument flight rules (IFR), rather than by outside visual reference. Typically, this means flying in cloud or limited visibility.
5.  Melbourne Centre: Responsible for enroute services throughout the Melbourne flight information region, which includes the southern half of Australia and the Southern and Indian oceans.

Safety summary

What happened

On the evening of 13 May 2021, a Hartwig Air Beechcraft Baron 95-B55 aircraft, registered VH‑CBG, departed Ceduna Airport, South Australia (SA), for a charter flight under the instrument flight rules (IFR) to Parafield Airport, SA, with the pilot and one passenger on‑board. During the flight, the autopilot system did not function as the pilot expected.

At 1851, the aircraft was cleared for a night visual approach and descended towards Parafield Airport. At the time, the pilot’s focus was on the autopilot, resulting in the pilot losing sight of the runway and inadvertently overflying the airport towards an area of rising terrain at an altitude well below the minimum safe altitude. The pilot maintained this altitude and continued the approach while looking for the runway. Despite the night conditions, there was enough light for the airport tower controller to see the aircraft and the hill‑line to the east, so its terrain clearance did not raise concerns.

At 1855, the aircraft re-entered the Parafield control area and was cleared for a visual approach to the runway, landing shortly thereafter.

What the ATSB found

The ATSB found that during the night visual approach under the IFR, the pilot lost situational awareness, probably as a result of distraction due to a perceived autopilot system issue. The approach was then continued at an altitude below the minimum safe altitude, removing obstacle clearance assurance.

What has been done as a result

The operator’s pilot training program has been updated to include a threat and error management course.

Airservices Australia advised that Parafield Airport tower controllers will be provided with a briefing paper about the incident and incorporate any learning opportunities and safety messaging from the ATSB investigation. The briefing will include information on the circling area, descent below the minimum safe altitude during visual approaches, go-arounds, and the ‘safety alert’ procedure. This procedure is intended to warn pilots that their aircraft is in unsafe proximity to terrain, obstruction, active restricted/prohibited areas, or other aircraft.

Safety message

Handling of approaches is one of the ATSB’s SafetyWatch priorities. Due to the reduced visibility at night, a night approach requires even greater pilot awareness. Unless there is a problem affecting flight safety, pilots should remain focussed on monitoring aircraft and approach parameters, which provides assurance that an approach can be safely completed. If a visual approach cannot be completed, pilots must inform air traffic control so assistance can be provided.

If the criteria for the safe continuation of an approach are not met, for example losing sight of the runway, pilots must initiate a go-around and attain a safe altitude to reduce the risk of colliding with obstacles or terrain.

The investigation

The occurrence

On 13 May 2021, at 1700 Central Standard Time, ^[1] a Hartwig Air Beechcraft Baron 95-B55 aircraft, registered VH-CBG (Figure 1), departed Ceduna Airport, South Australia (SA), for a charter flight under the instrument flight rules (IFR) ^[2] to Parafield Airport, SA, with the pilot and one passenger on-board.

Figure 1: VH-CBG

Source: Andrew Lesty

During the flight, the pilot noted that when the autopilot was engaged, the aircraft was ‘snaking left to right’ but felt that, overall, its tracking was not greatly affected (the aircraft’s slight left and right lateral motion during the flight was evident in the aircraft’s tracking data). The pilot had also observed the same behaviour on an earlier flight that day.

At 1841, the aircraft was located about 22 NM from the waypoint ^[3]PORTA (Figure 2). At that time, Adelaide Approach air traffic control (ATC) instructed the pilot to turn left, and 4 minutes later, turn 

right to separate the aircraft from other traffic. The pilot switched the autopilot from navigation (NAV) to heading (HDG) ^[4] mode and complied with the instructions.

At 1847, the pilot was instructed to resume navigation to PORTA. The pilot recalled switching the autopilot back to NAV mode to track toward PORTA, but the aircraft continued along the previously assigned heading, about 20° to the left of the track to PORTA. Shortly after, ATC requested the pilot to confirm tracking, and after the pilot acknowledged, the aircraft gradually turned right over the next minute until 1849, when it tracked toward PORTA.

Figure 2: Aircraft track from 1838 to 1901

Source: Google Earth, annotated by ATSB

At 1850, the aircraft was travelling south-east, descending over PORTA at a ground speed of 165 kt (the forecast wind was 20 kt from the south-west) and the autopilot initiated a turn towards the Parafield Airport non-directional beacon (NDB). The aircraft did not turn as quickly as the pilot anticipated, so the autopilot was disconnected, and the pilot completed the turn manually before re-engaging the autopilot.

One minute later, the pilot contacted the Parafield Airport Tower controller and was instructed to descend to 1,500 ft once established in the circling area for runway 21R (see the section titled Circling area), and report ‘visual’ ^[5] (it was dark at the time). At the same time, two other aircraft were conducting circuits ^[6] on runway 21R. The pilot selected the autopilot NAV mode to track to the Parafield NDB and reported ‘visual’.

Eighty seconds later, the aircraft descended below 1,700 ft above mean sea level (AMSL) at a ground speed of 180 kt with a 20 kt tailwind. The controller then instructed the pilot to join the right downwind leg of the circuit for the runway. After the pilot acknowledged the instruction, the aircraft continued toward the airport before commencing a slight left turn onto a heading of 022° magnetic, consistent with a downwind heading, but almost directly overhead the runway (Figure 3).

The aircraft passed over the control tower, in line with the upwind leg of the circuit for the reciprocal runway (03L) and descended to about 1,330 ft. At the same time, another aircraft was at 700 ft and turning onto the final leg of the circuit for runway 21R, so the tower controller instructed the pilot of CBG to maintain 1,500 ft. At this time, the pilot believed (incorrectly) that the aircraft was positioned on the downwind leg for runway 21R. Seventeen seconds later, the controller instructed the pilot to make a right turn with the intention of repositioning the aircraft to join final for runway 21R via a teardrop turn.

At 1854, the pilot started a right turn, during which the aircraft proceeded outside both the circling area and Parafield control area (see the section titled Airspace) at an altitude of 1,400 ft and a groundspeed of 157 kt. During the right turn, the pilot could not see the runway and continued flying south-east at 1,400 ft while looking for it.

About 30 seconds later, the tower controller requested confirmation that the pilot was returning to the airport and informed them that the aircraft was in non‑controlled airspace (see the section titled Airspace). Although it was dark, there was enough light for the controller to see the aircraft and the hill-line to the east, and therefore, they were not concerned about the aircraft’s terrain clearance. The pilot maintained a stable aircraft attitude and altitude as they could see the artificial street lighting on the ground, had good visibility ahead and below the aircraft, and were generally familiar with Parafield Airport.

After the pilot confirmed the intention to return to Parafield, the aircraft continued tracking away from the airport and the controller then instructed the pilot to track direct to the airport, maintain 1,500 ft, and join the upwind leg of the circuit. At 1855, with the aircraft still travelling south away from the airport, the controller requested confirmation that the pilot could see the airport. The pilot acknowledged and turned the aircraft towards Parafield Airport.

Figure 3: The approach

Source: Google Earth, annotated by ATSB

At 1856, the tower controller cleared the aircraft for a visual approach. The aircraft joined the circuit via the crosswind circuit leg for runway 21R, with a subsequent downwind leg ground speed of 138 kt and altitude of 1,000 ft, before landing safely at 1901.

Context

Pilot

The pilot held a Commercial Pilot Licence (Aeroplane) with a total flying time of 1,185 hours, having flown 82 hours in the previous 90 days. The pilot’s total time included 227 hours on the Beechcraft Baron 95-B55 aircraft and a total night flying time of 20 hours.

In discussing the incident, the pilot stated:

• The behaviour of the autopilot led them to lose confidence in its performance and partly focus on the autopilot during the approach (no defect with the autopilot system was identified after the flight).
• They felt they were ‘slipping behind the aircraft’ while inbound to Parafield from PORTA.
• When the aircraft flew over the control tower in line with the runway, they believed the aircraft was positioned on the downwind leg.
• They were not aware that the aircraft left the circling area and the control area.
• There was no interaction with the passenger seated in the rear of the aircraft during the approach.

The ATSB collected information about the pilot’s 72 hours of activity prior to the incident, including a statement from the pilot that they felt ‘a little tired’ during the approach to Parafield. However, a review of the evidence identified that it was unlikely that the pilot was experiencing a level of fatigue known to affect performance.

Airspace

Parafield Airport is situated within Class D terminal airspace extending from the ground level up to an altitude of 1,500 ft. This airspace was controlled by an air traffic controller situated in the Parafield control tower. The airspace bordered both the Royal Australian Air Force Base Edinburgh airspace to the north and Adelaide Airport airspace to the south (Figure 4). The airspace east of Parafield Airport was non‑controlled up to 2,500 ft, with Adelaide Airport Class C airspace above that altitude.

Figure 4: Parafield control area

Source: Airservices, annotated by ATSB

Night visual approach criteria

Minimum altitude requirements during the conduct of a visual approach at night under the IFR is provided in section 1.1 of the Aeronautical Information Publication (AIP) En Route:

En Route 1.1:

- Paragraph 2.11.3.7 Minimum Altitude Requirements

During the conduct of a visual approach, a pilot must descend as necessary to:

…b. by night:

(1) For an IFR flight:

…Maintain an altitude not less than the route segment…MSA [minimum sector altitude]…until the aircraft is:

…within the prescribed circling area for the category of aircraft…and the aerodrome is in sight.

- Paragraph 2.11.3.9

…A pilot who is unable to continue a visual approach which has been authorised by ATC must immediately advise ATC.

Within a 10 NM radius of Parafield Airport, the minimum sector altitude (MSA) was 3,800 ft AMSL, which provided a minimum terrain clearance of 1,000 ft above all objects.

Circling area

The circling area is an area bounded by arcs drawn from the runway thresholds, with the radius of the arcs dependent on an aircraft’s performance category (Category A to E). The performance categories are based on an aircraft’s approach speed range. The Beechcraft Baron 95-B55 was a Category B aircraft with a circling area of 2.66 NM.

The Category B circling area provides obstacle clearance of not less than 300 ft at an altitude not below the appropriate minimum altitude for circling, which in this case was 1,580 ft. Circling was prohibited to the east of runway 21R at Parafield Airport due to relatively high terrain (Figure 5).

Figure 5: Circling area

Source: Google Earth, annotated by ATSB

Safety analysis

The aircraft’s track and its handling during the night approach was abnormal. This included a high inbound airspeed and incorrect downwind positioning. The pilot’s statements and recorded aircraft tracking indicate a loss of situational awareness, which involves three stages:

• obtaining information
• understanding of what is going on around you
• identifying what is likely to happen next.

The loss of situational awareness was probably due to the perceived issue with the aircraft’s autopilot system, which distracted the pilot from managing the approach.

As the approach progressed, the pilot’s situational awareness became increasingly compromised, resulting in the aircraft being manoeuvred beyond both the circling area and the Parafield control area at an altitude significantly below the minimum sector altitude.

After turning onto what the pilot incorrectly believed was the circuit’s base leg, the runway could not be visually identified, but the approach was continued while looking for the runway. Familiarity with the airport and a favourable assessment of the prevailing visibility conditions led the pilot to believe that the safest option was to remain within the proximity of the airport and maintain the aircraft’s altitude.

However, the pilot had lost sight of the airport at night when the ability to visually identify obstacles was limited, so the safest option was to climb to the minimum safe altitude. Continuation of the night visual approach well below the minimum safe altitude removed obstacle clearance assurance and increased the terrain collision risk.

Findings

From the evidence available, the following finding is made with respect to the flight below minimum safe altitude involving Beechcraft Baron 95-B55, VH-CBG 5 km north of Parafield Airport, South Australia on 13 May 2021.

Contributing factor

• During the night visual approach under the instrument flight rules the pilot lost situational awareness, probably as a result of distraction due to a perceived autopilot system issue. The approach was then continued at an altitude below the minimum safe altitude, removing obstacle clearance assurance.

Safety actions

Safety action by Hartwig Air

The operator advised the ATSB that the operator’s pilot training program was being updated to include a threat and error management course.

Safety action by Airservices Australia

Airservices Australia advised the ATSB that Parafield Airport tower controllers will be provided with a briefing paper about the incident and incorporate any learning opportunities and safety messaging from the ATSB investigation. The briefing will include information on the circling area, descent below the minimum safe altitude during visual approaches, go-arounds, and the ‘safety alert’ procedure.

This procedure states that unless a pilot has advised that action is being taken to resolve an unsafe situation, a tower controller can communicate a safety alert to an aircraft when the controller becomes aware that it is in a situation that places it in unsafe proximity to:

• terrain
• obstruction
• active restricted or prohibited areas
• other aircraft.

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• operator
• pilot
• Airservices Australia
• Bureau of Meteorology

Submissions

Under section 26 of the Transport Safety Investigation Act 2003, the ATSB may provide a draft report, on a confidential basis, to any person whom the ATSB considers appropriate. That section allows a person receiving a draft report to make submissions to the ATSB about the draft report.

A draft of this report was provided to the following directly involved parties:

• operator
• pilot
• controller
• Airservices Australia
• Civil Aviation Safety Authority.

The controller provided a submission, which was reviewed and, where considered appropriate, the text of the report was amended accordingly.

