What happened

At 1253 Central Standard Time on 27 February 2014, a Boeing Company 737-8FE, registered VH-VOM (VOM), was radar vectored when outside controlled airspace, near Darwin, Northern Territory. Radar vectoring outside controlled airspace was not permitted, and may have brought VOM into conflict with aircraft that were unknown to air traffic control.

What the ATSB found

The ATSB found that weather in the Darwin area resulted in the majority of inbound aircraft diverting around storm cells. These diversions increased workload for the Approach East controller. The increased workload resulted in the controller using non-standard phraseology and not cancelling radar vectors prior to VOM leaving controlled airspace. Additionally, the flight crew of VOM had not reported ‘clear of weather’ as expected by the controller. This resulted in a lack of shared understanding between the flight crew and the controller.

What's been done as a result

Following this occurrence the Department of Defence introduced theoretical and simulator-based training to assist air traffic controllers to resolve unusual situations using clear communication and direction. The training reinforces positive and assertive control measures, skills that are especially necessary in high workload situations.

Safety message

This occurrence highlights that effective communication is essential for a shared understanding between flight crew and air traffic controllers. On this occasion, the use of non-standard phraseology by both parties resulted in different expectations and delay. Additionally, coordination between controllers is an essential component of their duties; however, this is not transmitted via radio. As a result, silence on an air traffic control frequency should not be interpreted by flight crew as an indicator of low workload for the controller.

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• Department of Defence
• aircraft operator
• air traffic controllers involved in the incident
• flight crew of VH-VOM.

References

Harris, D 2011, Human Performance on the Flight Deck, Ashgate, Surrey, England.

Kantowitz, BH and Casper, PA 1988, Human Workload in Aviation. In EL Wiener and DC Nagal (Eds) Human Factors in Aviation (pp. 157–187), Academic Press Limited, London, England.

Submissions

Under Part 4, Division 2 (Investigation Reports), Section 26 of the Transport Safety Investigation Act 2003 (the Act), the ATSB may provide a draft report, on a confidential basis, to any person whom the ATSB considers appropriate. Section 26 (1) (a) of the Act 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 involved air traffic controllers, the flight crew and operator of VH-VOM, the Department of Defence, Airservices Australia and the Civil Aviation Safety Authority.

Submissions were received from the flight crew and operator of VH-VOM, the Department of Defence and Airservices Australia. The submissions were reviewed and, where considered appropriate, the text of the draft report was amended accordingly.

Context

Personnel information

The flight crew on VH-VOM (VOM) were appropriately licenced and held current medical certificates. A review of their recent sleep and work patterns identified no fatiguerelated issues associated with the occurrence flight.

Darwin Approach was staffed by three Department of Defence (Defence) air traffic controllers, the:

• Supervisor
• Approach West controller
• Approach East controller.

Each controller was correctly endorsed and a review of their recent sleep and work patterns did not identify any fatiguerelated issues. The Approach supervisor was also endorsed in both Approach East and West.

The Approach East controller was working part-time, predominately in an administrative role. The controller worked on-console sufficiently frequently to maintain the Defence controller recency requirements.

Airspace information

Defence was the controlling authority for the Class C airspace^[6] within 40 NM (74 km) of Darwin Airport and below Flight Level (FL)^[7] 180. Airservices Australia (Airservices) had jurisdiction for the adjacent airspace and both agencies liaised extensively to provide an air traffic service in the area. Defence controllers use the same control techniques as Airservices when controlling civil, or a combination of civil and military, aircraft.

Procedures in place at Darwin required the airspace to be split between Approach East and Approach West during periods of higher traffic levels. Splitting the airspace resulted in fewer aircraft on a controller’s frequency, but could increase the need for coordination between those controllers. The procedures also required a supervisor be present when the airspace was split, to assist the controllers with coordination and sequencing.

The lowest levels of the controlled airspace to the east of Darwin that were controlled by the Darwin Approach East controller were:

• ground level from the airport to about 5 NM (9 km), then
• 1,000 ft from 5 NM to 15 NM (28 km)
• 2,500 ft from 15 NM to 30 NM (56 km)
• 6,500 ft from 30 NM to 40 NM (74 km).

The next controlled airspace step, with a lowest level of 8,500 ft out to 50 NM (93 km), was under the jurisdiction of Airservices.

The airspace below the steps was classified as Class G. Aircraft are, in certain circumstances, permitted to operate in Class G airspace without radio communication equipment or a transponder. Accordingly, there are limitations in the effectiveness of flight information services and surveillance information services in that airspace.

Meteorological information

The wet season in the far north of the Northern Territory extends from about October to April. This is also when most of the region’s hazardous aviation weather occurs. The wet season is characterised by cloudy conditions, lengthy periods of heavy rain, occasional thunderstorms and fresh to strong squally winds. During that period, aircraft regularly request track changes to avoid storm cells.

Controller responsibilities

Air traffic controllers are responsible for providing an air traffic service within the airspace under their jurisdiction. Such a service includes issuing clearances and information to prevent collision between aircraft and expediting and maintaining an orderly flow of traffic to and from the airport. The specific responsibilities of the Approach East and the Approach West controllers were dependent on the runway configuration in use at Darwin. When runway 29 was in use, the:

• Approach East controller was responsible for:
• arriving aircraft within the eastern portion of Darwin’s airspace
• sequencing aircraft arriving from the western portion of Darwin’s airspace
• separating arriving aircraft within the eastern portion of Darwin’s airspace with departing aircraft entering that airspace.
• Approach West controller was responsible for:
• aircraft in the western portion of Darwin’s airspace
• separating departing aircraft within the western portion of Darwin’s airspace with arriving aircraft entering that airspace
• issuing departing aircraft that will enter the eastern portion of Darwin’s airspace a separation-assured heading without prior coordination.

Further, procedures in place at Darwin stipulated that aircraft departing Darwin were to remain on the Approach West frequency as much as practicable.

The Approach East controller liaised with the Approach West and the Tower controllers to ensure the landing sequence was understood. Coordination was also required with the Airservices controllers responsible for the adjoining airspace.

The Approach Supervisor was responsible for, among other duties:

• supervising and coordinating the work of the Approach controllers
• planning traffic flow
• maintaining a constant liaison with the Tower supervisor regarding relevant weather information.

The Approach Supervisor who was responsible for monitoring controller workload on the day of the occurrence advised that they were aware that workload was high for the Approach East controller. They further stated that the traffic levels had built up quickly and, in response, they had taken on some of the controller’s tasks, predominately coordination with other agencies and sequencing.

Radar vectoring

The provision of navigational guidance to an aircraft in the form of specific headings, based on the use of an air traffic surveillance system, is known as radar vectoring. However, unless an emergency situation existed, aircraft were not to be radar vectored in Class G airspace.

One reason a controller can vector an arriving aircraft is to establish an orderly landing sequence at the airport. When an aircraft is vectored by a controller, the responsibility for navigation and terrain clearance is transferred to the controller.

When issuing an initial vector, the controller should advise the flight crew of:

• the reason for the vector, unless that reason was obvious
• the extent of the vector in general terms
• a tracking expectation at the completion of the vector.

On completion of vectoring, specific phraseology is to be used by the controller to transfer responsibility for navigation and terrain clearance back to flight crew. This phraseology includes advice to the aircrew of the aircraft’s position.

When aircraft leave controlled airspace, the controller is responsible for providing advice on other aircraft in the area. The other aircraft may either be observed, or known to be, in potential conflict with the aircraft leaving controlled airspace. The controller would be aware of aircraft in Class G airspace that had contacted them, or that were visible on their surveillance radar display. An additional source of information would be to liaise with the controller responsible for the provision of a flight information service (FIS) or a surveillance information service (SIS) in that area.

