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Flight below minimum altitude involving Cessna Citation 510, VH-IEQ, 13 km west of Bankstown Airport, New South Wales, 16 November 2022

Final report

Executive summary

What happened

On 16 November 2022, a non-scheduled passenger transport flight was conducted in a Cessna Citation Mustang, registered VH-IEQ, between Young Airport and Bankstown Airport, New South Wales. On board were a pilot and one passenger. 

As the aircraft approached Bankstown Airport to land under the instrument flight rules, about 10 minutes after last light, the pilot established contact with air traffic control (ATC), where a ‘visual’ approach was requested. ATC approved the pilot to fly directly toward final approach for runway 11 centre. Immediately after this clearance, the pilot started tracking toward final approach for this runway and descended to a height of 1,000 ft, which was about 800 ft below the lowest safe altitude for the area. ATC subsequently issued a terrain safety alert. An uneventful landing was conducted at 2020 local time.

What the ATSB found

The ATSB found that the pilot had submitted a flight plan earlier in the day for an arrival after last light, when more stringent rules applied than day operations. However, the pilot followed the rules applicable to day operations as there was still some ambient light available to allow features on the ground to be visually identified and avoided. This resulted in the pilot descending below the lowest safe altitude applicable for operations at night.

Safety message

This incident highlights the importance of planning, particularly around times when rules change, such as the transition from day to night. In this case, the pilot reported that flying a published instrument approach procedure, rather than declaring ‘visual’ would have been a more suitable plan for this flight.

The investigation

Decisions regarding the scope of an investigation are based on many factors, including the level of safety benefit likely to be obtained from an investigation and the associated resources required. For this occurrence, a limited-scope investigation was conducted in order to produce a short investigation report, and allow for greater industry awareness of findings that affect safety and potential learning opportunities.

The occurrence

In the late afternoon of 16 November 2022, a non-scheduled passenger transport flight was conducted in a Cessna Citation Mustang, registered VH-IEQ (IEQ) between Young Airport and Bankstown Airport, New South Wales (Figure 1). On board were a pilot and one passenger. 

This was the fourth and final flight of the day, with the pilot completing 3 earlier flights in the aircraft. National Airspace Information Planning System records indicated that the pilot submitted all flight plans for these flights at about 0448 local time, with this plan showing a planned departure from Young at about 1945 for the incident flight. This flight was planned to follow flight routes under the instrument flight rules (IFR)[1] and arrive at Bankstown at about 2014.

Figure 1: Flight path of VH-IEQ and incident location

Figure 1: Flight path of VH-IEQ and incident location

Image showing flight path of aircraft (red line) on a map, with take-off, arrival and location of flight below lowest safe altitude.

Source: Google Earth and Geoscience Australia, annotated by the ATSB

Flight data recorded by the GPS navigation unit onboard the aircraft indicated that a take-off was commenced from Young on runway 19 at about 1946. After take-off, the aircraft started tracking to the east and climbed to a cruising altitude of flight level (FL)[2] 230 by about 1956.

At about 2001, the aircraft started to descend, continuing to track toward IFR waypoint WATLE. During this descent, at about 2004, last light[3] for Bankstown occurred. Six minutes later, the aircraft arrived overhead WATLE and proceeded to follow the planned IFR route denoted ‘Y20’, directly toward Bankstown Airport, 28 NM (52 km) to the east. At 2014:48, at waypoint NOLEM (Figure 2), the aircraft levelled out at 2,000 ft[4] above mean sea level and continued to track toward Bankstown. At this time, the pilot established first contact with Bankstown Tower air traffic control (ATC) near waypoint NOLEM (Figure 2), with the following communication exchange:

2014:48 IEQ: ‘Bankstown tower IEQ is 11 miles west 2,000 with Quebec visual inbound’

2014:59 BANKSTOWN TOWER: ‘IEQ BK TWR Join Final Runway 11 centre’

2015:08 IEQ: ‘Join Final 11 centre IEQ’

Immediately after responding to ATC, flight data indicated that the aircraft began a left turn onto a track of approximately 060° (true). Near the completion of the left turn, at 2015:22, the aircraft began to descend from 2,000 ft (labelled ‘left turn toward final approach and start of descent below 2,000 feet’ in Figure 2). The aircraft continued to descend on this track, levelling out at 1,000 ft at 2016:20. Around this time, ATC identified that the aircraft was ‘too low’, and issued a ‘Terrain’ safety alert at the location marked in Figure 2. The communication exchange for the safety alert between ATC and the pilot were as follows:

2016:30 BANKSTOWN TOWER: ‘IEQ Safety Alert Terrain QNH[5] is 1012’

2016:38 IEQ: ‘Roger copy 1012 IEQ I'm ahh visual’

2016:43 BANKSTOWN TOWER: ‘IEQ’

At the time the safety alert was issued and while maintaining at 1,000 ft, flight track data showed that the aircraft started to change track to the right by 15° to 075° for about 2 NM (3.7 km). The aircraft then changed track again to the right toward the intersection of the Bankstown Airport control zone and the extended centreline of runway 11 centre. Just prior to entering the control zone at 2017:55, Bankstown Tower provided the aircraft with a clearance to land, which was acknowledged by the pilot. At this time, the aircraft turned toward runway 11 centre and started to descend from 1,000 ft. An uneventful landing on runway 11 centre was conducted at 2019:56.

Figure 2: Flight path of VH-IEQ showing descent to 1,000 ft and approach to land

Figure 2: Flight path of VH-IEQ showing descent to 1,000 ft and approach to land

Note: Image showing flight path of aircraft (red line) on a low level enroute chart (right) and from the perspective of the approach from the NOLEM waypoint (left).

Source: Google Earth and Airservices Australia, annotated by the ATSB

Context

Meteorological information

The meteorological report (METAR)[6] for Bankstown Airport released at 2000 local time indicated the following weather conditions for the aircraft’s arrival:

  • winds at 6 kt from the north-west
  • visibility greater than 10 km
  • 3 layers of cloud, comprising scattered[7] at 5,100 ft and at 7,000 ft, and broken at 8,200 ft above the ground
  • the QNH was 1012 hPA.

Images from weather cameras at the time of the incident located at Camden and Sydney Airports facing the direction of the aircraft and Bankstown Airport are shown in Figure 3. The images show that less than half of the sky is covered by cloud, with the cloud tops illuminated by the sun. There were no weather cameras operating at Bankstown Airport.

The Bureau of Meteorology advised that these weather cameras were configured 'to work in low light and will use the light available to provide the best image’, that is, the images shown in Figure 3 ‘look brighter than the actual conditions experienced by the pilot’. However, relatively clear atmospheric conditions are shown by the images, with well-defined silhouettes of ground‑based features.

Figure 3: Images from weather cameras at Camden and Sydney Airports

Figure 3: Images from weather cameras at Camden and Sydney Airports

Source: Bureau of Meteorology, annotated by the ATSB

Visual approach to Bankstown Airport

During the approach, the pilot advised ATC that they were ‘visual’. This transmission signified that the requirements for a visual approach under the IFR could be met. ATC responded providing an instruction to ‘join final 11 centre’, which constituted a clearance to enter the Bankstown control zone on the centre line of runway 11 centre, tracking toward that runway.

As last light was at 2004 and this instruction was provided at 2014, this meant that the visual approach requirements for IFR flights by night applied. 

To assist with conducting the visual approach, runway 11 centre was equipped with a precision approach path indicator system.[8]

Required actions by pilot following instructions from ATC

AIP ENR 1.1 paragraph 2.2.7.2[9] (Operations in Class D Airspace)[10] stated that in circumstances where ATC responds with the aircraft callsign and instructions, the pilot must comply with ATC instructions. It also states that ‘when no level instruction is issued’, the pilot may ‘descend as necessary to join the aerodrome traffic circuit’. In this case, ATC had instructed the pilot to join final runway 11 centre without a level instruction. The instructions meant that the pilot was required to fly the aircraft to enter the Bankstown control zone on the extended centreline for runway 11 centre. However, minimum height requirements applied to the flight as discussed in the next section.

Minimum height requirements during a visual approach for an IFR flight at night

During a visual approach at night, subparagraph 91.305(3)(b)(i) of the Civil Aviation Safety Regulations 1998 (CASR 91.305(3)(b)(i)) allowed an IFR flight to descend below minimum stipulated heights if the aircraft was being flown in accordance with:

…requirements relating to visual approach or departure procedures published in the authorised aeronautical information for the flight.