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through: identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. Terminology An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing information  Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 2021 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence. Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work. The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

__________

1.  Central Standard Time (CST): Coordinate Universal Time (UTC) + 9.5 hours.
2.  Instrument flight rules (IFR): a set of regulations that permit the pilot to operate an aircraft in instrument meteorological conditions (IMC), which have much lower weather minimums than visual flight rules (VFR). Procedures and training are significantly more complex as a pilot must demonstrate competency in IMC conditions while controlling the aircraft solely by reference to instruments. IFR-capable aircraft have greater equipment and maintenance requirements.
3.  Waypoint: A defined position of latitude and longitude coordinates, primarily used for navigation.
4.  In NAV mode, the autopilot system follows the lateral path commanded by the GPS. When HDG mode is selected, the autopilot steers the aircraft according to a heading manually selected by the pilot.
5.  A request to the pilot to confirm the criteria for visual conditions are met so a visual approach clearance could be authorised by air traffic control (see section 1.1 of the Aeronautical Information Publication (AIP) En Route).
6.  Circuit: a specified pattern flown by aircraft when taking off or landing while maintaining visual contact with the airfield. Typically rectangular in shape and include pattern legs; upwind, crosswind, downwind, base and final.

Safety summary

What happened

In the early afternoon of 22 March 2021, a Piper PA‑31P‑350 Mojave aircraft, registered VH-XGW, departed Dubbo Airport, New South Wales (NSW), for a flight conducted under the instrument flight rules to Bankstown Airport, NSW, with one pilot and a crew member on board.

On arrival at Bankstown, the pilot commenced a GPS instrument approach for runway 11C. While the initial part of the approach proceeded normally, the aircraft was observed by the Bankstown tower controller to track 0.5 NM (0.9 km) to the south of the required track, and this was advised to the pilot. After the aircraft passed the final approach fix, due to continued deviation, the tower controller instructed the pilot to discontinue the approach.

The pilot initially acknowledged that instruction but then requested, and was approved by the controller, to continue the approach visually as the aircraft had descended clear of cloud. The pilot then conducted extensive manoeuvring, including two orbits, at low altitude that were not in accordance with the approach requirements, before landing the aircraft safely on runway 11C.

What the ATSB found

The ATSB identified that, while conducting an instrument approach into Bankstown Airport in instrument meteorological conditions, the pilot did not conduct a missed approach when the aircraft exceeded the tracking tolerance limits. That resulted in the aircraft operating significantly below the minimum allowable altitude.

Additionally, having descended visually below the minimum descent altitude and commenced manoeuvring to position the aircraft for a landing at Bankstown Airport, the pilot did not conduct a missed approach when the aircraft exited the circling area and the required visual reference with the runway was lost.

Safety message

Managing approaches is one of the ATSB’s SafetyWatch priorities. Adherence to operational procedures ensures consistency of pilot action and aircraft operation during the approach and landing phases of flight. This, along with careful monitoring of aircraft and approach parameters, ensures instrument approaches are conducted safely.

Most importantly, if the criteria for safe continuation of an approach are not met, the pilot should conduct a missed approach to negate the risk of colliding with obstacles or terrain.

The investigation

The occurrence

On 22 March 2021 the pilot of a Piper PA-31P-350/A1 Mojave, registered VH-XGW (Figure 1) conducted pre-flight preparations for an early afternoon flight from Dubbo, New South Wales (NSW), to Bankstown, NSW. The flight was to preposition the aircraft at Bankstown for a medical transport flight planned for later that day. The crew for the flight from Dubbo comprised the pilot and a flight nurse. The aircraft was fitted with a Global Positioning System (GPS)^[1] navigation unit and autopilot.

Figure 1: VH-XGW

A photo of VH-XGW.

Source: JETPHOTOS, Kynan Schneider

The aerodrome forecast for Bankstown,^[2] which was obtained by the pilot and covered the period from 1100 Eastern Daylight‑saving Time^[3] through to 2200, stated that the expected visibility was greater than 10 km with light rain showers and scattered^[4] cloud at 1,500 ft above mean sea level (AMSL) and broken cloud at 2,500 ft.

The forecast included temporary changes, where visibility would reduce to 3,000 m in moderate rain showers and the cloud cover would include a broken layer at 800 ft. Having reviewed the forecast and other planning data, the pilot submitted a flight plan, which stated that the flight’s planned duration was 58 minutes, the aircraft had an endurance in excess of 4 hours, and that the flight would be conducted under instrument flight rules (IFR).^[5] The flight plan also stated that the aircraft was performance category B (CAT B) (see the section titled Circling area).

At 1343, the aircraft departed Dubbo for Bankstown. As the aircraft approached Bankstown, the pilot was cleared to conduct an RNAV-Z_(GNSS)RWY11C (RNAV-Z) instrument approach procedure into Bankstown (see the section titled Bankstown RNAV-Z approach). At 1448, the pilot called Bankstown tower and reported approaching the RNAV-Z intermediate approach fix at an altitude of 2,500 ft. In response, the tower instructed the pilot to report at the final approach fix (SBKWF). At this point in the flight the aircraft was in cloud. The pilot reported that the approach into Bankstown was predominantly flown with the use of the aircraft’s autopilot.

Figure 2 shows the aircraft’s flight path^[6] in relation to the RNAV-Z instrument approach procedure’s required track. The aircraft passed abeam the intermediate approach fix (SBKWI) at 1449:30 and then began diverging from the RNAV-Z approach path as it tracked towards the final approach fix (SBKWF). Approaching SBKWF, the tower advised the pilot that the aircraft was tracking 0.5 NM (0.9 km) to the south of the approach path and enquired whether aircraft operations were normal. The pilot responded that operations were normal.

After the aircraft passed abeam SBKWF, the tower instructed the pilot to conduct the missed approach due to the continued significant deviation from the expected flight path. The pilot responded, ‘going around’–at that time the aircraft was descending through 1,100 ft. Despite the pilot advising the intention to commence the missed approach, further communications then ensued, during which the pilot requested to conduct a circling approach. In response the tower enquired about whether the pilot was visual, and the pilot advised that they were. The aircraft continued to descend and track towards the runway. About 30 seconds after the pilot called ‘going around’, the tower acknowledged the pilot’s ‘visual’ declaration and instructed the pilot to join final for runway 11C.

Figure 2: Aircraft flight path in relation to the RNAV-Z track and related key events

A Google Earth image of the aircraft’s approach track with significant events and locations marked.

Source: Google Earth and Airservices Australia, modified by the ATSB.

The pilot advised that, on receipt of the amended tracking instruction from the tower, they checked the GPS distance readout and confirmed that the aircraft was established within the CAT B circling area. Shortly after, the pilot stated that the aircraft entered a rain shower and visibility was momentarily reduced. To retain visual flight conditions, the pilot initiated a sharp left turn. Also, at about this time, the tower cleared the aircraft to land, which the pilot read back.

At 1452:28, as the aircraft was observed to be tracking away from the runway and at an altitude of 500 ft, the tower issued a safety alert for terrain to the pilot, which the pilot acknowledged. The tower followed this up with confirmation that the QNH^[7] was 1019 (hPa), which the pilot read back. The aircraft continued the left turn to complete a full left orbit. During this orbit, the aircraft descended to an altitude of 400 ft as it crossed the RNAV-Z approach path the second time tracking south. The terrain elevation in that area is about 100 ft.

At 1453:05, as the aircraft exited the orbit to the west of the Warwick Farm racecourse at an altitude of 500 ft, the tower issued a second safety alert for terrain as they had lost sight of the aircraft. The pilot responded that the aircraft was over the Georges River (adjacent to Warwick Farm racecourse) and manoeuvring. Shortly after, the tower advised the pilot that they had regained sight of the aircraft.

The pilot then commenced a second left orbit at an altitude of between 5-600 ft. During this second orbit the tower requested confirmation that the pilot had the aerodrome in sight. The pilot responded in the affirmative, and that the intention was to ‘sort some things out’ while over the racecourse. The tower then instructed the pilot to join final, track as required and report established on final. The pilot acknowledged the instruction. The aircraft had, by then, completed the second orbit and commenced tracking towards the aerodrome. Shortly thereafter, the tower provided further advice concerning weather to the north of the airfield. In response, the pilot positioned the aircraft for a right circuit to runway 11C and landed at 1458.

The pilot later reported that the aircraft performed normally during the flight and that there were no faults with the aircraft or it’s navigation systems.

Context

Instrument approach requirements

Aeronautical Information Publication (AIP) ENR 1.1 paragraph 2.11.2.1^[8] provided that, unless authorised to make a visual approach, an IFR flight must conform to the published instrument approach procedure nominated by air traffic control (ATC). A pilot can request ATC authorisation to deviate from an instrument approach procedure, and that subsequent authorisation is deemed an instruction from ATC.

The Bankstown automatic terminal information service (ATIS)^[9] information valid at the time of the occurrence identified that an instrument approach procedure was required for the approach and landing into Bankstown. The relevant components of the information were that:

• runway 11C was in use
• instrument approach procedures were in place
• visibility was 8,000 m, reducing to 3,000 m in rain showers
• cloud comprised few at 1,000 ft, scattered at 2,000 ft and broken at 3,000 ft
• the QNH was 1019 hPa.

Bankstown RNAV-Z approach

The RNAV-Z_(GNSS)RWY11C approach procedure (Figure 3) is a non-precision approach (NPA) that uses GNSS signals for a 2-dimensional instrument approach procedure. The following features from the chart are relevant to the approach:

• The approach is designed as a straight-in approach to runway 11C, with the option of conducting circling approaches to the airport’s runways.
• The minima titles are shaded. This identifies that the published minima could be reduced by 100 ft when using an actual QNH, such as that provided by the Bankstown ATIS.
• The approach minima, based on the aircraft’s performance category CAT B^[10] as reported in the flight plan, were:
  • for the straight-in approach, the minimum descent altitude (MDA) of 580 ft AMSL
  • for the circling approach, the MDA of 650 ft AMSL.
• The plan profile of the chart identified several obstacles around the approach and missed approach track. The highlighted obstacles had the potential to directly affect the approach and/or missed approach flight paths when below the approach minima.^[11]
• The minimum safe altitude within 15 NM of Bankstown Airport was 2,500 ft AMSL.

Figure 3: The RNAV-Z_(GNSS)RWY 11C approach procedure chart

Source: Airservices

The circling area

The required obstacle clearance for circling approaches is established by applying a radius distance, which is based on the aircraft’s performance category, to the threshold of all runways usable by that category of aircraft. For a CAT B aircraft, that radius is 2.66 NM. Tangents are then drawn from the extremities of the arcs to complete the circling area (Figure 4). The circling minima is then determined by applying the required obstacle clearance value of 90 m, or approximately 300 ft, to the highest obstacle within that area.

The pilot reported that, during the conduct of the instrument approach and the subsequent visual manoeuvring, an available option was to remain inside the higher CAT C circling limits (based on a radius of 4.2 NM) and above the required obstacle clearance limit of 400 ft.

The pilot also stated that at no time was the aircraft’s barometric altimeter observed to go below 400 ft. However, with an accurate QNH set, that instrument measures height AMSL within defined accuracy tolerances. Consequently, operating at an altitude of 400 ft within the CAT C circling area for Bankstown Airport did not provide the required terrain clearance as it did not allow for the terrain elevation and obstacles.

Figure 4: CAT B circling area construction

Source: ICAO Doc 8168 Volume II.

Approach tolerances for the RNAV-Z approach

The following lateral approach tolerances applied to the RNAV-Z approach into Bankstown Airport:^[12]

• For the intermediate segment of the approach, the required navigation performance (RNP)^[13] is 1.0 NM, which is displayed as full-scale deflection on a course deviation indicator (CDI)^[14] to the pilot. The target level of safety performance for this segment is within half‑scale CDI deflection—that is 0.5 NM.
• From 2 NM before the final approach fix, the GPS tracking display transitions to the final segment RNP of 0.3 NM, displayed as full‑scale CDI deflection. The target level of safety performance for the final segment is also half-scale CDI deflection—that is 0.15 NM.
• Under Civil Aviation Order 20.91,^[15] a missed approach must be executed if, during the segment of a procedure, the cross-track error/deviation equals or is reasonably likely to equal, the RNP for segment of the procedure.

The aircraft’s GPS unit automatically sets the aircraft navigation instruments’ CDI scale to the RNP limits for the various segments of the RNAV-Z procedure as described above.

An aircraft must be ‘established’ on the instrument approach procedure’s track before commencing descent on the approach procedure.^[16] Established was defined as within half-scale deflection for GNSS type approaches.

Application of the approach tolerances to the occurrence flight path

The aircraft’s flight path with respect to the approach tolerances is displayed in Figure 5. The half‑scale and full-scale limits are displayed as a surface set to the segment’s minimum segment altitude of 1,400 ft. while the full-scale tracking limits are displayed as the outer red line. The transition from the intermediate segment’s RNP 1.0 NM to the final segment’s RNP 0.3 NM is displayed as a progressively decreasing maximum permissible displacement (decreasing tolerance) from 2.0 NM before final approach fix (SBKWF).

The aircraft’s track early in the intermediate approach segment was within tolerances, but progressively diverged from the required approach path. The decreasing tolerance from 2 NM before SBKWF and the divergent flight path resulted in the aircraft rapidly exceeding the required tracking tolerances for the intermediate segment. It was at around this point in the approach that the tower alerted the pilot to the aircraft tracking 0.5 NM south of the required instrument approach path. As the aircraft passed abeam SBKWF, it was significantly outside of the full-scale RNP limit at an altitude of 1,400 ft.

Figure 5: The aircraft’s initial approach flight path in relation to tracking tolerances

Source: Google earth and Airservices, modified by ATSB.

The aircraft’s flight path with respect to the approach tolerances in the final approach segment is displayed in Figure 6. After passing abeam the final approach fix the aircraft’s lateral displacement from the required approach track exceeded the full‑scale RNP limit.

During the final approach segment, the aircraft’s track converged with the required track, but the aircraft was not established within the required tracking tolerances until after the pilot reported being visual to ATC.

At the commencement of the left orbit, and as the aircraft crossed the approach track for the first time, the aircraft was above the straight‑in approach minimum descent altitude of 580 ft. As the orbit continued and the aircraft crossed the approach track for the second time, the aircraft was below the 930 ft segment minimum altitude and had descended below the 580 ft approach minimum descent altitude. The aircraft was also outside of the CAT B circling area (represented by the light blue arc).