Flight crew responsibilities

Flight crew hold responsibility for the safe operation of their aircraft. On occasion, air traffic control assume responsibility for some aspects of flight, for example terrain clearance and navigation (see the section titled Controller responsibilities).

When a clearance is been requested by flight crew to deviate around weather, flight crew should advise air traffic control when the weather diversion is no longer required. This is done using the phrase ‘clear of weather’. Where circumstances warrant, and no documented phraseology is deemed appropriate, flight crew should use clear and concise plain language to indicate their intentions.

Similar occurrences

A review of the ATSB database did not identify any similar occurrences.

__________

6. Class C airspace: Controlled airspace surrounding major airports. All aircraft require an air traffic control clearance for operations in this airspace.
7. At altitudes above 10,000 ft in Australia, an aircraft’s height above mean sea level is referred to as a flight level (FL). FL 180 equates to 18,000 ft.

The occurrence

On 27 February 2014, a Boeing Company 737-8FE (737), registered VH-VOM (VOM), was being operated on a regular public transport flight from Sydney, New South Wales, to Darwin, Northern Territory. The arrival of the aircraft at Darwin coincided with the presence of a number of thunderstorms in the area (Figure 1).

In order to reduce the workload of the Approach controller associated with diverting arriving and departing aircraft around the storm cells, the air traffic control (ATC) approach unit responsible for the airspace within 40 NM (74 km) of the airport had split the airspace in to two control sectors. The division of airspace occurred along a line north-south through Darwin Airport, and each area (designated East and West) was under the control of separate Approach controllers operating on different radio frequencies.

Figure 1: Darwin weather radar picture at 1236 Central Standard Time^[1] showing rainfall associated with thunderstorm cells. The approximate location of VOM at that time is indicated by an arrow showing direction of travel. The range rings are at 50 km (27 NM) and 100 km (54 NM)

When the Approach East controller commenced their shift at 1230, the handover included details of four arriving aircraft in their airspace, and three arriving aircraft in the airspace under the jurisdiction of the Approach West controller. The majority of aircraft were not on their flightplanned track as they were diverting around storm cells. In addition to the arrivals, a number of aircraft departed Darwin during the development of this occurrence, including:

• Two aircraft heading to the south-east, through the airspace under the jurisdiction of the Approach East controller. These aircraft were tracking to air routes that were laterally separated from the tracks of aircraft inbound from that general direction.
• One aircraft that tracked to the north then returned to Darwin. This aircraft was instructed by the Approach East controller to hold overhead a visual point to the north of the airport for sequencing.
• Two aircraft heading to the north-east. One tracked low level and well clear of arriving traffic. The other tracked through the arrival track of an aircraft under the jurisdiction of the Approach East controller, requiring the controller to maintain a vertical standard between the two.

As a result of the traffic level, the workload for both controllers was relatively high.

At 1246, the Approach East controller advised the Tower controller of the landing sequence for runway 29. The sequence included six aircraft, with VOM fifth in the sequence. One other aircraft was also sequenced for runway 36, which crosses runway 29.

The weather on the day of the incident was typical for the Northern Australian wet season (see the section titled Meteorological information). The flight crews of the majority of aircraft in the Darwin area had been given approval by ATC to track around the storm cells. The crew of VOM intended to track for Howard Springs and then conduct an instrument landing system (ILS)^[2] approach for runway 29 (Figure 2). Additionally, the flight crew of VOM had been approved to operate up to 5 NM (9 km) either side of their intended track to avoid the storms.

Figure 2: Darwin weather radar picture at 1246 showing the approximate location of VOM while avoiding storm cells

The aircraft sequenced to land ahead of VOM on the ILS was considerably slower than VOM. To ensure separation between the aircraft on final for runway 29, at 1247 and with the aircraft 16 NM (30 km) south-east of Howard Springs, the Approach East controller cancelled the approach procedure issued to the flight crew of VOM and radar vectored (see the section titled Controller responsibilities) the aircraft right on to a heading of 360°. When the crew of VOM were issued with the radar vector, the preceding slower aircraft was 3 NM (6 km) east of Howard Springs and 14 NM (26 km) north-west of VOM, with a ground speed of 120 kt. At that time, VOM was indicating a ground speed of 260 kt.

The controller later reported that their intention had been for VOM to remain on the vector for only a short period of time. However, prior to cancelling the vector and clearing the aircraft direct to Howard Springs, at 1248 the flight crew of VOM requested a right turn heading 050° to avoid storm cells. The controller approved the diversion, instructing the flight crew to turn right on to a heading of 050° and asked them to report when they were ‘clear of weather’. In response, they advised the controller that ‘…we’re sitting in a big hole at the moment but there is weather out to the north of us and down to the south...’. The flight crew did not specifically advise the controller that the aircraft was clear of the storm cell.

Two minutes later, the flight crew of VOM requested to turn further right onto a heading of 100° to avoid weather. In response, the controller vectored the aircraft onto that heading. As VOM was heading away from Darwin, the controller changed the landing order of the aircraft arriving at Darwin. The aircraft that was to land after VOM was then resequenced ahead. Additionally, as VOM was tracking towards the edge of controlled airspace, 30 NM (56 km) east of Darwin, the Approach East controller advised the flight crew that their current track would shortly take the aircraft outside controlled airspace. When the controller asked the crew to advise their intentions, they stated that ‘… we’d like to come further right to join the ILS…’, but again did not report clear of weather.

Airservices Australia (Airservices) is responsible for providing the flight information service (FIS)^[3] and, workload permitting, the surveillance information service (SIS)^[4] in the Class G airspace^[5] adjacent to Darwin’s controlled airspace. At about this time, the Darwin Approach Supervisor advised the Airservices controller who was responsible for those services that VOM was about to leave controlled airspace to the east. The Airservices controller responded that there was no known traffic outside controlled airspace.

At 1252, VOM left 5,500 ft on descent to 4,000 ft as the aircraft left controlled airspace east of Darwin, heading 100°. At that time, the Approach East controller did not advise the flight crew of the aircraft’s position and any known traffic in the area. Additionally, the crew were not advised that they were required to resume their own navigation (see the section titled Controller responsibilities).

Twenty seconds later, when VOM was about 31 NM (57 km) east of Darwin, the flight crew requested a right turn to head 180°. The controller initially issued the radar vector, but, realising that the aircraft was outside controlled airspace, immediately cancelled the radar heading. Shortly after, the flight crew resumed their own navigation and tracked south.

The flight crew later reported that, due to the extent of the storms, the aircraft would not have been clear of weather and able to manoeuvre unrestricted until about 30 to 35 NM (56 to 65 km) east of Darwin.

The flight crew then requested to climb the aircraft into controlled airspace; however, this was not available due to an aircraft in that area at 7,000 ft tracking towards Darwin. At 1254, and with the aircraft 36 NM (67 km) east of Darwin, the flight crew of VOM were issued a clearance to track direct to Howard Springs. VOM re-entered controlled airspace at 1255 and subsequently landed at Darwin Airport via runway 29 at 1309.

__________

1. Central Standard Time (CST) was Coordinated Universal Time (UTC) + 9.5 hours.
2. A standard ground aid to landing, comprising two directional radio transmitters: the localizer, which provides direction in the horizontal plane; and the glideslope, for vertical plane direction, usually at an inclination of 3°. Distance measuring equipment or marker beacons along the approach provide distance information.
3. Flight information service (FIS): A service provided for the purpose of giving advice and information useful for the safe and efficient conduct of flights.
4. Surveillance information service (SIS): An on-request service provided to assist pilots of visual flight rules flights, within air traffic service surveillance system coverage in Class E and Class  G airspace, to avoid other aircraft or to assist in navigation.
5. Class G airspace: Uncontrolled airspace where aircraft operate without a clearance.

Safety analysis

Introduction

Thunderstorms in the Darwin area resulted in the majority of inbound aircraft tracking around storm cells, increasing the workload for the flight crews and the air traffic controllers. The flight crew of VH-VOM (VOM) had requested heading changes to avoid the weather that resulted in the aircraft tracking away from Darwin Airport. Ultimately, the aircraft exited controlled airspace without the required cancellation of radar vectoring. The controller subsequently issued a radar vector to the flight crew of VOM while the aircraft was outside controlled airspace. The following analysis will examine the various factors that led to this occurrence.

Controller workload

While the number of aircraft on the Approach East frequency was not high, the majority were diverting around storm cells. These diversions increased the controller’s workload as the arrival sequence became more complex and required increased levels of coordination. The situation was also exacerbated by a number of aircraft holding in the area.

The Approach East controller reported that their workload was higher than normal and that they were approaching their limit. As workload increased, the controller reported that they were spending additional time checking what they were doing, thus introducing a delay in communicating with flight crew. The supervising controller had recognised the controller’s workload and was assisting primarily with coordination and sequencing.

High workload is associated with an increase in error rate, and can also adversely affect an individual’s response to error (Harris, 2011 and Kantowitz & Casper, 1988). Time spent by a controller monitoring, but not communicating with, traffic was higher when dealing with ‘peak levels of air traffic’. This suggests that monitoring the traffic created a higher cognitive load than would be expected (Kantowitz & Casper, 1988).

In this occurrence, it is likely that the high level of workload resulted in increased monitoring. This added to the level of workload for the Approach East controller and reducing their ability to plan. As VOM approached the airspace boundary, standard phraseology was not used to advise the aircrew of their position and to transfer responsibility for navigation and terrain clearance back to the flight crew. This was likely due to the higher cognitive load being experienced by the controller.

The flight crew subsequently requested a heading change ‘due weather’, despite the aircraft being outside of controlled airspace. This was the third such request from that crew and, combined with the already high workload, the controller inadvertently responded by issuing a radar vector.

Additionally, on two separate occasions, the Approach East controller started, but did not complete, transmissions to the flight crew of VOM. These clipped transmissions were, more than likely, unfinished due to workload associated with completing coordination with other controllers. That workload prevented the controller from seeking clarification on possible headings that would have been acceptable to the flight crew.

Flight crew expectation

Due to aircraft in the airspace controlled by the Approach East and Approach West controllers being on different frequencies, the flight crew of VOM were not aware of all of the traffic in the Darwin airspace. Additionally, the flight crew were unaware of the higher than normal level of coordination being undertaken at the time, as this was not transmitted over the radio. As a result, the flight crew had no way on knowing the full extent of the controller’s workload.

When the flight crew of VOM acknowledged the Approach East controller’s advice that the aircraft would be going outside controlled airspace on the crew-requested heading, the crew should have been advised by the controller:

• of the aircraft’s position
• to resume their own navigation
• of any known traffic in the area.

In the absence of this information, the flight crew may not have understood the full implications of continuing on the crew-requested heading into uncontrolled airspace. That the flight crew requested another radar heading while outside controlled airspace supports this possibility.

The flight crew later reported that, following their request for vectors due weather, they expected that the aircraft would be vectored to commence the instrument landing system approach.

Controller expectation

When issuing the radar vectors to the flight crew of VOM to avoid the storms, and in accordance with documented requirements, the controller advised them to report clear of the weather. While the crew did respond to the controller advising of the surrounding weather, the controller was waiting for specific phraseology prior to facilitating the aircraft’s approach to Darwin Airport. Without that report, the controller believed that the flight crew were actively involved in avoiding storm cells.

Further reinforcing the controller’s belief was the flight crew’s acceptance to leave controlled airspace on the heading that the crew had requested in order to avoid weather. If the flight crew had advised an acceptable heading or how much longer the current heading was required, that may have assisted the Approach East controller to vector the aircraft for the instrument landing system approach. That represented a missed opportunity for common understanding.

Controller proficiency

Conditions that exacerbate error rate under high workload include inexperience with a task (Harris, 2011). Though the Approach East controller was correctly endorsed, their primary duty was administrative. To maintain endorsement recency, a controller was required to perform air traffic duties for a minimum number of hours over a stipulated time period.

While the controller met the recency requirements, given they were conducting part-time duties as a controller, their exposure to the Approach environment was ad hoc. This exposure, compounded by the onset of the wet season, may have resulted in a higher error rate compared to colleagues that were more routinely exposed to busy traffic sequences.

At the time of this occurrence, the Department of Defence was developing a number of simulator packages to enable Darwin air traffic controllers to gain experience in unusual operations. These packages, which were introduced in 2015, also help controllers maintain their skills during the dry season in readiness for the increased workload and complexity often seen during the wet season.

Findings

From the evidence available, the following findings are made with respect to the airspace event involving Boeing 737, registered VH-VOM, near Darwin, Northern Territory on 27 February 2014. These findings should not be read as apportioning blame or liability to any particular organisation or individual.

Contributing factors

• The non-standard phraseology used by the Approach East controller, just prior to VH-VOM going outside controlled airspace, did not emphasise that responsibility for navigation, terrain clearance and separation from other aircraft was being transferred to the flight crew.
• Despite the flight crew of VH-VOM providing an indication of the weather in the area, they did not comply with the requirement to specifically report ‘clear of weather’.
• A lack of a shared understanding between the flight crew of VH-VOM and the Approach East controller as to what was required from the other before the aircraft would be re-cleared to Darwin, delayed resolution and resulted in the aircraft exiting controlled airspace under radar vectors.
• While the Approach East controller met the Department of Defence recency requirements, working part-time in an administrative position limited their exposure to the tasks associated with controlling busy traffic sequences in adverse weather.
• A combination of the controller's recent and overall experience, traffic levels and the significant weather in the Darwin area, significantly increased their workload.
• The combination of the high workload and the previously issued vectors while VH-VOM was inside controlled airspace led to the controller inappropriately issuing a radar vector to an aircraft outside controlled airspace. This increased the risk of bringing VH-VOM into conflict with aircraft that were unknown to air traffic control.

Purpose of safety investigations & publishing information

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 2016 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.

On 12 March 2014, at about 1211 Central Standard Time, the crew of a United States military Boeing 737 aircraft, call sign ‘Convoy 7186’, requested a clearance from the air traffic control (ATC) planner at Darwin Airport, Northern Territory, for a flight to Kadena Air Base, Japan via the ‘A461’ air route.

The planner cleared Convoy 7186 to track to the destination via the ‘OCTOB’ waypoint at 5,000 ft above mean sea level (AMSL) and for an ‘OCTOB TWO’ standard instrument departure (SID).

At about 1245, the tower controller cleared the pilot of a Cessna 206 aircraft, registered VH-RAP (RAP), for take-off from runway 29 at Darwin, then to turn right onto a heading of 320° and climb to 3,000 ft AMSL.

The crew of Convoy 7186 then contacted the tower approaching the holding point for runway 29 and requested an ‘IFR release’. The tower controller asked the crew to repeat the call. The crew stated that they wanted to verify they were ‘direct OCTOB on the go, up to 5,000’. The tower controller replied ‘Affirm’.

At about 1248, the approach controller identified RAP and requested the pilot to maintain 2,000 ft to guarantee separation assurance with the following aircraft. Shortly after, the crew of Convoy 7186 contacted the approach controller and advised they were passing 2,000 ft on climb to 5,000 ft and tracking direct to OCTOB.

The approach controller immediately issued a safety alert and advised the crew that there was a VFR aircraft at 2,000 ft about 1 NM ahead and that Convoy 7186 was cleared on an OCTOB TWO departure. The crew replied, ‘Negative, it’s direct to OCTOB on the go’ and advised that they had the VFR aircraft in sight.

This incident highlights the importance of using standard phraseology in all radio communications.