Figure 6: The aircraft’s final approach flight path in relation to tracking tolerances

Source: Google earth and Airservices, modified by ATSB

Missed approach requirements

AIP ENR 1.5 paragraph 1.10.1^[17] contained specific circumstances where a missed approach must be conducted. These included:

• during the final segment of an instrument approach, where the aircraft is not maintained within the applicable navigation tolerance for the aid in use
• when the required visual reference is not established at or before reaching the missed approach point from which the missed approach procedure commences
• when a landing cannot be made from a runway approach, unless a circling approach can be conducted in weather conditions equal to or better than those specified for circling
• when visual reference is lost while circling to land from an instrument approach.

In a note following these requirements, ‘visual reference’ was defined as meaning the runway threshold, or approach lights or other markings identifiable with the landing runway were clearly visible to the pilot, and for circling approaches, clear of cloud, in sight of the ground or water and with a flight visibility not less than the minimum specified for circling.

Descent from the minimum descent altitude to the runway

The aim of an instrument approach procedure is to position the aircraft so that the pilot can establish visual contact with the runway and land. The AIP detailed the requirements for the transition from the instrument approach procedure and descent from the MDA to positioning for a landing. These requirements varied depending on whether a straight-in approach or a circling approach was being conducted.

Straight-in approach

For a straight-in approach, AIP ENR 1.5 paragraph 1.8.2^[18] stated that, provided the required meteorological minima are met, descent below the straight-in MDA may only occur when:

• visual reference can be maintained and
• the aircraft is continuously in a position from which a descent to a landing on the intended runway can be made at a normal rate of descent using normal flight manoeuvres that will allow touchdown to occur within the touchdown zone of the runway of intended landing.

The definition of ‘visual reference’ in this context is the same as previously detailed in the section titled Requirements for a missed approach.

Circling approach

The circling approach and visual circling rules are more complex than those for the straight-in approach. The following components of these rules are relevant:^[19]

During visual circling, descent below the circling MDA may only occur when the pilot

a. maintains the aircraft within the circling area; and

b. maintains a visibility, along the intended flight path, not less than the minimum specified on the chart for the procedure; and

c. maintains visual contact with the landing runway environment (i.e. the runway threshold or approach lighting or other markings identifiable with the runway); and either ...

e. in daylight only, while complying with a., b. and c., maintains visual contact with obstacles along the intended flight path and an obstacle clearance not less than the minimum for the aircraft performance category until the aircraft is aligned with the landing runway.

Notes that followed these rules stated the following:

Note 1: The concept is as follows: ...

(2) When daylight exists and obstacles can be seen, the pilot has the option of descending from MDA from any position within the circling area while maintaining an obstacle clearance not less than that required for the aircraft performance category.

(3) Once the pilot initiates descent below circling MDA, the obstacle protection offered by visual circling at the MDA ends and they are responsible for ensuring the required clearance from obstacles is maintained visually.

Guidance on non-precision approaches

The Civil Aviation Advisory Publication (CAAP) 178-1(2)^[20], provided guidance on the conduct of an NPA, such as the Bankstown Airport RNAV‑Z approach. The CAAP compiled all relevant regulation, standards, and practices into a single document, but also recommended that it be read in conjunction with those sources.

Straight-in approach

The CAAP stated that it is commonly acknowledged that straight-in approaches are significantly safer than circling approaches. For an NPA with a straight in approach, once the criteria for descent from the MDA are met, the required approach path from the MDA to the runway is protected from obstacles by aerodrome and instrument procedure design standards. The visibility requirement for the straight-in approach is based on the distance from the runway threshold where a normal 3-degree approach descent path to the runway intercepts the MDA.

Circling approach

Circling approaches normally require manoeuvring to align the aircraft with a suitable runway other than the designated straight‑in runway. Circling is a visual procedure that can be hazardous if not executed correctly. Visibility for circling operations is based on the relevant aircraft category’s radius of turn, in adverse wind conditions, to enable the aircraft to manoeuvre from a downwind position and align with the landing runway.

This visibility value will most likely be less than that required for a straight-in approach. This is due to the normal profile for the circling approach, which is to remain at or above the circling MDA until the aircraft is established within the aerodrome’s circuit area, and then to visually circle for landing within the circuit while maintaining visual contact with the runway. Obstacle clearance is guaranteed in the normal runway circuit pattern.

The pilot may elect to descend below the circling MDA by day, but only in accordance with specific rules. In doing so the pilot takes responsibility for obstacle clearance. As spot heights on instrument approach and landing charts do not necessarily indicate the highest terrain, or all obstacles in the circling area, pilots should only exercise this option when they are familiar with the terrain in the circling area. Without detailed local knowledge, it is a safer option to utilise the obstacle protection afforded by remaining at the circling MDA until within the circuit area.

Safety analysis

On the afternoon of 22 March 2021, the pilot of VH-XGW commenced a flight from Dubbo to Bankstown. The flight was conducted under instrument flight rules and, due to the prevailing weather conditions, an instrument approach procedure was necessary to enable a landing at Bankstown Airport.

Tracking tolerance exceedance

The ATC clearance for the approach into Bankstown required the conduct of a straight-in instrument approach to runway 11C. As the aircraft passed abeam the intermediate approach fix, the aircraft was within the required half-scale deflection to be established on the approach path, enabling the pilot to commence descent on the approach. However, from that point on the aircraft progressively diverged from the required track.

Approaching abeam the final approach fix, the combination of reducing track tolerance and continued track divergence resulted in the aircraft exceeding the tolerance limit of full-scale deflection, or 0.3 NM track displacement. Significantly, this tracking error resulted in the aircraft being displaced outside of the area that had been surveyed to be clear of obstacles at an altitude of 1,100 ft, well below the Bankstown 15 NM minimum safe altitude of 2,500 ft. Further, the pilot reported that, at this point in the approach, visual flight conditions had not yet been established.

Despite those circumstances, the requirements of the instrument approach and the ATC instruction, the pilot did not conduct the published missed approach procedure.

Descent below the minimum descent altitude

Following initial acknowledgement of the ATC missed approach instruction, the pilot requested a clearance for a circling approach while continuing the descent. During the ensuing 30 seconds of communications, the aircraft descended out of the cloud and the pilot reported being visual to ATC. The pilot also advised that they checked the distance readout to Bankstown Airport and confirmed that the aircraft was within the aerodrome CAT B circling area.

At about the same time, ATC cleared the aircraft to track for final runway 11C. The pilot then initiated descent from MDA at the CAT B circling boundary with the intention of maintaining visual contact with obstacles along the intended flight path at the minimum permitted obstacle clearance height. The pilot considered that this was the safest option, given the weather conditions and the aircraft’s absence of a weather radar.

Such manoeuvring at that position was contrary to the intention of a circling approach, which is normally performed within the surveyed environment of the circuit area as part of visual circling to other than the straight‑in approach runway. More importantly, when compared to the straight-in approach descent profile, it resulted in reduced obstacle clearance, increased pilot workload and an increased risk of an unstable approach.

Loss of visual reference while below MDA

Shortly after entering the CAT B circling area, and with the pilot having reportedly established visual contact with the runway environment, the aircraft entered a rain shower. To maintain visual flight conditions, the pilot commenced a left turn away from the runway. This turn continued in to the first of two left orbits, during which the aircraft exited the CAT B circling area and descended to an altitude of around 400 ft.

The pilot stated that the aircraft was maintained within the larger CAT C circling area and that the required separation with obstacles was maintained. However, flight surveillance data indicated that the aircraft descended below the minimum altitude required to maintain separation from the terrain below the aircraft. Further, ATC was expecting the aircraft to operate within the CAT B circling limits, as stated in the flight plan, and twice during the conduct of the orbits provided terrain alerts to the pilot.

When operating below MDA, collision with terrain or obstacles are the immediate threat. The AIP and CAAP 178 stated that not all terrain and obstacles are marked on aerodrome charts. Further, the only areas where obstacle clearance is assured are those associated with the straight-in approach path, and within the circling area. Outside of these areas, separation from terrain and obstacles while below the MDA is dependent on visual acquisition and avoidance. Additionally, continuation below MDA is predicated on the pilot continuously maintaining visual reference with the runway.

Almost immediately on declaring visual, visibility deteriorated sufficiently for the pilot to initiate a turn away from the runway. The pilot stated that visual reference was only lost momentarily, however, during the left turns away from the airport, the runway environment would have been obscured by the aircraft’s structure for significant periods of time. Despite that, the pilot persisted with the approach and landing rather than conducting the published missed approach. Continuation of the approach resulted in the loss of obstacle clearance assurance and an increased risk to the aircraft occupants.

Findings

From the evidence available, the following findings are made with respect to the flight below minimum safe altitude by VH-XGW on 22 March 2021.

Contributing factors

• While conducting an instrument approach into Bankstown Airport in instrument meteorological conditions, the pilot did not conduct a missed approach when the aircraft exceeded the tracking tolerance limits. That resulted in the aircraft operating significantly below the minimum allowable altitude.
• Having descended visually below the minimum descent altitude and commenced manoeuvring to position the aircraft for a landing at Bankstown Airport, the pilot did not conduct a missed approach when the aircraft exited the circling area and the required visual reference with the runway was lost.

Safety actions

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• pilot
• Civil Aviation Safety Authority
• AIRMED Australia Pty Ltd
• Airservices Australia.

Submissions

Under section 26 of the Transport Safety Investigation Act 2003, the ATSB may provide a draft report, on a confidential basis, to any person whom the ATSB considers appropriate. That section allows a person receiving a draft report to make submissions to the ATSB about the draft report.

A draft of this report was provided to the following directly involved parties:

• the pilot
• Civil Aviation Safety Authority
• AIRMED Australia Pty Ltd
• Airservices Australia.

Submissions were received from:

• the pilot
• Civil Aviation Safety Authority.

The submissions were reviewed and, where considered appropriate, the text of the report was amended accordingly.

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through: identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. Terminology An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing information Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 2021 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence. Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work. The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

__________

1.  GPS is a United States developed Global Navigation Satellite System (GNSS).
2.  Aerodrome Forecast (TAF): a statement of meteorological conditions expected for a specific period of time in the airspace within a radius of 5 NM (9 km) of the aerodrome reference point.
3.  Eastern Daylight saving Time (EDT): Coordinated Universal Time (UTC) + 11 hours.
4.  Cloud cover: in aviation, cloud cover is reported using words that denote the extent of the cover – ‘scattered’ indicates that cloud is covering between a quarter and a half of the sky and ‘broken’ indicates that more than half to almost all the sky is covered.
5.  Instrument flight rules (IFR): a set of regulations that permit the pilot to operate an aircraft in instrument meteorological conditions (IMC), which have much lower weather minimums than visual flight rules (VFR). Procedures and training are significantly more complex as a pilot must demonstrate competency in IMC conditions while controlling the aircraft solely by reference to instruments. IFR-capable aircraft have greater equipment and maintenance requirements.
6.  The aircraft’s position and altitude data were derived from ADS-B and Mode S data transmitted to ATC by VH-XGW. ADS-B positional data was recorded in 5 second intervals. The Mode S pressure altitude data was reported to the nearest 100 ft and automatically adjusted for localised atmospheric pressure to produce an accurate altitude.
7.  QNH: the altimeter barometric pressure subscale used to indicate height above sea level.
8.  AIP ENR 1 GENERAL RULES AND PROCEDURES, section 1.1 GENERAL RULES, subsection 2 OPERATIONS IN CONTROLLED AIRSPACE, sub subsection 2.11 Descent and Approach
9.  Automatic Terminal Information Service (ATIS): The provision of current, routine information to arriving and departing aircraft by means of continuous and repetitive broadcasts during the hours when the unit responsible for the service is in operation.
10.  For the purposes of determining safety-based criteria such as landing minima for an instrument approach procedure, aircraft are separated into performance categories. These categories are based on aircraft configuration and weight criteria and the aircraft’s indicated airspeed under these conditions at the threshold when landing. CAT B covers airspeeds from 91-120 kt.
11.  The approach minima indicate that the limiting obstacles for the straight-in and circling approaches are probably 334 ft for the straight-in approach and 355 ft AMSL for the circling approach.
12.  The tolerances were derived from Civil Aviation Order (CAO) 20.91 and Civil Aviation Advisory Publication (CAAP) 179A-1(1).
13.  RNP: required navigation performance, a statement of the navigation performance necessary for operation within a defined airspace. RNP is similar to the RNAV specification, but RNP requires on board performance monitoring and alerting.
14.  An avionics instrument used for aircraft navigation. The CDI displays the aircraft’s lateral displacement in relation to a specified course to or from a radio navigation beacon, or in relation to a specified GNSS based track.
15.  Civil Aviation Order 20.91 (Instructions and directions for performance-based navigation) Instrument 2014.
16.  AIP ENR 1 GENERAL RULES AND PROCEDURES, section 1.5 HOLDING, APPROACH AND DEPARTURE PROCEDURES, subsection 1. HOLDING AND INSTRUMENT APPROACH TO LAND (IAL) PROCEDURES, sub subsection 1.21 Descent.
17.  AIP ENR 1 GENERAL RULES AND PROCEDURES, section 1.5 HOLDING, APPROACH AND DEPARTURE PROCEDURES, subsection 1. HOLDING AND INSTRUMENT APPROACH TO LAND (IAL) PROCEDURES, sub subsection 1.10 Missed Approach – Standard Procedures.
18.  AIP ENR 1 GENERAL RULES AND PROCEDURES, section 1.5 HOLDING, APPROACH AND DEPARTURE PROCEDURES, subsection 1. HOLDING AND INSTRUMENT APPROACH TO LAND (IAL) PROCEDURES, sub subsection 1.8 Visual Manoeuvring (non-Circling) Subsequent to Non-Precision Approaches (NPA) and Approaches with Vertical Guidance (APV).
19.  AIP ENR 1 GENERAL RULES AND PROCEDURES, section 1.5 HOLDING, APPROACH AND DEPARTURE PROCEDURES, subsection 1. HOLDING AND INSTRUMENT APPROACH TO LAND (IAL) PROCEDURES, sub subsection 1.7 Circling Approaches and Visual Circling.
20.  Titled Non-precision Approaches (NPA) & Approaches with Vertical Guidance (APV).