Aviation Short Investigations Bulletin - Issue 32

On 7 March 2014, at about 1100 Western Standard Time, a Fairchild SA227DC, registered VH-ANW, with a crew of two and 18 passengers departed Truscott-Mungalalu aerodrome and was on climb passing through FL 125 when the cabin altitude annunciator illuminated.

The pressurisation system was checked by the crew and the cabin altitude was observed to be climbing at around a 1,000 feet per minute. While the flight crew were fitting (donning) their oxygen masks the CARGO DOOR warning light also illuminated. They then completed the checklist items which included turning off the engine air bleeds.

As part of the depressurisation drill the first officer made a passenger announcement (PA) requiring all passengers to don oxygen masks. This PA could not be heard by any of the passengers in the cabin. After approximately 5 minutes, a passenger seated in the front of the cabin noted that the crew had donned their masks so went forward to ask if the passengers needed to do the same.  This message was then passed throughout the cabin.

As the aircraft was above the maximum landing weight for a return to Truscott, the crew made the decision to continue on to Darwin and, due to the lower cruise altitude required when unpressurised, deviations from the track were necessary in order to avoid any significant weather.

The crew reported that after an uneventful landing in Darwin and engine shutdown, they debriefed the passengers.

They also reported that there were no issues experienced when closing the door at Truscott and that prior to engine start an additional confirmation check was made that the cargo door warning lights were extinguished. It was noted however, that there had been issues with that door in the previous weeks, including being hard to lock and a loss of cabin pressure.

Maintenance examination of the aircraft found that several of the ten locking pins on the cargo door were worn. As a precaution, seven of these pins were replaced. The pilot’s oxygen mask microphone was tested as serviceable and the first officer’s microphone was found to be faulty and was also replaced.

The operator has introduced amendments to the aircraft type PA and safety procedures checklists in order to confirm safety related PA announcements to passengers in these low capacity aircraft are understood and complied with.

The incident highlights the need, in lower capacity passenger aircraft without flight attendants, to assist in the cabin to confirm compliance with safety related announcements for the flight crew to confirm that the passengers have understood and complied with any safety message.

Aviation Short Investigations Bulletin - Issue 30

On 21 December 2013, at about 1230 Eastern Standard Time, a Cessna U206G aircraft, registered VH-UFT, departed Weipa for a charter flight to Hicks Island aeroplane landing area (ALA), Queensland. On board were the pilot and five passengers.

There was scattered cloud at different levels, showers of rain and a strong south-easterly wind. The pilot elected to cruise at about 1,500 ft above mean sea level (AMSL) until within 20 to 25 NM of Hicks Island, when the pilot descended the aircraft to remain clear of cloud.

After descending to about 500 ft above ground level (AGL), when about 20 NM from Hicks Island, the pilot was unable to continue the approach and remain in visual meteorological conditions (VMC) and attempted two more approaches. After unsuccessful attempts at reaching Hicks Island, the pilot elected to hold for about 40 minutes. After that time, the weather had not improved and the aircraft diverted to Lockhart River aerodrome.

After about 45 minutes on the ground, the pilot was advised that the weather at Haggerstone Island had improved and there were still showers in the area. At about 1520, the aircraft departed Lockhart River for Hicks Island, and about 30 minutes later, the pilot conducted an approach to runway 09. On final approach, at about 200 ft AGL, the aircraft encountered windshear, resulting in some loss of height.

The pilot continued the approach and after the initial touchdown, the aircraft remained on the ground for about 3-4 m then became airborne and subsequently bounced. The nose landing gear then contacted the ground and detached from the aircraft. The aircraft came to a stop on the runway.

This incident is a reminder to pilots to be go-around ready.

Aviation Short Investigation Bulletin - Issue 27

The pilot of a Cessna 404 aircraft registered VH-VEC was conducting an aerial survey flight north-east of Mangalore Aerodrome, Victoria. The flight was under the instrument flight rules (IFR) and flown at about 1500 ft above ground level. It took the aircraft across the extended centreline of runway 36.

The pilot made all required CTAF broadcasts while operating in the area. At the same time VEC was conducting the survey, several aircraft were departing Mangalore for a series of different navigational exercises.

The pilot of VEC continually attempted to call the pilots in the departing aircraft, to establish their position and intentions. However, as per their training, the pilot’s did not respond until their aircraft was at least five hundred feet above the ground. Also, to due to misunderstanding of the pilot of VEC’s intentions did not respond to his radio calls, unless the request was directed at their particular aircraft.

When the solo student pilot of VH-UNW departed runway 36, he focussed on flying the aircraft rather than communicating, until it reached 500 feet above ground level. Then he lowered the aircraft nose to check for traffic and saw VEC in close proximity. He turned UNW to the right at the same time that the pilot of VEC initiated a climbing turn to the right.

One of the safety concerns from the ATSB SafetyWatch is Safety around non-controlled aerodromes.

Also important is to understand the issues associated with unalerted see-and-avoid, as detailed in the ATSB’s research report, Limitations of the See-and Avoid Principles.

Aviation Short Investigations Bulletin - Issue 30

On 26 November 2013, a SOCATA TB-10 aircraft registered VH-YTT, departed Parafield Airport, South Australia, for solo night circuits in visual meteorological conditions. After one hour of flying circuits the student pilot conducted a touch and go landing prior to a final full stop circuit. At about 200 feet above the ground (AGL) after take-off the student noticed a vibration with a loss of power from the engine. The student initiated a gradual turn to the right until the large dark area of Parafield airport could be seen. At about 2120, just passing over the airport fence the student broadcast on the CTAF that the engine had failed. The student could see the white lights of the duty runway 21R/03L and the green lights of Bravo taxiway. The aircraft was at about 50 feet AGL and with partial engine power navigated toward the duty runway. There were no other aircraft on final or landing on runway 21R. The engine power was cutting in and out as the aircraft touched down on runway 03L at about a 30 degree angle, the aircraft remained on the runway, rolled through and turned off onto taxiway B5 where the engine lost all power and the aircraft stopped on the taxiway. The student broadcast on the CTAF that the aircraft was clear of the runway. The student pilot was uninjured and the aircraft was not damaged.

The incident highlights the importance of the points made in the ATSB booklet Avoidable Accidents No. 3 - Managing partial power loss after take-off in single-engine aircraft publication. Which include:

• pre-flight decision making and planning for emergencies and abnormal situations for the particular aerodrome
• conducting a thorough pre-flight and engine ground run to reduce the risk of a partial power loss occurring
• taking positive action and maintaining aircraft control either when turning back to the aerodrome or conducting a forced landing until on the ground, while being aware of flare energy and aircraft stall speeds.

Aviation Short Investigations Bulletin - Issue 31

On 7 March 2014, a Fokker 100 aircraft, registered VH-FZO, departed Perth on a scheduled passenger flight to Argyle, Western Australia. On board was a captain designated as the pilot flying (PF), and a training captain, seated in the right seat, designated as the pilot monitoring (PM).

During the cruise, the aircraft pitched down and both thrust levers came back towards idle to maintain the selected speed during the descent. The rate of descent reached about 1,700 feet per minute and the aircraft descended about 300 ft. The PF then disconnected autopilot 1 and connected autopilot 2.

The aircraft continued to Argyle and the crew commenced descent to the aerodrome. When at about 1,000 ft above ground level (AGL) and about 3 NM from the runway threshold, the PF stated that the thrust levers were stuck. The PM then tried to move the thrust levers and confirmed they were stuck. The PM applied force with both hands on the thrust levers and they jerked forwards, resulting in about a quarter of the normal available thrust. The PM directed the PF to get the aircraft back onto the normal profile and the PF extended full flap. Just prior to touchdown, the PM extended the speed brake and when at about 10 ft AGL, he applied sufficient force to move the thrust levers to the idle position. Engineers found that an elevator servo and a thrust lever servo had failed.

This incident provides an excellent example of how an experienced crew faced with a novel and unanticipated threat, were able to modify their roles and work together to safely complete the flight.

Aviation Short Investigations Bulletin - Issue 33

At approximately 0800 hours Eastern Standard Time on the morning of 22 March 1968 the Bell 204B helicopter, VH-UTW, owned and operated by Helicopter Utilities Pty. Ltd., commenced transporting a party of twenty-six journalists, photographers and public relations personnel from West Sale Aerodrome in Victoria to Barracouta Platform. Three separate flights were required to transport the party which had assembled principally from Sydney, Melbourne and the Gippsland area of Victoria and was visiting the platform for inspection and photographic purposes. The last group arrived at the platform shortly after midday.

Barracouta Platform stands in approximately 150 feet of water and is positioned over a natural gas recovery drilling point at latitude 38 degrees 18 minutes south, longitude 147 degrees 11 minutes east. The platform is 36 miles east south-east of the West Sale Aerodrome and 13 miles off-shore. Barracouta Platform is jointly owned and controlled by Esso Exploration and Production Australia Inc., and Haematite Petroleum Pty. Ltd.

At approximately 1215 hours VH-UTW took off with a party of television cameramen aboard for a short local flight around the platform for photographic purposes. Approximately five minutes later an approach from the east to the Barracouta helipad was made for the purpose of landing. The helicopter made a normal approach which terminated in the hover position with the heels of the undercarriage pontoons approximately four feet above the helipad surface. From this position directional control was lost and, after making contact with the helipad on the pontoons, it slewed through an arc of approximately 160 degrees in a clockwise direction as viewed from above. The helicopter came to rest on the helipad with its tail fin slightly over-hanging the western edge of the pad (Refer to Appendix A). The undercarriage had distorted in such away as to allow the main rotor blades to make contact with the helipad surf ace during the rundown period and this induced a fragmentation of the extremities of these blades. 

During the period between the initial loss of directional control and the final stopping of the main rotor blades, serious injuries were caused to seven of the eleven members of the press party who were observing the landing of the helicopter from positions on the helipad and on it's access stairway. In respect of three persons the injuries proved to be fatal but none of the six occupants of the helicopter was injured.

Conclusions

The pilot made a normal approach for landing and, when the aircraft was hovering with approximately four feet of clearance above the centre of the helipad deck, a catastrophic tail fin structural failure suddenly occurred, and deprived the pilot of directional control. The helicopter descended quickly onto the helipad deck and slewed through approximately 160 degrees about a vertical axis. During and immediately subsequent to this circumstance the principal injuries to bystanders occurred as a result of them coming into contact with the rotors or with pieces separating from the main rotor as it came into contact with the helipad deck.

The cause of this accident was that, during the assembly of the tail rotor, the inadvertent omission or loss of a trunnion thrust washer was not detected.

What happened

On 3 March 2014, the flight crew of a Tiger Airways Australia Pty Ltd (Tigerair) Airbus A320 were preparing for a scheduled passenger service from Sydney, New South Wales to Perth, Western Australia. The flight crew had earlier completed uneventful sectors from Sydney to the Gold Coast, Queensland, and return. As part of that preparation, the flight crew reviewed the operational flight plan (OFP) for the sector. The OFP was produced by the operator’s Operations Control Centre. That OFP contained significant errors in the aircraft weights, and as a consequence the required fuel upload for the sector was also significantly in error. The aircraft captain chose to re-calculate the required fuel load using resources available on the flight deck. The resultant required fuel load calculated and uplifted by the captain did not include the operator's requirement to carry a '60-minute top-up' additional fuel, resulting in the fuel upload being below that required under the operator's operations manual. The aircraft’s flight computers, however, identified that the aircraft would arrive at its destination with more than the minimum inflight fuel requirements. During the subsequent flight, the flight crew regularly checked the fuel usage and expected arrival fuel at Perth. All company and regulatory inflight fuel requirements for the flight from Sydney to Perth were met, and the aircraft landed with fuel in excess of the required fuel reserves.

What the ATSB found

There were deficiencies within the processes and procedures used by the operator's Operations Control Centre that permitted incorrect plans to be produced and subsequently provided to flight crew. This increased the risk that, in the time pressured environment of pre-flight planning, flight crews could either overlook incorrect data and accept an incorrect flight plan, or err in the calculation of the required fuel upload. Further, the operator provided limited guidance and assistance for flight crews on the processes and procedures for correcting identified fuel planning errors. For the occurrence flight crew, this lack of guidance, as well as the remoteness of resources that could assist, resulted in the decision to determine a correct required fuel load calculation using only those resources available on the flight deck. Due to the short layover between sectors, which was further aggravated by curfew restrictions, this increased the risk of critical fuel planning considerations being overlooked.

Safety message

A correctly calculated flight plan not only provides assurance to both the captain and the operator that all operational factors likely to influence the flight have been considered and accounted for, it also forms an important inflight validation tool to allow crews to monitor and continually assess those decisions made at the pre-flight stage. Where variances are noted, timely alternative plans can be implemented to ensure that aircraft arrive at either the destination or an alternate aerodrome with required fuel reserves preserved.

The occurrence

On 3 March 2014, the flight crew of a Tigerair Airbus A320 were rostered to conduct three scheduled passenger services. The crew commenced duty at 1700 Australian Eastern Daylight-saving Time^[1] in Sydney, New South Wales. The sectors were:

• Sydney to the Gold Coast, Queensland, with a departure time of 1800
• Gold Coast to Sydney, with a departure time of 2000
• Sydney to Perth, Western Australia, with a departure time of 2155.

At the commencement of duty, the flight crew received two of the three operational flight plans (OFP) for the upcoming sectors. The third was obtained about 10 minutes later. It was not until during the pre-flight stage of the third sector that the flight crew identified gross errors in the OFP for the Sydney to Perth sector. These errors resulted in a significant error in the calculated fuel required for the Sydney to Perth sector. Due to time and resource availability constraints, the captain chose to re-calculate the required fuel load using resources available on the flight deck. The captain did not upload sufficient fuel to meet the operator’s flight fuel requirements. The flight proceeded to Perth uneventfully and landed with a fuel reserve greater than that required under the regulations.

The operational flight plan

The OFP contained essential information necessary for the conduct of the relevant flight. It also formed the basis for the air traffic services (ATS) flight plan, which was included within the OFP. The OFP was required to contain specific information concerning that flight, including:

• aircraft registration, type and variant
• air traffic services flight plan data, including flight identification, place and time of departure, route, and place and time of arrival
• aircraft weight data, including dry operating weight, number of passengers and payload weight, take-off weight and landing weight
• fuel calculations, including a breakdown of all specific fuel quantities as required by regulation and the operator’s operations manual (OM)
• route segments with waypoints, distances, time intervals and tracks, planned cruising speed, altitudes/flight levels, and expected wind velocity
• for all en-route waypoints, a section for recording the estimated time of arrival, actual time of arrival and fuel remaining at that waypoint.

The section of the OFP that detailed the aircraft weights and fuel calculation also included information on the effect that an increase in weight would have on fuel burned during flight.

For multi-sector trips, all OFPs were required to be delivered via email to the operating flight crew at least 90 minutes before the scheduled start of the first flight.^[2] Flight crews were required to check the OFP for correct fuel load, flight details, as well as a number of other essential flight planning components.

Operations control centre

Flight planning was performed by the operator’s Operations Control Centre (OCC), which was located in Melbourne. The OCC was ‘responsible for the safe, efficient and cost effective utilisation of aircraft and flight crews ensuring that regulatory compliance and company requirements are achieved’.^[3] In fulfilling these functions, operations controllers (OC) were responsible for various operational tasks, including flight planning and load control for each flight. With respect to flight planning, OCs produced a number of products that were necessary for the proper planning and conduct of flights, including the OFP. On completion of the OFP, the OC was required to email the OFP to the flight crew and submit the ATS flight plan to the relevant ATS authority.