Safety summary

What happened

On the morning of 4 March 2021, the crew of a Leonardo Helicopters AW139, registered VH-PVO and operated by the Victoria Police Air Wing, were re-assigned from an aerial search near Coldstream to a search and rescue task in Orbost, Victoria. Due to the cloud conditions, the pilot upgraded the flight from visual to instrument flight rules. While en route to Bairnsdale at their cruising altitude of 5,000 ft, the helicopter entered cloud and shortly after the enhanced ground proximity warning system activated with the alert ‘caution terrain’. The pilot initiated a climbing left turn to avoid Mount Baw Baw, which had a maximum elevation of 5,138 ft.

What the ATSB found

The ATSB found that, while en route to Bairnsdale below the lowest safe altitude, the helicopter entered cloud in the vicinity of Mount Baw Baw, which resulted in activation of a ground proximity alert. The pilot identified the location of the terrain threat and conducted a climbing turn away.

The helicopter was below the lowest safe altitude as the pilot had incorrectly assessed the in-flight conditions as visual meteorological conditions after the helicopter reached 5,000 ft in the vicinity of Coldstream (based on their estimate of height above the cloud tops). As a result, the pilot elected to remain at 5,000 ft instead of recalculating the lowest safe altitude as the flight progressed.

The ATSB also found that the operator did not have a procedure for pilots when upgrading from visual to instrument flight rules in-flight. This would reduce the likelihood of an error when replanning in-flight, which was reported to be an infrequent task and higher-than-normal workload task, particularly in single-pilot operations.

What has been done as a result

After the incident, Victoria Police Air Wing developed an instrument flight rules upgrade procedure for inclusion in their operations manual. This procedure includes the acceptable methods for calculating lowest safe altitude and was circulated to all their pilots.

Safety message

This investigation highlighted the importance of lowest safe altitude calculations and to recalculate the lowest safe altitude appropriate for the area of operations.

Operators should also review their operations manual to ensure they have procedures in place to adequately capture their operating procedures in order to minimise the likelihood of decision‑making errors.

The occurrence

On 4 March 2021, at about 1120 Eastern Daylight-saving Time,^[1] the crew of a Leonardo Helicopters AW139, registered VH-PVO and operated by the Victoria Police Air Wing, were tasked with a search and rescue in Orbost, Victoria. At the time of the tasking, they were assisting with an aerial search near Coldstream. On board was the pilot and two tactical flight officers.

After receiving the new task, the crew discussed whether there was sufficient fuel onboard to continue to Orbost without returning to their base at Essendon Airport. They decided that they could proceed with the re-tasking without returning to Essendon, but would have to refuel at Bairnsdale Airport, before commencing the task at Orbost. Due to the presence of cloud to the east, in the direction of Bairnsdale, the pilot decided to upgrade the flight from visual^[2] to instrument flight rules^[3] and contacted air traffic control (ATC) accordingly.

Part of the upgrade to instrument flight rules required the pilot to calculate the lowest safe altitude^[4] (LSALT) for the flight. At the time of the upgrade, the helicopter was about 17 NM (31 km) to the north‑north-east of Moorabbin Airport. Therefore, the pilot initially calculated the LSALT of 5,000 ft above mean sea level (AMSL) based on the Moorabbin 25 NM (46 km) minimum sector altitude of 4,700 ft, with the intent to revise en route. The pilot knew they were within the 25 NM minimum sector altitude at the time as they were familiar with the area from previous training exercises. Once this was calculated and a clearance was received from ATC, the pilot set 5,000 ft as the target altitude in the autopilot altitude acquire function.

The helicopter’s forward-looking infrared camera footage recorded the helicopter entering cloud at about 2,800 ft and emerge on top of the cloud at about 4,475 ft (Figure 1), before leveling off at 5,000 ft. At interview, the pilot recalled the helicopter entered cloud at about 2,700 ft and emerged at 3,500–4,000 ft. The pilot turned the volume down on the intercom radios to focus on the other tasks associated with the upgrade, including filing a flight plan with Airservices Australia. The pilot also entered the flight path from Coldstream to Bairnsdale into OzRunways^[5] and noted they would be flying through the East Sale restricted airspace^[6] to reach Bairnsdale (Figure 2). The pilot was cognisant of the need to obtain an airways clearance for the East Sale restricted airspace early in the flight.

Figure 1: Camera footage exiting cloud at 4,475 ft on climb to 5,000 ft

Source: Victoria Police Air Wing

Figure 2: Exemplar flight plan showing the route from Coldstream to Bairnsdale

Source: The pilot, using OzRunways, annotated by the ATSB

Several minutes later, the pilot conducted the cruise checks while at 109 kt indicated airspeed^[7] and recalled that they were below LSALT as they were now outside the Moorabbin minimum sector altitude. Further, they were below the published grid LSALTs^[8] of 6,400 ft and 7,300 ft on their track to Bairnsdale (Figure 2). However, the pilot assessed that they were about 1,000 ft above a layer of cloud and that the conditions were day visual meteorological conditions,^[9] which was an acceptable reason to operate below LSALT.^[10] Based on this, the pilot decided to continue the flight at 5,000 ft and advised ATC accordingly (Figure 3).

Figure 3: Camera footage at cruising altitude above cloud at 4,998 ft

Source: Victoria Police Air Wing

The pilot turned up the intercom radio volume to communicate with the tactical flight officers about the police tasking and plan for the day. To assist the pilot, the tactical flight officer in the front-left seat entered the radio frequency for East Sale. At about 1139, the pilot made several attempts to contact the East Sale air traffic controller but was unsuccessful. The tactical flight officer checked the frequency in the En Route Supplement Australia^[11] and confirmed it was correct. Shortly after, the pilot observed the cloud tops beginning to rise while trying to verify the East Sale radio frequency, but initially believed they would pass just over the cloud tops. However, as shown on the camera footage, the helicopter entered the cloud just below the tops while the pilot was continuing to attempt to contact East Sale (Figure 4).

Figure 4: Camera footage of the rising cloud near Mount Baw Baw just prior to the ground proximity alert

Source: Victoria Police Air Wing

Upon entering the cloud, the helicopter’s enhanced ground proximity warning system (EGPWS) alert for ‘caution terrain’ activated. In response, the pilot checked the primary flight display, which depicted ‘green hash’ terrain right of track (indicating the location of the terrain hazard). Therefore, the pilot initiated a climbing left turn to the north to avoid the terrain, which was Mount Baw Baw with a maximum elevation of 5,138 ft. Shortly after commencing the climbing turn, a second ‘caution terrain’ alert activated, and the pilot continued the climbing left turn. The helicopter exited the cloud to the north of Mount Baw Baw and the camera footage revealed the sky was clear to the east. The pilot contacted ATC to request a climb to 6,000 ft and the flight continued without further incident. Figure 5 depicts the flight path with the location of Mount Baw Baw and the EGPWS alerts.

Figure 5: Map showing VH-PVO’s flight path with key locations

Source: Google Earth, annotated by the ATSB

__________

1. Australian Eastern Daylight-Saving Time: Coordinated Universal Time (UTC) + 11 hours.
2. Visual flight rules (VFR): a set of regulations that permit a pilot to operate an aircraft only in weather conditions generally clear enough to allow the pilot to see where the aircraft is going.
3. Instrument flight rules (IFR): a set of regulations that permit the pilot to operate an aircraft in instrument meteorological conditions (IMC), which have much lower weather minimums than visual flight rules (VFR). Procedures and training are significantly more complex as a pilot must demonstrate competency in IMC conditions while controlling the aircraft solely by reference to instruments. IFR-capable aircraft have greater equipment and maintenance requirements.
4. Minimum sector altitude (MSA) and lowest safe altitude (LSALT) are calculated to provide 1,000 ft obstacle clearance for IFR flights and are published on aeronautical charts and in the Aeronautical Information Publication (AIP) for pilot and controller reference.
5. OzRunways: an electronic flight bag application.
6. Restricted airspace: designated in the interests of public safety, security or for the protection of the environment to restrict the flight of aircraft over the area to aircraft flown in accordance with specified conditions.
7. Indicated airspeed is obtained from the flight data recorder.
8. Grid lowest safe altitude: the lowest safe altitude shown for a grid on an instrument flight rules chart (en route chart or terminal area chart).
9. Visual meteorological conditions (VMC): an aviation flight category in which visual flight rules (VFR) flight is permitted – that is, conditions in which pilots have sufficient visibility to fly the aircraft while maintaining visual separation from terrain and other aircraft.
10. Refer Civil Aviation Regulation 178: Minimum height for flight under I.F.R., subregulation (4)(d).
11. The En Route Supplement Australia is a publication that contains information vital for planning a flight and for the pilot in-flight.

Context

Personnel information

The pilot held an Air Transport Pilot’s Licence (Helicopter), multi-engine helicopter instrument rating, a type rating for the AW139, and Class 1 Aviation Medical Certificate. At the time of the incident, the pilot had accumulated 5,094 hours of aeronautical experience, of which 144 hours were on the AW139. The pilot had completed an instrument proficiency check in October 2020 and had recorded 5.8 hours of instrument flight in the previous 90 days, including five instrument approaches.

The pilot reported being well rested on the day of the incident. A review of the sleep and roster information obtained found there was a low likelihood the pilot was experiencing a level of fatigue known to have an adverse effect on performance.

Radar altimeter setting

As part of the ‘after-start’ checklist, the radar altimeter (RADALT)^[12] low height warning bug was required to be set to 400 ft. Around the time of the incident, there were known interference issues between the downlink from the camera and the RADALT, which could produce spurious low height RADALT indications. The pilot did not recall any spurious indications or recall referring to the RADALT during the incident flight. They also reported the low height warning bug was likely set to 400 ft as per the after-start checklist.

Recorded information

The helicopter was fitted with an enhanced ground proximity warning system (EGPWS), which would activate when terrain or obstacles were detected about 26 +/-5 seconds ahead of the helicopter. The ‘caution terrain’ alert indicated the helicopter had entered the ‘soft’ threshold for the terrain awareness mode (a ‘warning terrain’ alert would indicate the ‘hard’ threshold). The ‘green’ display reported by the pilot indicated terrain was at least 250 ft below the helicopter’s altitude.^[13] According to the helicopter’s flight manual, if a caution alert occurred in-flight, the pilot should ‘verify the aircraft flight path and correct as necessary’.

The ATSB analysed the information from the flight data recorder. Key events included:

• at 1140:11, the EGPWS alert ‘caution terrain’ activated when the aircraft was at 5,000 ft above mean sea level (AMSL) and 131 kt indicated airspeed
• at 1140:13, a pitch up and left roll were initiated after the alert
• at 1140:43 the EGPWS alert ‘caution terrain’ activated again when the aircraft was at 5,150 ft AMSL and 75 kt indicated airspeed.
• at 1140:45 a pitch up and left roll were initiated again immediately after the second alert.

At the time of the first alert, the helicopter was about 1.8 NM (3.3 km) horizontally and 200 ft above terrain. At the time of the second alert, the helicopter was within 0.8 NM (1.5 km) horizontally and 350 ft above terrain. Figure 6 depicts the flight path with terrain contours and the relative positions of the EGPWS alerts.

Figure 6: Topographic map of flight path showing time of the alerts and altitudes

Source: Google Earth and flight data recorder, annotated by the ATSB

Meteorological conditions

The Bureau of Meteorology forecast conditions for the area around Mount Baw Baw for the time of the incident were for broken clouds between 1,000 ft and 3,000 ft. Footage from the forward‑looking infrared camera on the helicopter showed that the cloud base was about 2,800 ft and the cloud tops were about 4,500 ft near Coldstream. On approach to Mount Baw Baw, the helicopter entered cloud at about 5,000 ft, which was just below the cloud tops based on the camera footage. The footage also indicated the sky was clear immediately to the east of Mount Baw Baw.

A briefing occurred at the Victoria Police Air Wing each morning, which included the weather. The pilot recalled discussing the weather at that morning’s briefing and that it was ‘average’ [clouds present] inside the Melbourne basin, but clear outside the basin. In this situation, the pilot reported their standard brief would be, ‘weather is a bit average in the basin this morning…but outside the basin it’s pretty much green [clear] everywhere so we can go anywhere outside the basin, but we might have to fly IFR [instrument flight rules]’. The pilot recalled that the forecast freezing level was above 10,000 ft on the day of the incident and therefore did not expect icing to be a factor if an IFR flight was required.

Visual meteorological conditions

For the sector from Coldstream to Bairnsdale, the helicopter started in Class C (controlled airspace) before leaving Class C and entering Class G airspace (outside controlled airspace). The following criteria apply to visual meteorological conditions (VMC) below 10,000 ft in Class C and Class G airspace:

• 5,000 m visibility
• 1,000 ft vertical separation from cloud
• 1,500 m lateral separation from cloud.

In addition, if operating in Class G airspace at or below 3,000 ft above mean sea level or 1,000 ft above ground level, whichever is highest, the minimum flight visibility was 5,000 m, remaining clear of cloud and in sight of ground or water.

Calculating lowest safe altitude under instrument flight rules

Introduction

The Victoria Police Air Wing operations manual stated that obstacle/terrain avoidance below the lowest safe altitude (LSALT) or minimum sector altitude (MSA) is a pilot responsibility unless using an air traffic services assigned level, in accordance with air traffic surveillance service terrain clearance procedures. Further, responsibility returns to the pilot when the aircraft is being flown in visual meteorological conditions.

The operations manual also outlined that minimum altitudes for IFR operations shall be from one of three methods, in accordance with Aeronautical Information Publication (AIP):

• pilot calculated
• IFR charts (terminal area chart/en route chart)
• departure and approach procedures for minimum sector altitudes and/or instrument approach landing procedures.

The AIP also stated that an aircraft must not be flown under the IFR, lower than the published lowest safe altitude or the pilot calculated lowest safe altitude, unless permitted by Civil Aviation Regulation 178 or otherwise approved by the Civil Aviation Safety Authority.

Civil Aviation Regulation 178: Minimum height for flight under I.F.R., stated that an aircraft cannot be flown below the lowest safe altitude calculated in accordance with published procedures except in accordance with subregulation (4). Subregulation (4)(d) permitted an aircraft to be flown below the lowest safe altitude if it was being flown by day in visual meteorological conditions.

Minimum sector altitude

The AIP stated that MSA was the lowest altitude that provided a minimum clearance of 1,000 ft above all objects located in an area contained within a sector of a circle of 25 NM (46 km) or 10 NM (19 km) radius centred on a significant point, the aerodrome reference point, or the heliport reference point. Moorabbin Airport had a 10 NM MSA of 3,700 ft and a 25 NM MSA in the north-east sector of 4,700 ft. As the helicopter was about 17 NM (31 km) to the north-north-east of Moorabbin Airport, the pilot requested clearance to climb to 5,000 ft as the initial cruise altitude with the intent to revise later when established on track to Bairnsdale.

Grid lowest safe altitude

The grid lowest safe altitude is the lowest safe altitude shown for a grid on an IFR chart (terminal area chart/en route chart). The AIP stated that a pilot using a grid LSALT for obstacle clearance is responsible for determining the allowance for navigation error that should be applied, considering the limitations of the navigation aids or method of navigation being used for position fixing. This navigation error allowance must be applied to the proposed track. The highest grid lowest safe altitude falling within the area covered by the determined navigation error must be used.

When the pilot loaded the flight plan into OzRunways, they were not in the vicinity of a published IFR route for the flight to Bairnsdale, so the pilot had the option to compute a pilot calculated LSALT or to use the published grid lowest safe altitude (Figure 2). The flight plan from Coldstream to Bairnsdale was across three lowest safe grid altitudes, which were 6,400 ft, 7,300 ft and 7,000 ft, with respect to the direction of travel. Therefore, the LSALT required for the route was 7,300 ft.

Instrument flight rules traffic travelling east were required to use the odd thousands of feet for their cruising levels. If the grid LSALT of 7,300 ft was selected, the flight required a cruising level of 9,000 ft to Bairnsdale to remain above LSALT and comply with the IFR cruising levels. The infrared camera footage indicated the sky was almost certainly clear at this level and icing would not have been a risk.

Pilot calculated lowest safe altitude

When the pilot upgraded the flight to IFR, air traffic control (ATC) was advised that the selected cruising level was based on the pilot calculated method for LSALT. The AIP stated that, if a route or route segment was not shown on an AIP aeronautical chart, the lowest safe altitude can be calculated by the pilot. Based on the area to be considered for RNP 2 navigation,^[14] this must be within an area of 5 NM (9 km) surrounding and including the departure point, the destination and each side of the nominal track.

Furthermore, if the highest obstacle is more than 360 ft above the height determined for terrain, the LSALT must be 1,000 ft above the highest obstacle. Otherwise, 1,360 ft must be added to the highest terrain and the LSALT rounded up to the nearest 100 ft.

This required a pilot calculated LSALT of 6,500 ft from Coldstream to Bairnsdale, to account for the peak of Mount Baw Baw at 5,138 ft, which would have permitted a cruising level of 7,000 ft in accordance with the IFR cruising levels.

Instrument flight rules upgrade in-flight

Upgrading to IFR in-flight was a relatively infrequent task. The pilot reported that it happened about once every few months. The chief pilot estimated they upgraded once or twice a year, whereas other pilots were unable to provide a frequency. The nature of Victoria Police Air Wing operations required their helicopters to conduct taskings predominantly under visual flight rules in sight of ground or water. However, the nature of the weather and terrain across Victoria required them to have the capability to transit between tasks using IFR procedures over high terrain. Prior to the incident, Victoria Police Air Wing did not have a published procedure for upgrading to IFR in-flight. The tasks involved in an upgrade to IFR would include:

• calculating the LSALT based on an applicable method
• reviewing the freezing level and risk of icing
• entering the LSALT and the destination in the navigation system
• contacting and filing a flight plan with air traffic control
• determine a method to climb to LSALT that ensures terrain clearance.

Regarding the last item, when an aircraft departs IFR from an airport, or conducts a missed approach from an instrument approach procedure, it is the compliance with the respective procedure that provides terrain clearance assurance until the aircraft reaches LSALT. Therefore, in the case of an IFR upgrade in-flight, the pilot must determine a suitable method to provide terrain clearance assurance until reaching LSALT.

Related occurrences

A review of the ATSB database found a recent similar occurrence of a helicopter entering instrument meteorological conditions while flying below LSALT.

ATSB occurrence 202002989

On 12 June 2020, a Bell 412 conducting aerial work departed Jandakot Airport, Western Australia under visual flight rules. During climb, the crew requested an upgrade to IFR and a clearance to the south-east. The crew entered cloud at 1,000 ft, which was below the minimum sector altitude of 2,500 ft. The controller issued a safety alert and cleared the helicopter to climb to 4,000 ft.

__________

12. Radar altimeter measures altitude above the terrain presently below the aircraft.
13. Yellow indicates the terrain is between 250 ft below to 500 ft above, and red indicates the terrain is at least 500 ft above the helicopter. It should be noted that the colour contours on terrain warning systems may vary across different manufacturers.
14. RNP 2 (required navigation performance) was the criteria for the Victoria Police Air Wing AW139 helicopters. It is used for en route navigation in Australia under the Performance-Based Navigation (PBN) system, which uses the global navigation satellite system (GNSS) and computerised onboard systems to define the aircraft navigation in terms of accuracy, integrity, continuity and functionality. RNP results in narrower protection areas than traditional navigation methods.

Safety analysis

Introduction

On the morning of 4 March 2021, the crew of a Leonardo Helicopters AW139, registered VH-PVO and operated by the Victoria Police Air Wing, received a ground proximity alert for ‘caution terrain’ while en route from Coldstream to Bairnsdale. As a result, the pilot initiated a climbing left turn to avoid terrain and the helicopter exited the cloud.

The analysis will discuss the calculation of the lowest safe altitude (LSALT), upgrading from visual to instrument flight rules in flight, and related procedures.

Flight into cloud below lowest safe altitude

While en route from Coldstream to Bairnsdale, the helicopter was operating at an altitude of 5,000 ft and was initially above the cloud tops. The peak of Mount Baw Baw, with an elevation of 5,138 ft, was located close to the planned track but was obscured by the formation of orographic uplift cloud for the flight path from west to east. As the required pilot calculated LSALT was 6,500 ft and the grid LSALT was 7,300 ft, the flight at 5,000 ft was below both the LSALTs available for this route. While they recognised the cloud tops were rising, the pilot initially believed the helicopter would clear the tops. This likely resulted in the pilot continuing along track, rather than requesting either a climb or diversion left/right of track, which resulted in the helicopter entering the cloud below LSALT. Almost immediately after entering cloud, the EGPWS alert ‘caution terrain’ activated. In response, the pilot identified the terrain and initiated a climbing left turn.

Assessment of in-flight conditions

As part of the instrument flight rules upgrade, the pilot was required to calculate a LSALT. The pilot used their current location and the 25 NM (46 km) Moorabbin Airport minimum sector altitude of 4,700 ft as the reason for selecting 5,000 ft. The pilot indicated this LSALT was sufficient at the time, with the intent to revise it later in-flight.

After establishing the helicopter in the cruise at 5,000 ft, the pilot completed the cruise checks, which included an altitude check. At the time, the pilot assessed the cloud tops were between 3,500 ft to 4,000 ft. Therefore, at 5,000 ft, the pilot perceived that they were about 1,000 ft above the cloud tops. Visual meteorological conditions require 1,000 ft vertical separation from cloud, which was consistent with the pilot’s assessment of the conditions at the time. Therefore, the pilot assessed that the conditions complied with the regulations permitting instrument flight below the LSALT. Based on this, the pilot decided to continue at 5,000 ft. However, recorded data from the forward-looking infrared camera indicated that the cloud tops were about 4,500 ft in the vicinity of Coldstream, and therefore the helicopter was not operating in visual meteorological conditions, which would have required the pilot to recalculate a LSALT. Therefore, the flight continued below LSALT as a result of the pilot incorrectly assessing the conditions.

IFR upgrade procedure

Although all pilots in the Victoria Police Air Wing maintain instrument ratings, the majority of the flights were operated under visual flight rules for tasking purposes. The incident pilot reported that they did not frequently upgrade from visual to instrument flight rules but needed to be prepared to do so if required by the conditions and tasking. The procedural requirements for an in-flight upgrade would therefore need to be recalled from memory while maintaining sufficient attentional resources on the task of flying and navigating the helicopter in a single-pilot environment. This results in an environment of concurrent task demands, with separate tasks competing for the pilot’s limited resources, which can increase the likelihood of a loss of awareness of the environment.

The purpose of a procedure is to provide the best way to operate the aircraft safely and efficiently by outlining the steps required to be completed at a point in time. This is a rules-based process to accomplish a task, which reduces the need to problem-solve. While the operator did not have an upgrade procedure at the time of the incident, such a procedure would incorporate both regulatory operating requirements and aircraft systems operating requirements. Therefore, a single dedicated procedure could improve the efficiency of recall, thereby reducing the cognitive task demands and likelihood of an error.

Findings

From the evidence available, the following findings are made with respect to the Flight below lowest safe altitude involving Leonardo Helicopters AW139, VH-PVO, 44 km north-north-west of Latrobe Regional Airport, Victoria, on 4 March 2021.

Contributing factors

• While en route to Bairnsdale below lowest safe altitude, the helicopter entered cloud in the vicinity of Mount Baw Baw, which resulted in activation of a ground proximity alert. The pilot identified the location of the terrain threat and conducted a climbing turn away.
• The pilot incorrectly assessed the in-flight conditions as visual meteorological conditions after the helicopter reached 5,000 ft in the vicinity of Coldstream and elected to remain at this altitude instead of recalculating the lowest safe altitude.

Other factors that increased risk

• The operator did not have a procedure for pilots when upgrading from visual to instrument flight rules in-flight. This would reduce the likelihood of an error when replanning in-flight, which is a higher-than-normal workload task.

Safety actions

Additional safety action by Victoria Police Air Wing

As a result of the incident, Victoria Police Air Wing have developed an instrument flight rules upgrade procedure to be incorporated into their operations manual. This procedure was circulated to all their pilots and included the acceptable methods for calculating lowest safe altitude and the requirement to ensure terrain clearance while on climb to that altitude.

Glossary

AGL                 Above ground level

AMSL               Above mean sea level

AIP                   Aeronautical Information Publication

ATC                 Air traffic control

CASA               Civil Aviation Safety Authority

EGPWS           Enhanced ground proximity warning system

IFR                   Instrument flight rules

MSA/LSALT      Minimum sector altitude (MSA) and lowest safe altitude (LSALT)

RADALT           Radar altimeter

VFR                 Visual flight rules

VMC                Visual meteorological conditions

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• pilot
• front and rear tactical flight officers onboard the flight
• Victoria Police Air Wing
• Bureau of Meteorology
• Airservices Australia
• Department of Defence
• Civil Aviation Safety Authority.

Submissions

Under section 26 of the Transport Safety Investigation Act 2003, the ATSB may provide a draft report, on a confidential basis, to any person whom the ATSB considers appropriate. That section allows a person receiving a draft report to make submissions to the ATSB about the draft report.

A draft of this report was provided to the following directly involved parties:

• The pilot, front and rear tactical flight officers, Victoria Police Air Wing, Airservices Australia, and the Civil Aviation Safety Authority.

Submissions were received from:

• The pilot, front and rear tactical flight officers, and Victoria Police Air Wing.

The submissions were reviewed and, where considered appropriate, the text of the report was amended accordingly.

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through: identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. Terminology An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing information Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 2021 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence. Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work. The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

Safety summary

What happened

On 18 January 2021, at 2029 Eastern Daylight‑saving Time, a Sharp Airlines Fairchild SA227 aircraft, registered VH-OZV, departed Launceston Airport, Tasmania for a scheduled freight flight to Melbourne Airport, Victoria with one pilot on board.

At 2133, the aircraft was being positioned to commence a night-time Instrument Landing System approach to runway 27 at Melbourne. While joining the approach, a turn was not commenced until after the aircraft crossed the localiser track.

After crossing the localiser track and while descending along the approach glideslope, the aircraft descended clear of cloud and the pilot sighted the runway. At that time, the aircraft was positioned slightly less than full-scale on the course deviation indicator (CDI) to the right of, and tracking away from, the localiser track. From this position, the pilot elected to continue the approach visually. However, exacerbated by a prevailing southerly wind, the aircraft continued tracking away from the localiser and, shortly after, proceeded beyond the full scale of the CDI, requiring that a missed approach be initiated. Despite that, the pilot assessed that the visual approach could be continued.

The aircraft continued to deviate from the localiser track and at 2135, reached a maximum lateral deviation of 0.55 nautical miles. The pilot then turned the aircraft further to track toward the localiser while continuing to descend. At about the same time, the Melbourne Tower air traffic controller noticed the deviation and contacted the pilot.

At 2136, at about 980 ft above mean sea level (about 583 ft above ground level), the aircraft was re‑established within full-scale CDI deflection and landed shortly after.