The operator had a structured training program for OCs that led to the issue of a certificate of competency. Once qualified, OCs were then required to maintain competency through the periodic completion of a recurrent training program.

The operator’s fuel policy in the operations manual

Background

The Civil Aviation Regulations (1988) (CAR) rr. 233-234 required the aircraft captain and the operator to ensure that an aircraft has sufficient fuel supplies for the safe conduct of the flight. CAR r. 234 also enabled the publication of fuel guidelines, which were contained within Civil Aviation Advisory Publication (CAAP) 234-1 Guidelines for aircraft fuel requirements.

CAAP 234-1 included guidelines for calculating the fuel required for a flight, as well as specific inflight fuel requirements. A component of the required fuel calculation, as well as inflight fuel requirement, was the fixed fuel reserve (FFR). The FFR was an amount of fuel that would enable 30 minutes of holding at 1,500 ft above an aerodrome at standard atmospheric conditions.

For an aircraft operator, CAR rr. 215 and 220 required:

• the operator to provide an OM
• the operator’s staff to comply with the OM
• that the OM include specific instructions for the computation of fuel quantities for all routes.

The operator’s fuel policy was contained within the OM Part A. It covered a number of general topics, including the captain’s authority, the fuel calculation, fuel monitoring, and in-flight fuel monitoring.

Captain’s authority

This section of the OM contained an overarching policy concerning fuel. It included the following statement:

It is the Captain’s responsibility to ensure that sufficient fuel is carried to operate the aircraft safely and efficiently in accordance with Company policy and procedures. Adequate fuel to cover the requirements of the trip, Variable Reserve, alternate (when required), reserve, required holding and taxi must be loaded prior to departure. Captains will uplift the minimum fuel quantity listed on the authorised OFP to achieve the operational requirements…

Fuel calculation

The section titled ‘fuel calculation’ was the means by which the OM detailed the fuel necessary for a flight, thereby meeting the CAR requirement that sufficient fuel be carried. It reflected the guidelines contained in CAAP 234-1. This section contained the components for determining the fuel required for a flight, and included the following:

• taxi fuel
• expected fuel usage for the flight
• should an alternate be required, fuel to meet that alternate requirement
• a variable fuel reserve of 10 per cent of the expected fuel usage and any additional alternate fuel (up to a maximum of 1,000 kg)
• a fixed reserve amount of 30 minutes fuel
• holding fuel, if traffic or weather conditions required it.

In addition, the policy required that if the sum (in minutes) of fixed reserve fuel plus any alternate fuel or holding fuel was less than 60 minutes, then an amount of fuel to reach that time was to be loaded. This extra fuel was known as the ‘60-minute top-up’. If the flight was limited by take-off performance or landing weight, the 60-minute top-up fuel was not to be applied before off-loading payload.

The fuel calculation in an OFP contained information on the expected increase in fuel burn for the flight that would result from an increase in take-off weight. The operator’s fuel policy did not include any guidance on this information, such as:

• the limit to the accuracy of the information as take-off weight increases
• at what point any change in take-off weight becomes sufficient to require a new OFP to be produced.

Fuel monitoring

This section of the OM contained a number of before flight requirements, including that ‘[t]he fuel on board agrees with the figure on the OFP, load sheet and is sufficient for the proposed flight’.

Inflight fuel monitoring

This section of the OM contained specific inflight fuel requirements. This included that, at each check, the expected fuel remaining on touchdown at the destination exceeded any alternate fuel requirement, including alternate variable reserve, plus reserve fuel. Reserve fuel was not defined, however, this section also stated that ‘[i]t is a legal requirement to touch down with not less than 30 minutes fixed reserve fuel intact’.

The pre-flight planning and the first two sectors

The OC responsible for producing the three OFPs and associated documentation recalled that the OFPs were produced and ready for transmission via email before 1800. These emails were recorded as being sent at 1636.

The captain recalled arriving at the operator’s Sydney crewing office about 30 minutes early to commence flight preparation. On arrival, the OFPs for the first two sectors were available, but the third OFP for the Sydney to Perth sector was missing. The captain reported calling the OCC on two occasions to ascertain the whereabouts of the missing OFP. It was finally delivered, via email, 10 minutes after the scheduled sign-on time of 1700. The Captain stated that, due to the need to concentrate on the first sector, there was insufficient time to review the Sydney to Perth OFP. The intent was to review this OFP after completing the second, Gold Coast to Sydney, sector.

The crew departed Sydney for the Gold Coast on schedule. The Sydney to Gold Coast and return sectors were uneventful, with the aircraft arriving back into Sydney 15 minutes ahead of schedule, at 2105.

The Sydney to Perth sector

The incorrect OFP

On arrival back in Sydney the flight crew commenced preparations for the final sector to Perth. This commenced with a review of the sector’s OFP. It was at that point that the flight crew first noticed that this OFP contained significant errors. The number of passengers recorded on the OFP was zero, as was the aircraft’s payload. The OFP showed a trip fuel of 9,368 kg, and a required fuel load of 12,296 kg. Finally, the fuel calculation section of the OFP stated that the additional fuel burn per 1,000 kg increase in take-off weight was 140 kg.

The actual passenger number was 177, representing a payload weight of 13,949 kg, while there was also additional payload in cargo totalling another 1,175 kg. The consequence of the omitted weight was that the fuel required for the flight was based on an aircraft weight that was significantly less than the actual weight. As a result, the fuel calculation figures were significantly less than that required for the flight. The OFP error meant that the fuel load would need to be recalculated before commencing the flight.

The curfew restrictions

Sydney airport curfew restrictions required weekday departing flights to be airborne no later than 2300. Additionally, departures between 2245 and 2300, known as the ‘shoulder period’, were required to use the southerly runways. When a departure was near the shoulder period and weather conditions required a northerly runway, aircraft were to commence taxi with sufficient time to ensure that the take-off commenced no later than 2245.

The captain reported that a few weeks earlier, another company flight had been refused permission to take off during the curfew shoulder period and had returned to the terminal, with a full load of passengers. That return to the terminal had resulted in significant disruption to both the passengers and the company’s operation.

Recalculation of the required fuel

The captain reported that a number of considerations were critical in making the decision on whether to seek an updated OFP:

• As the new OFP would be emailed to the flight crew, access to a computer terminal was required to obtain a printed copy. Such facilities were only available in the Sydney terminal, which required a walk of about 10 minutes each way, and the time required for the OCC to deliver the new OFP was unknown.
• There were no operational support personnel at the terminal to assist the flight crew with the compilation of a new OFP. The personnel present were for passenger and loading services only.
• The airport weather information was reporting the wind as 020 degrees at 10 kt, requiring a departure to the north. Any delay obtaining a new printed OFP had the potential to infringe on the shoulder period.
• The actual passenger and cargo load was available to the flight crew through the load sheet data provided by the terminal staff. This load sheet data provided accurate aircraft weights.
• The aircraft’s Flight Management Guidance System (FMGS) had the functionality and capacity to calculate an accurate required fuel load when the aircraft weights and many other variables regarding the route and flight were loaded into the system.
• The weather at Perth and at suitable en-route diversion airports was fine.

The OFP included the contact phone number for the OC who produced it, however, the OC was not contacted by the flight crew after the OFP errors were identified. The captain also had access to the phone number of the Duty Pilot, whose role included providing assistance to flight crew. The captain stated that attempts were made to contact the Duty Pilot, but that these calls were not answered.