What the ATSB found

The ATSB found that during approach to the airport in darkness, the aircraft was not maintained within the required navigational tolerance. While that should have resulted in the conduct of a missed approach, the approach was continued with the aircraft manoeuvring significantly below the minimum safe altitude.

Safety message

Handling of approaches is one of the ATSB’s SafetyWatch priorities. Adherence to operational procedures ensures consistency of pilot action and aircraft operation during the approach and landing phases of flight. This, along with careful monitoring of aircraft and approach parameters, provides assurance that an instrument approach can be safely completed.

Most importantly, if the criteria for safe continuation of an approach are not met, the pilot should conduct a missed approach to negate the risk of colliding with obstacles or terrain.

The investigation

The occurrence

On 18 January 2021, at 2029 Eastern Daylight‑saving Time,^[1] a Sharp Airlines Fairchild SA227 aircraft, registered VH-OZV (Figure 1), departed Launceston Airport, Tasmania for a scheduled freight flight to Melbourne Airport, Victoria with one pilot on board.

Figure 1: VH-OZV

Source: Jayden Laing

At 2122, the pilot commenced descending the aircraft in darkness from the cruising altitude prior to starting an Instrument Landing System (ILS) approach (see the section titled Instrument landing system) to runway 27 at Melbourne. During the descent, and prior to commencing the approach, the aircraft entered cloud.

At 2133, as the aircraft approached the ILS localiser track from the south‑east, in preparation to intercept the localiser track, the pilot changed the autopilot mode from navigation (NAV) to heading (HDG).^[2] The selected heading, in combination with the prevailing southerly wind, resulted in a 36° intercept angle of the ILS localiser track (Figure 2).

Figure 2: Approach profile

Source: Google earth, annotated by the ATSB

The aircraft crossed the localiser track at the waypoint^[3] VISAS on a continuation of the intercept angle. After the aircraft crossed the localiser track, the pilot reselected NAV mode to commence the intercept and establish the aircraft on the inbound track. However, the autopilot‑commanded turn toward the localiser track did not occur as quickly as the pilot anticipated so HDG mode was again selected with a commanded heading of 250° magnetic. Soon after selecting HDG mode, the aircraft approached the ILS glideslope. The pilot reported that the aircraft was still within half scale of the localiser course deviation indicator (CDI) so commenced descending along the glideslope and extended the landing gear.

Shortly after intercepting the glideslope, the aircraft descended clear of the cloud base at about 2,000 ft above mean sea level (AMSL) and the pilot sighted the runway. At that time, the aircraft was positioned slightly less than full-scale CDI deflection to the right of the localiser track and diverging away at an angle of about 9°. From this position, the pilot elected to continue the approach visually (see the section titled Night visual approach criteria and Figure 2). The pilot did not advise air traffic control (ATC) that the approach was continuing visually and was not cleared by ATC to conduct a visual approach. Had a visual approach clearance been provided, the pilot would have been required maintain the aircraft within full-scale CDI deflection and above the glideslope.

The aircraft continued tracking away from the localiser with the autopilot in HDG mode. Shortly after the pilot had elected to continue visually, about 6.8 NM from the runway 27 threshold, the aircraft proceeded beyond the full scale of the CDI. The pilot reported that they did not observe the CDI exceed full-scale deflection.

The aircraft continued to deviate from the localiser track. At 2135:17, the aircraft reached a maximum lateral deviation of 0.55 nautical miles (NM) and the pilot disconnected the autopilot to manually intercept the track. At about the same time, ATC personnel in both the Melbourne Airport control tower and Melbourne air traffic control centre observed the aircraft deviating to the north of the localiser track. The tower controller notified the pilot of the deviation and the pilot responded ‘adjusting’. A few seconds later, the aircraft reached a maximum angular deviation from the localiser track of 4.92° at about 1,680 ft AMSL.

The pilot then turned the aircraft further to track toward the approach track as it descended. At 2136:20, at about 980 ft AMSL (about 583 ft above ground level), the aircraft was re‑established within full scale CDI deflection.

The aircraft did not significantly deviate from the ILS glideslope angle during the approach and landed at 2137:39. No defect with the autopilot system or navigation instrumentation was identified after the occurrence.

Meteorology

At 2130, shortly before the approach, the Bureau of Meteorology (BoM) automatic weather station at Melbourne Airport recorded the wind being 18 kt from 228° magnetic. Three cloud layers: Few^[4] at 2,034 ft, Scattered at 2,634 ft, and Broken at 3,634 ft AMSL were also present.

Instrument landing system

An Instrument Landing System (ILS) is an instrument approach procedure that provides lateral (localiser) and vertical (glideslope) position information necessary to align an aircraft with the runway for approach and landing. The system uses angular deviation signals from the glideslope antennas (located approximately 1,000 ft from the runway threshold) and the localiser antennas (located past the far end of the runway).

The localiser signals provide the angular deviation from the runway centreline, which in VH-OZV were presented as fly-left or fly-right commands on the CDI. A pilot or the autopilot (in NAV mode) follows these commands to track the localiser centreline. Localiser deviation was displayed in units of dots, where typically full-scale deflection (5 dots) equates to 105 m deviation from the localiser centreline at the runway threshold.

The glideslope signals provide the angular deviation from the nominal glideslope (usually 3°) which were presented as fly-up or fly-down commands on the glideslope indicator to follow the glideslope to the decision altitude.

For both the localiser and glideslope, no additional deviation indications are provided beyond full scale indicator deflection.

Minimum sector altitude

The ILS approach chart (Figure 3) included minimum sector altitudes (MSAs) that provided a minimum terrain clearance of 1,000 ft above all objects located inside a defined area. Within a 10 NM radius of Melbourne Airport, the MSA was 3,300 ft AMSL.

Figure 3: Melbourne Airport runway 27 ILS approach chart

Source: Airservices Australia

Night visual approach criteria

Relevant guidance for the conduct of an instrument approach at night in controlled airspace is provided in sections 1.1 and 1.5 of the Aeronautical Information Publication (AIP) En Route:

En Route 1.1:

- Paragraph 2.11.2.1 ATC Authorisation

Unless authorised to make a visual approach, an instrument flight rules (IFR) flight must conform to the published instrument approach procedure nominated by ATC.

- Paragraph 2.11.3.7 Minimum Altitude Requirements

During the conduct of a visual approach, a pilot must descend as necessary to:

…b. by night:

(1) for an IFR flight:

Maintain an altitude not less than the route segment MSA…until the aircraft is:

…within 10 NM of the aerodrome, established not below the ILS glide path with less than full scale azimuth deflection.

En Route 1.5:

- Paragraph 1.10 Missed Approach – Standard Procedures

(1) A missed approach must be executed if:

during the final segment of an instrument approach, the aircraft is not maintained within the applicable navigation tolerance for the aid in use.

Safety analysis

At about 2133, the aircraft was descending toward Melbourne Airport prior to commencing a night- time ILS approach to runway 27. The intercept of the ILS localiser track did not begin until after the aircraft had already crossed that track at an angle of about 36°. The southerly wind acting on the westbound aircraft resulted in it quickly deviating to the right of the localiser track.

While the aircraft continued deviating right of the track, as long as it was within the full-scale CDI deflection, the pilot was permitted to continue the ILS approach visually only with ATC authorisation. As this authorisation was not requested and provided, the pilot was required to adhere to the tracking tolerances of the ILS approach.  Therefore, once the aircraft tracked beyond full-scale localiser CDI deflection, the pilot was required to conduct the published missed approach procedure.

The pilot reported that they did not observe the CDI exceed full-scale deflection, instead assessing that the visual approach could be continued. Continuing the approach took the aircraft significantly beyond the localiser tracking tolerance at altitudes as low as 980 ft AMSL (2,320 ft below the minimum sector altitude).

As the incident took place at night, the pilot’s ability to visually identify obstacles was limited. The continuation of the night approach outside of the localiser tolerance and below the minimum sector altitude was contrary to the required approach requirements. This in turn removed obstacle clearance assurance, increasing the collision risk to the flight.

Findings

From the evidence available, the following findings are made with respect to the flight below minimum altitude involving Fairchild SA227, VH-OZV 9 km east of Melbourne Airport, Victoria on 18 January 2021.

Contributing factors

• During approach to the airport in darkness, the aircraft was not maintained within the required navigational tolerance. While that should have resulted in the conduct of a missed approach, the approach was continued with the aircraft manoeuvring significantly below the minimum safe altitude.

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• operator
• pilot
• Airservices Australia
• Bureau of Meteorology

Submissions

Under section 26 of the Transport Safety Investigation Act 2003, the ATSB may provide a draft report, on a confidential basis, to any person whom the ATSB considers appropriate. That section allows a person receiving a draft report to make submissions to the ATSB about the draft report.

A draft of this report was provided to the following directly involved parties:

• operator
• pilot
• Airservices Australia
• Civil Aviation Safety Authority

No submissions were received on the draft report.

Purpose of safety investigations The objective of a safety investigation is to enhance transport safety. This is done through: identifying safety issues and facilitating safety action to address those issues providing information about occurrences and their associated safety factors to facilitate learning within the transport industry. It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. Terminology An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing information Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 2021 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence. Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work. The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

__________

1.  Eastern Daylight saving Time (EDT): Coordinated Universal Time (UTC) + 11 hours.
2.  In NAV mode, the autopilot system follows the lateral path commanded by the ILS localiser. When HDG mode is selected, the autopilot steers the aircraft according to a heading manually selected by the pilot.
3.  Waypoint: A defined position of latitude and longitude coordinates, primarily used for navigation.
4.  Cloud cover: in aviation, cloud cover is reported using words that denote the extent of the cover – ‘few’ indicates that up to a quarter of the sky is covered, ‘scattered’ indicates that cloud is covering between a quarter and a half of the sky, ‘broken’ indicates that more than half to almost all the sky is covered, and ‘overcast’ indicates that all the sky is covered.

Overview of the investigation

On 8 May 2019, the ATSB commenced an investigation into the descent below minimum safe altitude involving a Regional Express Saab 340B aircraft, registered VH-OLM which occurred 15 km south-west of Williamtown Aerodrome (Newcastle Airport), New South Wales, on the evening^[1] of 28 March 2019, at about 1942 Eastern Daylight-saving Time.^[2]

As part of the investigation, the ATSB interviewed the aircraft flight crew and Williamtown Aerodrome air traffic controllers. The operator’s Route Manual was examined for information relating to the conduct of visual approaches and specific information about the operation of flights into Williamtown. The ATSB also reviewed Airservices Australia’s requirements of the conduct of visual approaches^[3] and the required segment minimum safe altitude at Williamtown Aerodrome.^[4]

Air traffic control (ATC) cleared the flight crew to conduct a visual approach via a right base circuit leg to runway 12, and told the flight crew to report once they were ‘on base’. The aircraft had descended to 900 ft when the flight crew contacted ATC to report that they were on base. The controller then looked for the aircraft again and observed that the aircraft was further away than the expected position (about 4.7 NM south of the airport) and according to the radar display, below the segment minimum safe altitude. The controller then issued a safety alert and instructed the flight crew to climb. The flight crew complied with the instruction to climb. The aircraft landed without further incident.

The ATSB found the flight crew had misjudged the aircraft’s position relative to the aerodrome while conducting a night visual approach.

ATSB comment

Based on a review of the available evidence, the ATSB considered it was unlikely that further investigation would identify any systemic safety issues. Consequently, the ATSB has discontinued this investigation.

The evidence collected during this investigation remains available to be used in future investigations or safety studies. The ATSB will monitor for any similar occurrence that may indicate a need to undertake a further safety investigation.

__________

1. The approach started five minutes before the end of nautical twilight.
2. Eastern Daylight-saving Time (EDT) was Coordinated Universal Time (UTC) + 11 hours.
3. Aeronautical Information Publication, 28 February 2019, Airservices Australia.
4. DME or GNSS Arrival Procedures Williamtown, NSW (YWLM), 28 February 2019, Airservices Australia.

On 6 August 2017, an Airbus A320, registered VH-VGY and operated by Jetstar Airways, inadvertently descended below a 2,500 ft minimum safe altitude during an arrival procedure into Christchurch, New Zealand.

As the incident occurred in New Zealand, under paragraph 5.1 of Annex 13 to the Convention on International Civil Aviation and in accordance with the New Zealand Transport Accident Investigation Commission Act 1990, the Transport Accident Investigation Commission (TAIC) commenced an investigation into the occurrence. The Australian Transport Safety Bureau (ATSB), representing the state of the operator and in accordance with paragraph 5.18 of Annex 13, provided an accredited representative to participate in the TAIC inquiry. In accordance with the Australian Transport Safety Investigation Act 2003, an ATSB investigation was commenced to support the TAIC inquiry.

The ATSB has finalised its support of this investigation. The TAIC is responsible for the release of the final investigation report into this incident. TAIC have completed the investigation and published the investigation on their website on 2 May 2019 at  AO-2017-007.

Any enquires regarding the TAIC investigation and report should, in the first instance, be directed to the:

Transport Accident Investigation Commission
Level 9, 114 The Terrace
PO Box 10323
Wellington, 6143, New Zealand

The TAIC can also be contacted via: www.taic.org.nz

___________
The information contained in this update is released in accordance with section 25 of the Transport Safety Investigation Act 2003.

What happened

On 18 November 2017, the flight crew of a Boeing 777-319(ER) aircraft, registered ZK-OKN and operated by Air New Zealand, was conducting a scheduled passenger service from Auckland, New Zealand, to Brisbane, Queensland. The flight crew consisted of the aircraft captain, who was the pilot flying (PF), and the first officer, who was the pilot monitoring (PM).^[1]

The flight crew commenced duty at 0525 Eastern Standard Time,^[2] and the aircraft departed Auckland at 0630. As the aircraft approached descent into Brisbane, the flight crew copied the expected arrival procedures and weather conditions from the ATIS.^[3] The ATIS, information ‘OSCAR’ (O), stated that arriving aircraft were to expect an instrument approach to runway 01,^[4] and that the wind at the threshold of runway 01 was 180° at 5 kt, with a maximum tailwind of 5 kt. The flight crew programed and briefed for an expected SAVER1P standard arrival procedure with an RNAV-P (RNP) RWY 01 approach. The PF reported that, in response to the expected tailwind on final approach and landing, the approach briefing included the importance of ensuring that the aircraft did not get high during the descent and approach.

Prior to commencing the descent, the aircraft was cleared to conduct a SAVER1A standard arrival procedure for an ILS approach to runway 01 (Figure 1).The flight crew reprogrammed and re-briefed the arrival before commencing the descent.

Figure 1: An extract of the Jeppesen SAVER1A chart

The aircraft’s quick-access recorder (QAR)^[5] provided information on the aircraft’s flight parameters, autoflight system altitude targets, and autoflight system modes. During the descent, the aircraft was being controlled by the PF through the use of an autopilot, with flight profile changes being achieved through selections on the mode control panel (MCP) (see Figure 2). Under normal procedures, the flight crew were required to verify autoflight system mode changes, such as those selected on the MCP, had been activated through the required mode being displayed on the flight mode annunciator (FMA). The FMA, located just above the primary flight display (see Figure 2), displayed the active flight modes for, from left to right, the autothrottle, roll and pitch.

Figure 2: Flight deck panels identifying the mode control panel with associated controls, and the primary flight display with the flight mode annunciator expanded.

Source: Boeing, annotation by ATSB.

The aircraft commenced descent at 0856 with the autopilot selected on and the autoflight system being selected to the LNAV and VNAV modes.^[6] Approaching DUNNI, at 0919 with a descent clearance limit of 5,000 ft, air traffic control (ATC) cleared the aircraft to continue the descent to 4,000 ft. In response, the PF set 4,000 on the MCP and the aircraft continued the descent while tracking towards VETIS. At about 0921:15, a change of controllers commenced at the ATC workstation. The handover to the new controller was completed at about 0922:30. During this period the aircraft was approaching VETIS, and the flight crew reported that they were keen for further descent, being mindful of the desire to ensure that the aircraft did not get high on the descent.

Shortly after passing VETIS, at 0922:45, and while maintaining 4,000 ft, ATC cleared the aircraft to descend to 3,000 ft and for the ILS runway 01. The PF selected 3,000 ft in the MCP altitude window (see Figure 3 at 0922:52) and pressed the altitude selector^[7] to initiate further descent. The PF later observed that the altitude selector was probably not properly pressed. As a result, the expected flight mode change did not occur and the aircraft did not commence the descent as expected. The QAR data recorded the autoflight pitch remaining in the VNAV mode, however, the flight crew later reported that the VNAV mode changed from VNAV PTH to VNAV ALT. The PF reported that this pitch mode change was unexpected and unfamiliar. The flight crew operations manual stated the following with respect to the pitch mode entering VNAV ALT:

When a conflict occurs between the VNAV profile and the MCP altitude, the airplane levels and the pitch flight mode annunciation becomes VNAV ALT. The airplane maintains altitude. To continue the climb or descent, change the MCP altitude and push the altitude selector or change the pitch mode.

In response, and with the intent of ensuring that the aircraft did not get high on the desired descent profile, the PF selected the V/S^[8] mode, and then the FLCH^[9] mode, to initiate the descent. The aircraft commenced descending and at 0923:33 the autoflight system commenced reducing the rate of descent to capture the cleared altitude of 3,000 ft—indicated by the ALT^[10] mode activating. Shortly after, and as the aircraft passed through LOGAN, the autoflight system transitioned back into the VNAV mode and then the ALT mode.

Figure 3: Flight data for the period 0922.45 (at about VETIS) to 0925.00 (just before GLENN).

Source: ATSB

As the aircraft was turning towards GLENN, and maintaining the cleared altitude of 3,000 ft, the PF selected 1,000 ft in the MCP and then the FLCH mode with the intent of continuing the descent further. About 5 seconds later, at 0924:03, the aircraft commenced descent from 3,000 ft. At 0924:14, as the aircraft had passed 2,850 ft, ATC instructed the aircraft to maintain best speed, and at least 180 kt until 5 NM final. The PM acknowledged the instruction.

At 0924:35 the PF raised the MCP target altitude to 2,000 ft and changed the flight mode to V/S. At 0924:50, ATC alerted the aircraft that it was cleared to 3,000 ft and that it was descending through 2,200 ft, which was acknowledged. The aircraft levelled at about 2,000 ft and maintained that altitude until it intercepted the glideslope for the ILS. The aircraft landed at 0929 without further incident.

Pilot comments

The PF later reported that, as a result of not properly pressing the altitude select push button to commence the descent from 4,000 ft, the workload experienced increased significantly. This resulted in what the PF described as a loss of situational awareness. After being alerted by ATC that the aircraft was below the cleared altitude of 3,000 ft, and at that time having the runway in sight and being able to maintain visual conditions until landing, the PF decided to maintain 2,000 ft until the aircraft re-joined the approach profile to reduce the workload.

The PM reported that the PF’s actions in descending below the cleared level were not challenged, as this was the first time that the PM had flown this approach.

Operator’s comments

The crew underwent a training session in the B777 simulator to replicate the event and to identify how the error was able to manifest. The training also represented an opportunity to reinforce the use of the various modes for the approach phase.

The RNAV approaches are regularly treated as step down approaches by controllers. The RNAV approaches were designed to reduce pilot and controller workload, however, they regularly increase the pilot workload and increase the opportunity for crew errors. It is also not uncommon to be taken off an RNAV path, given radar vectors then put back on the RNAV at some point in the RNAV path sequence which also increases pilot workload.

Related occurrences

A number of ATSB investigations have examined occurrences that included altitude deviations in flight path involving foreign crew operating within Australia. Of these, two recent examples are summarised below. Full reports are available at the ATSB website.

ATSB investigation AO-2017-026

On the morning of 22 February 2017, a Singapore Airlines Boeing 777-212, from Singapore Changi Airport, Singapore, to Canberra Airport, Australian Capital Territory, was conducting a standard arrival into Canberra when it descended through an altitude constraint associated with the arrival procedure. The error was the result of FMC entry omissions and the flight crew not identifying the relevant altitude limitation.

ATSB investigation AO-2016-012

During a second approach into Perth Airport, Western Australia, an Airbus A320 aircraft operated by PT Indonesia AirAsia was conducting a VOR approach to runway 06 when the flight crew descended the aircraft earlier than normal, but believed that they were on the correct flight path profile. While descending, both flight crew became concerned that they could not visually identify the runway, and focused their attention outside the aircraft. At about that time, the approach controller received a ‘below minimum safe altitude’ warning for the aircraft. The controller alerted the crew of their low altitude and instructed them to conduct a go-around.

Safety analysis

The approach and landing are phases of flight known to have high workload. That workload can increase exponentially when errors and the unexpected occur. As a result of not pressing the altitude selector properly, and then checking that the required flight mode change occurred on the FMA, the PF’s workload increased substantially. This resulted in the PF losing awareness of the aircraft’s descent profile, and in particular the aircraft’s altitude versus the distance to landing, a component of what is commonly referred to as situational awareness. This loss of descent profile awareness, combined with a preconception that the aircraft should not get high on profile during the positioning for final approach, resulted in the PF initiating a descent below the altitude limit of 3,000 ft that was required to be maintained until the aircraft was established on final approach. The PF identified the error and began levelling the aircraft just before the flight crew were notified by ATC that the aircraft had breached the descent clearance limit.

The PM role requires an awareness of the PF actions as well as an awareness of the aircraft’s flight profile relative to the clearance limit and any limitations associated with the approach procedure. While the PM had not flown this approach before, the monitoring role during the approach was not effectively executed.

Findings

These findings should not be read as apportioning blame or liability to any particular organisation or individual.

• As a result of high workload, a loss of awareness of the aircraft’s descent profile, and a preconception with ensuring that the aircraft did not get high on the approach flight path, the flight crew initiated a descent below the cleared altitude of 3,000 ft as the aircraft was positioning for final approach. The flight crew corrected the error and levelled the aircraft at about 2,000 ft shortly before being alerted of the altitude breach by ATC.

Safety message

This investigation identifies how an error can increase workload, particularly during a phase of flight that has an already high workload. It also highlights the importance of confirming mode changes on the FMA. Handling of approaches to land continues to be a safety priority for the ATSB.

About this report Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, a limited-scope, fact-gathering investigation was conducted in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions. Publishing information  Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 2018 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence. Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work. The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

__________

1. Pilot Flying (PF) and Pilot Monitoring (PM): procedurally assigned roles with specifically assigned duties at specific stages of a flight. The PF does most of the flying, except in defined circumstances; such as planning for descent, approach and landing. The PM carries out support duties and monitors the PF’s actions and the aircraft’s flight path.
2. Eastern Standard Time (EST): Coordinated Universal Time (UTC) + 10.0 hours.
3. Automatic terminal information service, a continuous and repetitive broadcast that provides current, routine information to arriving and departing aircraft. That information normally includes current meteorological conditions at the airfield, as well as expected approach requirements.
4. Runway number: the number represents the magnetic heading of the runway.
5. A QAR is an airborne flight data recorder that provides quick and easy access to raw flight data. QARs provide a limited scope of flight data. The QAR data did not identify which autopilot was engaged, nor the specific component of VNAV that was the active mode.
6. The lateral navigation (LNAV) and vertical navigation (VNAV) modes command the autoflight system to follow the flight management system generated optimum lateral and/or vertical navigation flight path. VNAV is a general descriptor for three sub-component modes, VNAV PTH, VNAV SPD and VNAV ALT. QAR pitch data only identified that VNAV was active, not the specific component.
7. With the aircraft in level flight, in VNAV PTH or VNAV ALT pitch modes, and the selected altitude as displayed in the altitude window being below the current altitude, pushing the inner altitude selector will result in the aeroplane commencing a descent to the selected altitude.
8. The vertical speed mode, an autoflight mode that enables the flight crew to command a desired rate of climb or descent from the autoflight system.
9. Flight level change mode, an autoflight mode that enables the flight crew to command an immediate climb or descent to the target altitude as selected in the altitude window, without reference to any flight management system altitude or speed constraints.
10. The altitude hold mode (ALT) is activated by either pushing the MCP altitude HOLD switch, or capturing the selected altitude from a V/S, FPA, or FLCH climb or descent.

What happened

On 27 October 2017, at 1410 Eastern Daylight-savings Time (EDT),^[1] a captain and first officer signed on for flight duty at Brisbane Airport, Queensland. The planned duty was to operate a JetGo Embraer ERJ135 aircraft, registered VH-ZJG, on four scheduled passenger transport sectors: from Brisbane to Dubbo, New South Wales, Dubbo to Essendon, Victoria, Essendon to Dubbo, and Dubbo to Brisbane.

The aircraft was scheduled to depart Brisbane at 1510. However, the flight crew were advised of an engineering delay of up to 45 minutes for unscheduled maintenance to change a main landing gear tyre. A replacement tyre was not immediately available, which resulted in an extended delay that eventually totalled 4 hours 15 minutes.

The aircraft departed Brisbane at 1925 and, after an uneventful flight, departed Dubbo for Essendon at 2116. The first officer was the pilot flying (PF) and the captain was the pilot monitoring (PM) for the sector from Dubbo to Essendon.^[2]

Prior to commencing descent, the flight crew programmed the aircraft’s flight management guidance system and briefed for an instrument landing system^[3] (ILS) approach to runway 26. It was the first time either pilot had operated into Essendon at night, and therefore their preferred approach was a runway 26 ILS approach. The flight crew also discussed the possibility of receiving radar vectors^[4] from air traffic control (ATC).

ATC informed the flight crew that due to aircraft traffic at neighbouring Melbourne Airport, runway 26 was unavailable. Therefore, ATC provided radar vectors for a visual approach to runway 35. As the aircraft passed abeam Melbourne Airport, the captain had Melbourne and Essendon runways in sight.

At 2220:18, ATC advised the flight crew that they would be positioned for a 5 NM (9.3 km) final approach at 2,100 ft above mean sea level (AMSL). This altitude was the radar lowest safe altitude for that sector of airspace. At 2221:48, ATC instructed the flight crew to descend to 2,100 ft.

The first officer recalled setting 2,100 ft on the aircraft’s altitude preselector. This directed the automatic flight control system (AFCS) to continue descent to 2,100 ft. He also recalled confirming the 2,100 ft set altitude on his primary flight display, as well as the flight director modes of heading and vertical speed mode. The captain recalled verifying the assigned altitude being set and flight director modes. Both flight crew recalled the autopilot was engaged at this time.

At 2223:02, as the aircraft passed about 2,300 ft on descent, ATC requested the flight crew to report sighting runway 35. At this time, the captain had lost sight of the runway. Becoming concerned that the captain could not visually identify the runway, the first officer also focused his attention looking outside the aircraft to the left to help locate the airport.

At about 2223:35, when 7.1 NM (13.1 km) from Essendon Airport and on a heading of 080°, the aircraft descended below the assigned altitude of 2,100 ft. Neither flight crew detected the aircraft was now below the radar minimum safe altitude and continuing to descend. When the captain next looked inside the aircraft at his primary flight display, he recalled seeing the altimeter indicating 1,600 ft, and he then called ’height’. The first officer also recalled seeing that they were below the assigned altitude at the same time.

At 2223:52, ATC instructed the flight crew to climb to 2,100 ft. However, that instruction was over transmitted by another aircraft and not heard by the flight crew. At 2223:58, ATC issued another instruction to climb immediately to 2,100 ft, which the flight crew acknowledged.