Having discussed the matter with the first officer, the captain elected to determine the fuel load requirements using resources available on the aircraft’s flight deck, in this case the FMGS, and proceed with the flight to Perth without seeking an updated OFP with a hard copy. The captain and first officer independently calculated a required fuel load, and from these calculations and subsequent discussions the captain decided to upload 13.6 t of fuel. The captain was satisfied that this amount of fuel sufficiently met variable and mandatory fixed reserve fuel requirements, and that a number of airports along the route provided suitable options should an in-flight diversion become necessary.

Records identified that refuelling was completed at 2132, with the final fuel load being 13,520 kg. The captain stated that the FMGS was, at that time, showing an arrival fuel at Perth of 2.4 t.

The flight

The aircraft commenced taxiing at 2158. Take-off commenced at 2210.

The flight crew reported that, during the flight, they independently monitored the amount of fuel on board and fuel usage, knowing that the original OFP had been in error. As part of the process of continually monitoring the remaining fuel on board the aircraft, the flight crew recorded the fuel remaining at the top of the climb from Sydney, and at a number of waypoints along the route. They then reconciled the fuel remaining against the figures on the OFP^[4] for each leg and monitored the FMGS calculated arrival fuel to ensure the flight met the regulatory requirements. The flight crew also reported carrying out point-of-no-return calculations to ensure that, when the aircraft reached the point where they would be committed to the destination, the weather reports and fuel amounts would be sufficient to allow a safe landing. The monitoring process used by the flight crew was in excess of the OM’s requirement for inflight fuel monitoring, which for a flight from Sydney to Perth required a fuel check about every hour.

The flight continued uneventfully and the aircraft landed in Perth with about 1.9 t of fuel remaining. The captain subsequently reported the OFP inaccuracy to the operator, and in particular the concern about the safety implications if OFP inaccuracies were undetected by flight crew.

The operator’s internal investigation and audits

Operator’s investigation into the occurrence

In an internal report on the occurrence, the operator found that the:

• flight crew had been issued with an incorrect OFP that did not have any passengers or cargo included in the aircraft’s weight
• flight crew elected to add additional fuel above the figure required by the incorrect OFP, however, the amount of fuel the aircraft departed with did not meet the operator’s departure fuel 60-minute top-up requirement
• the correct 30-minute FFR for the adjusted aircraft weight was 1,139 kg
• the OFP had been delivered to the crew later than the time required by the OCCPPM
• the aircraft landed with 1,914 kg of fuel, which was above that required under the regulations.

The report made a number of recommendations, including that:

• the operator reinforce to flight crews:
  • the need to exercise vigilance in checking OFP data
  • that the duty pilot was an added resource available to assist flight crews
  • the need to request a new OFP where gross error exists
• OCC personnel receive adequate training in preparation of OFP’s using the new flight planning system.

The report stated that the correct minimum fuel upload for the flight was 15,343 kg. It also identified a number of areas requiring further investigation, including any guidance provided to flight crew regarding allowable errors in the OFP. With respect to this, the report stated that an examination of company documentation indicated that there was no specific guidance provided on allowable payload variations, nor on when a re-issued OFP was required.

Operator’s pre-occurrence audit of the OCC

An internal audit of the OCC conducted in September 2013 stated that the ‘overall operation of the OCC was considered to be satisfactory’. Management and the OCC staff were stated to be experienced and competent, while the operators demonstrated good knowledge of their duties and responsibilities. The audit contained two findings of an administrative nature, neither of which had a relationship to the production of OFPs.

Operator’s post-occurrence audit of the OCC

The operator’s internal investigation spawned a further internal investigation into errors in OFP’s issued to flight crew, as well as a further audit of the OCC. The error investigation identified a further three reported occurrences during 2014 of OFP’s that contained errors similar to that encountered by the occurrence flight crew.

The audit, conducted in July 2014, included the following statement in the executive summary:

Given the continued use of the Geneva (Day of Operations planning) and Navtech (Flight Planning) systems into the near term, the main areas of risk are in process development and staff training. In particular, flight plan preparation is considered to be of medium risk.

This statement appeared to relate to a number of audit observations and comments. The observations stated that there was little automated integration between the numerous systems that were used by the OCC staff during the production of an OFP. This resulted in a high level of manual data entry with the consequent high likelihood of errors being encountered. The comments identified that data update processes within the systems could result in incorrect data being processed manually into flight plans. The auditor also commented that the work environment (high workload and numerous distractions) could adversely affect the OFP production process.

With respect to the automated integration of the OCC systems, the audit also stated that the OCC introduced a new flight planning software package about 7 months before the occurrence. This resulted in many of the previously automated processes used to complete an OFP either being discontinued or becoming unstable. Further, when errors occurred in the production of an OFP, there were no automated warnings to alert the OC to this condition, resulting in error detection being reliant on the vigilance of the individual. The OC who produced the OFPs for the subject three sectors had not completed a formal training program for the new software, but had been provided a few ad hoc hands-on training sessions with an OCC duty manager. The July 2014 internal audit also noted that the OCC’s daily output of OFPs had increased substantially over the previous few years.

The audit contained four findings, none of which related to the processes involved in producing an OFP. One finding, concerning staff training records and syllabus, indirectly related to the internal investigation report’s recommendation that OCC staff receive adequate training in the preparation of an OFP.

Flight planning functions post February 2015

Tigerair advised that, as a result of the completed acquisition of Tigerair by the Virgin Australia Group in February 2015, Virgin Australia has subsequently assumed responsibility for all Tigerair flight planning functions.

__________

1. Australian Eastern Daylight-saving Time (AEDT) was Coordinated Universal Time (UTC) + 11 hours.
2. Crews were required to sign on for duty 60 minutes before the start of the first flight.
3. Tigerair Operations Control Centre Policy and Procedures Manual (OCCPPM).
4. The OFP route segment fuel burn calculations were not correct due to the aircraft weight errors, and therefore were not representative of the actual fuel burn for each leg.

Findings

From the evidence available, the following findings are made with respect to the flight planning error involving Airbus A320 registered VH‑VNJ that occurred at Sydney airport, New South Wales, on 3 March 2014. These findings should not be read as apportioning blame or liability to any particular organisation or individual.

Contributing factors

• On identifying that the operational flight plan for the Sydney to Perth sector had been based on an incorrect aircraft weights, resulting in the fuel calculation and subsequent fuel plan being significantly in error, the aircraft captain chose to re-calculate the required fuel load using resources available on the flight deck. The required fuel load calculated and uplifted did not include the operator's requirement to carry a '60-minute top-up' additional fuel, resulting in the aircraft departing with a fuel load that was below that required under the company's operations manual.
• There were deficiencies within the processes and procedures used by the operator's Operational Control Centre that permitted incorrect operational flight plans to be produced and subsequently provided to flight crew.
• The operator provided limited guidance and assistance for flight crews on the processes and procedures for correcting identified fuel planning errors. For the occurrence flight crew, this lack of guidance, as well as the remoteness of resources that could assist, resulted in the decision to determine a correct required fuel load calculation using only those resources available on the flight deck.

Other findings

• All company and regulatory in-flight fuel requirements for the flight from Sydney to Perth were met, and the aircraft landed with fuel in excess of the required fuel reserves.

Safety analysis

Tiger Airways Australia Pty Ltd used an Operations Control Centre (OCC) to provided flight planning support for the flight crew of their regular public transport flights. Operations controllers (OC) were responsible for the production of flight planning and supporting documentation, which included generating the operational flight plan (OFP) and associated air traffic services flight plan.

There are various reasons for using an OCC for flight planning, including cost and duty time considerations. The use of an OCC system to produce flight planning products enables operators to reduce the flight crew’s flight planning task from gathering information and developing the flight plan, to one of reviewing prepared documentation and a finalised OFP. This has enabled operators to significantly reduce the time spent by flight crew in the flight preparation phase. Under regulation and the operator’s own policy and procedures, however, the aircraft captain was responsible for the proper planning and conduct of a flight.