At 2224:05, a cleared level adherence monitoring (CLAM) alarm^[5] activated (Figure 1), further alerting ATC of a difference between the aircraft’s assigned altitude and its actual altitude. ATC immediately issued a terrain safety alert, advising the flight crew that the lowest safe altitude was 2,100 ft.

Recorded radar data showed the aircraft’s lowest altitude was about 1,500 ft during 2224:05 to 2224:10 (Figure 1).

Figure 1: Image of air traffic controller’s monitoring screen showing CLAM alarm activation following the aircraft’s descent below 2,100 ft

Image shows the aircraft (JG044) with a current altitude of 1,500 ft (‘015’), a cleared altitude of 2,100 ft (‘021’), a radar vectored heading of 070° (‘H070’) and a groundspeed of 160 kt (‘16’).

Source: Airservices Australia

As the aircraft climbed above 2,100 ft, ATC advised the flight crew of their position relative to runway 35 and asked if they had the runway in sight. When they confirmed that they did, ATC asked if they wanted to continue the approach. The flight crew elected to discontinue the approach and ATC subsequently vectored the aircraft for another approach. The aircraft landed without further incident at 2236.

At 2259, the aircraft taxied for departure from Essendon and then completed the service to Dubbo and Brisbane. The flight crew finished duty in Brisbane at 0245.

Airport information

Essendon Airport is located about 8 km south-east of Melbourne Airport. The proximity of the two airports adds complexity to operations at Essendon.

The airport has two runways aligned 17/35 and 08/26, and it is bounded on two sides by freeways with substantial amber lighting and well-lit residential areas. At night, the lights around the airport present a complex picture. The published aerodrome chart had a caution note describing that amber freeway lighting may confuse flight crews when attempting to identify runway 08/26 lighting.

Runway 35 did not have an instrument approach procedure. Instead, pilots were required to conduct visual approaches to this runway. It was equipped with a precision approach path indicator light (PAPI) array to provide pilots with vertical profile guidance during visual approaches.

At the time of the occurrence, visibility was greater than 10 km, and the wind was a northerly at 14 kt.

Essendon Airport had a curfew prohibiting aircraft movements from 2300 until 0600 for all operations other than emergency services. Operators would incur financial penalties for flights arriving or departing during the curfew period.

To continue the service from Essendon to Dubbo (and then Brisbane), the aircraft had to commence taxiing for departure before the curfew. Missing curfew would result in the aircraft being grounded until 0600 the next morning, disrupting the current service and that of the following day.

The aircraft taxied for the return flight from Essendon at 2259, 1 minute before the commencement of the curfew period. Both flight crew reported feeling significant pressure to complete the service and return the aircraft to Brisbane. Both pilots reported being aware of the potential problem with the curfew prior to departing Brisbane, and the first officer reported considering the potential problem with the curfew during the visual approach into Essendon.

Air traffic control information

Airservices Australia provided an ATC service to the aircraft for the entire flight, including the descent to Essendon. The approach controller who provided radar vectors to the flight crew was also responsible for sequencing a large number of aircraft arrivals into Melbourne at the same time.

In an effort to manage the risk that neither pilot had operated at night into Essendon, the captain’s preferred arrival was to runway 26 as it was equipped with an ILS and was the longer runway. However, due to the congestion of arriving and departing aircraft at Melbourne, ATC advised this request was not available. Although the captain maintained the ability to instruct ATC that he required the ILS approach, he was likely aware that doing so would possibly result in ATC needing the aircraft to enter a holding pattern until the controller could sequence the flow of aircraft traffic at both airports.

When conducting a visual approach to a runway, ATC can provide radar vectors to the pilot until the aircraft is aligned with the runway centreline. A pilot is required to report that they have sight of, and can maintain sight of, the landing runway in order for ATC to clear a pilot to conduct the approach.

The flight crew reported that during the radar vectoring towards Essendon, they felt pressure from ATC to sight runway 35. The ATSB reviewed audio recordings between the approach controller and the flight crew. The flight crew first contacted Melbourne Approach at 2213:58. At 2223:02, the approach controller asked them to report Essendon runway 35 in sight. This was the only recorded request made by the approach controller to the flight crew to sight runway 35.

Automatic flight control system

Flight crews normally manage flight of an ERJ135 using the aircraft’s AFCS. This system consists of dual autopilots, a flight guidance controller (FGC) and flight instrument displays.

To manage the aircraft in all flight phases, pilots select various modes on the FGC. Selected descent modes included flight level change, speed hold and vertical speed.

The pilot can engage the autopilot by pressing a button on the FGC. Intentional disengagement of the autopilot by a pilot generates an audible voice AUTOPILOT alert. Failure and disconnection of an autopilot results in the same audible voice alert and generates a warning message illuminated on a separate indicating system.

In the ‘vertical speed’ (VS) selected descent mode, the AFCS will maintain a selected vertical speed. The rate of vertical speed can be changed as needed by the pilot. With the autopilot engaged, the VS mode would automatically change to altitude capture mode as the aircraft approached a preselected altitude.

An ‘altitude preselect’ (ASEL) mode armed automatically if the aircraft climbed or descended towards a preselected altitude. Altitude preselect mode would then automatically capture and cancel any existing mode at an appropriate point based on preselected altitude error and vertical speed. The system would then automatically switch to altitude hold mode after the aircraft had levelled off at the preselected altitude.

The first officer recalled selecting the descent mode to vertical speed at the time ATC commenced issuing radar vectors. The flight crew reported that the autopilot was engaged during the descent and that the AFCS failed to capture the preselected altitude (2,100 ft) as expected. Further, the flight crew recalled that no alert was heard, either for autopilot disconnect or altitude exceedance, which should have sounded when the aircraft was 200 ft below the preselected altitude.

After descending below 2,100 ft, the flight crew reported that the flight director pitch bars, which indicate the direction of the preselected altitude, were providing guidance that the aircraft should climb.

The ATSB requested the aircraft’s flight data recorder. However, at the time of the request, the data for the occurrence flight had been overwritten.

Following the flight, no technical log entry was made regarding a problem with the autopilot capturing the selected altitude. Nevertheless, an engineering inspection of the AFCS was conducted following the aircraft’s arrival back in Brisbane, and no fault was found.

The flight crew advised that they were aware of other recent AFCS problems associated with the aircraft and the operator’s other ERJ135 aircraft. A review of maintenance records for the operator’s ERJ135 fleet identified that several AFCS-related problems had been reported during the period from 3 August. However, none of those problems were similar to what occurred during the occurrence flight. In addition, no subsequent problems that were similar in nature were reported on the occurrence aircraft.

Flight crew information

The captain held an Air Transport (Aeroplane) Pilot Licence (ATPL) and had 10,100 hours total flight experience, including 155 hours on the aircraft type. The first officer held a Commercial (Aeroplane) Pilot Licence and had 2,100 hours total flight experience, including 473 hours on type.

Both flight crew had operated into Essendon on many previous occasions, but neither had operated to that airport at night.

Flight and duty times

The captain had the two previous days (2526 October) rostered off duty, and had conducted administrative work from 10001600 on the 24 October. The first officer had the four previous days rostered off duty.

On the day of the occurrence, both flight crew signed on to commence duty at 1410 EDT. Due to the delay before the first flight, they ultimately signed off duty at 0245, a duty period of 12.6 hours. However, the captain advised that he commenced administrative duties, unrelated to the subsequent flights, at about 1200 EDT. Therefore, his actual duty time was 14.8 hours.

The captain recalled waking up at about 0700 EDT on the day of the occurrence after a ‘normal’ sleep. He therefore had been awake for 15.4 hours at the time of the occurrence, and 18.8 hours at the end of the extended duty period. The first officer recalled waking up at 0630 EDT on the day of the occurrence after a ‘reasonable’ sleep, and was therefore awake for 15.9 hours at the time of the occurrence and 19.3 hours at the end of the extended duty period.

The operator managed its flight crews’ flight and duty times to comply with a standard industry exemption to Civil Aviation Order (CAO) 48.0, which was issued to the operator by the Civil Aviation Safety Authority (CASA). The exemption stated that duty included any task associated with the business of an operator.

The operator’s rostering personnel managed flight crew flight and duty times in order to comply with the exemption. The operator’s procedures required that all work-related activities for the operator be reported and considered as duty time.

The rostered flight duty limit for a pilot signing on after 1300 local time for a four-sector duty was 12 hours. However, a pilot could elect to extend a duty already started for up to 2 hours as long as they felt mentally and physically fit to continue (and they submitted a report upon completing the duty). Although the captain’s recorded duty time did not exceed 14 hours by the end of the trip, the actual duty time did exceed the limit.

During the delay on the ground in Brisbane, the crew were offered an option to stand down as they were now facing a long duty period. The captain reported that he was told his standing down would mean his four scheduled flights that day would be cancelled as there were no replacement captains available. Both pilots reported feeling fit to continue and elected to continue the flights. However, the captain later reported that he felt some pressure to operate the flights. The cabin crewmember stood herself down and was replaced.

Safety analysis

During radar vectoring to runway 35 at Essendon Airport, the aircraft descended below the radar minimum safe altitude of 2,100 ft. The flight crew reported that the autopilot was engaged and the altitude of 2,100 ft was preselected at the time of the occurrence. A subsequent engineering inspection found no fault with the AFCS. Because no flight data was able to be obtained, the ATSB was unable to confirm what the AFCS mode(s) and settings were at the time of the occurrence, or the reason why the aircraft descended below the preselected altitude.

Regardless of the reason for the aircraft descending through the prescribed altitude, flight crew have a vital role in monitoring the aircraft’s flight path, particularly during descent. In this case, the first officer (pilot flying) relied upon automation to capture the assigned altitude and diverted his attention outside of the aircraft to assist the captain (pilot monitoring) in sighting the runway. As a result, neither pilot was monitoring the aircraft’s flight instruments or descent path as it approached and subsequently descended through the assigned level, which was also the minimum safe altitude.

The flight had been significantly delayed from its scheduled time of operation. The flight crew were aware of the reduced time margin for their scheduled return flight to depart Essendon prior to the 2300 curfew. In addition, neither pilot had operated at night into Essendon Airport, and the captain’s requested option of conducting an ILS approach to runway 26 had been declined by ATC due to traffic. The captain’s subsequent difficulty in identifying runway 35 at night, the delayed arrival of the aircraft at Essendon and the proximity of the curfew time probably contributed to the first officer (pilot flying) focussing his attention outside the aircraft at a critical time of flight.

Both flight crew had the previous days off duty and had a reasonable amount of sleep the night before. Although both flight crew had been awake for 1516 hours at the time of the occurrence, there was insufficient evidence to conclude that they were operating at a level of fatigue known to influence performance at the time of the occurrence. Nevertheless, they would probably have been operating at an elevated risk of fatigue during the subsequent two flights.

Findings

These findings should not be read as apportioning blame or liability to any particular organisation or individual.

• During radar vectoring to runway 35 at Essendon, the aircraft descended through the radar lowest safe altitude (2,100 ft). The extent to which there was a problem with the functioning of the aircraft’s automatic flight control system could not be determined.
• Due to the captain (pilot monitoring) having difficulty sighting the runway, as well as perceived pressure to complete the flight, the first officer (pilot flying) focussed his attention outside the aircraft at a critical time during the descent.
• The flight crew did not detect that the aircraft had descended through the assigned level (2,100 ft) until the aircraft reached 1,600 ft.

Safety action

Whether or not the ATSB identifies safety issues in the course of an investigation, relevant organisations may proactively initiate safety action in order to reduce their safety risk. The ATSB has been advised of the following proactive safety actions in response to this occurrence.

Aircraft operator

As a result of this occurrence, JetGo advised the ATSB that they had taken the following safety actions:

• The flight crew involved in the incident were subsequently provided with ground and simulator training for operations into Essendon at night.

Safety message

Flight crew should be mindful that during higher workload phases of flight, such as during approach and landing at an unfamiliar airport, introducing tasks that divert both flight crew members’ attention from monitoring the aircraft’s flight profile and altitude should be minimised. Further, during a visual approach, pilots must ensure that at least one pilot monitors the aircraft’s flight path profile and energy state.

The ATSB SafetyWatch highlights the broad concerns that come out of our investigation findings and from the occurrence data reported to us by industry.

An increasing trend has been identified where pilots do not effectively manage their aircraft’s flightpath when unexpected events arise during the approach to land.

When compared to other phases of flight, the approach and landing has a substantially increased workload and is traditionally the phase of flight associated with the highest accident rate. Flight crews must continuously monitor aircraft and approach parameters, and the external environment, to ensure they maintain a stable approach profile and make appropriate decisions for a safe landing.

The selection of inappropriate autoflight modes, unexpected developments, or any confusion about roles or procedures can contribute to decisions and actions that increase the safety risk to the aircraft and its passengers.

The ATSB SafetyWatch information on Descending too low on approach provides more resources and information.

About this report Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, a limited-scope, fact-gathering investigation was conducted in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions. Publishing information  Released in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 2018 Ownership of intellectual property rights in this publication Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia. Creative Commons licence With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence. Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work. The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.

__________

1. Eastern Daylight-saving Time (EDT): Coordinated Universal Time (UTC) + 11 hours. EDT was the time zone relevant where the occurrence took place and it has been used throughout the report to minimise confusion. The time in Brisbane was Eastern Standard Time, or UTC + 10 hours.
2. Pilot Flying (PF) and Pilot Monitoring (PM): procedurally assigned roles with specifically assigned duties at specific stages of a flight. The PF does most of the flying, except in defined circumstances; such as planning for descent, approach and landing. The PM carries out support duties and monitors the PF’s actions and the aircraft’s flight path.
3. Instrument Landing System: A landing aid which provides lateral and vertical guidance to flight crew during approach to land.
4. Radar vectoring: ATC provision of track bearings and altitudes used to guide and position an aircraft.
5. System-detected non-conformance alert that checks the conformance of the actual flight level of a surveillance track with respect to the cleared flight level inputted by the controller.