The production of a correct OFP is essential for the safe completion of a flight. It ensures, amongst other things, that:

• the calculated fuel upload contains all required components
• the fuel upload is sufficient for the required flight given the conditions expected for that flight
• there is an accurate method of tracking inflight fuel usage
• the aircraft will arrive at the destination with sufficient fuel to ensure a safe landing.

Fuel requirements

In accordance with the Civil Aviation Regulations (1988) rr. 215 and 220, the relevant fuel requirements for the occurrence flight were contained within the operator’s operation manual (OM). The OM contained two distinct fuel requirements for a flight that were differentiated by temporal criteria:

• the flight planning fuel requirements, referred to in the OM as the ‘fuel calculation’
• the in-flight fuel requirements.

Pre-flight fuel requirement

The fuel calculation required the flight crew of the occurrence flight to upload the ‘60-minute top-up’ fuel as part of the flight planning fuel calculation. With respect to the occurrence flight, the OCC provided the flight crew with an OFP that contained gross errors in the aircraft's payload and resultant operating weights. This in turn led to a fuel calculation that was significantly in error. These errors were detected by the flight crew during pre-flight. As a result, the flight crew re-calculated the required fuel upload based on actual load data information using resources available on the flight deck, and in particular the aircraft's flight computer. The required fuel load calculated and uplifted by the aircraft captain did not include the operator's requirement to carry a '60-minute top-up' additional fuel, resulting in the aircraft’s uploaded fuel being below that required under the operator's OM.

Inflight fuel requirement

While the aircraft did not meet the flight planning fuel upload requirement, all company and regulatory in-flight fuel requirements were met for the flight from Sydney to Perth. The flight crew monitored the fuel usage during the Sydney to Perth sector in accordance with, and most likely in excess of, the OM inflight fuel monitoring requirements. This, and the actual arrival fuel being in excess of the regulatory and OM required minimum fuel reserves, indicate that the aircraft met the inflight fuel requirements for the Perth to Sydney sector.

The 60-minute top-up requirement

There were a number of factors about the top-up requirement that are relevant:

• This additional fuel represented a more conservative approach to fuel safety than that contained in the guidance material provided by the Civil Aviation Advisory Publication 234-1.
• The top-up fuel component was not a component of the inflight fuel requirement.
• The safety basis of the top-up requirement can be diminished due to the operator’s policy of offloading this fuel component instead of payload when aircraft operating limitations became an issue.

OCC deficiencies

The inaccurate OFP was the result of deficiencies within the processes and procedures used by the operator's OCC. While the operator’s 2013 internal audit of the OCC did not identify any deficiencies in processes or procedures, particularly along the lines of those exposed by this occurrence, the subsequent investigations initiated as a result of the occurrence and the 2014 audit identified a number of relevant deficiencies.

The 2014 audit identified an increased risk to the production of an OFP due to process issues and training of OCC staff. Specifically related to this occurrence were the audit’s comments and observations identifying that there were no system defences able to detect errors introduced through manual data entry or automated updating before the OFP was transmitted to flight crew. Therefore, the principal defence in identifying any errors was the vigilance of the flight crew. This increased the risk that, in a time pressured environment of pre-flight planning, flight crews could either overlook incorrect data and accept an incorrect OFP, or as occurred in this occurrence, identify the error and be required to calculate the fuel upload requirement themselves. However, on this occasion and the other three occasions identified in the internal investigation, the flight crew did discover the error.

Guidance on OFP errors

Correcting the occurrence flight’s OFP error was further complicated by the limited guidance and assistance that the operator provided to correct errors in fuel calculation. While the OFP contained information with respect to increased fuel burn for every one tonne increase in take-off weight, there was no guidance on the limits to which this information could be used, nor at what point gross error in the take-off weight required a new OFP to be produced. For the occurrence flight crew, this lack of guidance, as well as the remoteness of resources that could assist, influenced the decision to determine a correct required fuel load calculation using only those resources available on the flight deck. Due to the short layover between sectors, which was in turn further aggravated by curfew restrictions, this increased the risk of critical fuel planning considerations being overlooked.

Sources and submissions

Sources of information

The sources of information during the investigation included the:

• The captain of VH-VNJ
• Tiger Airways Australia Pty Ltd
• The Civil Aviation Safety Authority

Submissions

Under Part 4, Division 2 (Investigation Reports), Section 26 of the Transport Safety Investigation Act 2003 (the Act), the Australian Transport Safety Bureau (ATSB) may provide a draft report, on a confidential basis, to any person whom the ATSB considers appropriate. Section 26 (1) (a) of the Act 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 Civil Aviation Safety Authority, the crew of VH-VNJ and Tiger Airways Australia Pty Ltd.

Submissions were received from the aircraft captain, Tiger Airways Australia Pty Ltd, and the Civil Aviation Safety Authority. The submissions were reviewed and where considered appropriate, the text of the report was amended accordingly.

Purpose of safety investigations & publishing information

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 2017 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.

During the evening on 15 February 2014, and Airbus A320, registered VH-VNQ, was preparing to depart Hobart, Tasmania, for a flight to Melbourne, Victoria. The crew completed pre-departure activities including entry of take-off reference speeds and the flex temperature (for a flex temperature take-off) into the aircraft’s Flight Management Guidance System (FMGS). The crew started engines and taxied for runway 12, but thunderstorms in the area delayed departure.

After holding for about 75 minutes, waiting for the weather to clear, the crew entered runway 12 and backtracked to the threshold. As they backtracked, the crew were able to gain a better appreciation of the weather in the direction of departure, and assessed their departure options. The crew entered their planned departure procedure into the FMGS, but noticed that the navigation display called for a right turn after take-off, contrary to the published procedure which called for a left turn.

The crew attempted to clear the departure anomaly by changing the departure runway to the reciprocal runway, then re-selecting the correct runway. This action failed to clear the anomaly, so the crew elected to continue with the departure and use heading mode to command a left turn at the appropriate time, rather than allow the auto-flight system to guide the aircraft into a right turn. The crew was unaware at the time, but by changing the departure runway in an attempt to clear the anomaly, take-off reference speeds and the flex temperature previously entered into the FMGS, were removed.

As the flex temperature take-off commenced, the crew noticed that flight mode annunciations were not as they would normally appear. An electronic centralised aircraft monitoring system caution then alerted the crew that the thrust levers were not correctly set, and the crew noticed that the take-off reference speeds were not displayed on the primary flight display airspeed indicators. The captain elected to continue the take-off and advanced the thrust levers to the take-off/go around setting, commanding maximum available thrust. The captain also restored previously entered take-off data by pressing the appropriate line select key on one of the multi-purpose control and display units. As the take-of continued, auto-flight modes became active and the crew selected heading mode to manually command a left turn as planned. The flight to Melbourne then proceeded uneventfully.

The operator’s investigation into the incident identified issues relating to the consistency of their before take-off checklist with that published by the aircraft manufacturer, and the status of the FMGS software installed in the flight simulators used by the operator. In response to the incident, the operator implemented a number of initiatives, including alignment of the before take-off checklist with that published by the aircraft manufacturer, implementation of a revised crew briefing format, provision of relevant educational material to flight crew and implementation of a flight simulator software upgrade.

For operators, this incident highlights the need for robust checklists and checklist management procedures that effectively cater for a wide range of operational scenarios, the importance of ensuring that the performance of training equipment accurately reflects the performance of operational equipment, and the importance of consistently accurate FMGS aeronautical data. For flight crew, this incident serves to highlight the importance of careful attention to FMGS aeronautical data and highlights the need for extra caution following an interruption to the normal sequence of events during preparation for departure. The incident also reinforces the importance of Airbus ‘Golden Rules for Pilots’, particularly the first rule: Fly, navigate and communicate (in this order and with appropriate task sharing).

Aviation Short Investigations Bulletin - Issue 37