AIP ENR 1.5 section 1.14 articulated these requirements. AIP ENR 1.5 paragraph 1.14.6(b)[11] was relevant to this flight and included the provision that the pilot may visually approach the aerodrome by night when at an altitude not below the lowest safe altitude (LSALT)[12] or minimum sector altitude (MSA)[13] for the route segment, if the aircraft was established:

(1) clear of cloud;

(2) in sight of ground or water;

(3) with a flight visibility not less than 5,000M; and

(4) subsequently can maintain (1), (2) and (3) at an altitude not less than:

…

(ii) one of the following:

Route segment LSALT/MSA; or…

Based on the reported weather conditions, clauses 1, 2 and 3 noted above were achieved when the request for a visual approach was made by the pilot to ATC. Further, the AIP stipulated one of the conditions allowing an aircraft to descend below LSALT was when the aircraft was:

Within 5NM (7NM for a runway equipped with an ILS/GLS) of the aerodrome, aligned with the runway centreline and established not below “on slope” on the T-VASIS or PAPI; 

Based on the ATC clearance provided to the pilot, and runway 11 centre being equipped with a PAPI, this meant that the aircraft could descend below LSALT once aligned with the runway centreline and not below on-slope of the PAPI and within 5 NM (9.3 km) of the PAPI.

Calculation of the lowest safe altitude

Flight data showed that after the initial climb from Young Airport, the aircraft had been above the published LSALT for the duration of the flight until reaching waypoint NOLEM.

AIP GEN 3.3 section 4 defined how to calculate the LSALT. Specifically, paragraph 4.2 stated:

For routes and route segments not shown on AIP aeronautical charts, the lowest safe altitude must not be less than that calculated in accordance with para 4.3 within an area defined in the following paras 4.6, 4.7, 4.8 and 4.9.

For this flight, paragraph 4.3 clause 4.3(a) stated the LSALT was to be calculated using the following method:

Where the highest obstacle is more than 360FT above the height determined for terrain, the LSALT must be 1,000FT above the highest obstacle; …

Additionally, paragraph 4.5 stated:

If the navigation of the aircraft is inaccurate, or the aircraft is deliberately flown off-track, or where there is a failure of any radio navigation aid normally available, the area to be considered is a circle centred on the DR position, with a radius of 5NM plus 20% of the air distance flown from the last positive fix.

Paragraph 4.5 applied to the incident flight after the pilot intentionally flew off-track toward final approach for runway 11 centre with the last positive fix being the waypoint NOLEM. Based on this, the ATSB calculated the LSALT for the aircraft between NOLEM and being aligned with runway 11 centre. An extract of the visual terminal chart applicable to the area is shown in Figure 4. 

The aircraft was equipped with an approved global navigation satellite system, which was being used for navigation under RNP 2[14] meaning that the aircraft remained with a positive fix for the duration of the flight. For RNP 2 operations, AIP GEN 3.3 paragraph 4.7 required the following area to be considered for LSALT calculations:

…within an area of 5NM [9.3km] surround and including the departure point, the destination and each side of the nominal track.

This area is shown for the incident between the red circle labelled ‘Lowest safe altitude area at turn’ and the magenta circle labelled ‘Lowest safe altitude area from final intercept’ in Figure 4. Calculations were also performed in the circumstance where the aircraft flew to an extended 5 NM final for runway 11 centre, the earliest point of descent when using the PAPI, and this is depicted by the green circle labelled ‘Lowest safe altitude area from 5 NM final’ in Figure 4.

Figure 4 also shows 2 charted obstacles in the area. This indicated that paragraph 4.3(a) from AIP GEN 3.3 applied to this part of the flight. The highest obstacle in the area to be considered for LSALT was the tower ‘TWO RN’ at 870 ft above mean sea level, located about 2.5 NM (4.6 km) to the right of track, as labelled in Figure 4. Another tower was present about 2.5 NM (4.6 km) to the left of track at a height of 813 ft. Based on this, the LSALT for the aircraft during this segment of the flight was 1,870 ft.

Figure 4: Area applicable to lowest safe altitude calculations for VH-IEQ between flight path deviation and the extended centreline of runway 11 centre at Bankstown Airport

Figure 4: Area applicable to lowest safe altitude calculations for VH-IEQ between flight path deviation and the extended centreline of runway 11 centre at Bankstown Airport

Source: Airservices Australia, annotated by the ATSB

Lowest safe altitude for a visual approach during the day

AIP ENR 1.5 section 1.14 paragraph 1.14.6(b) stipulated the same requirements for a visual approach by an aeroplane in the day, except for clause (4)(ii), which required pilots to maintain an altitude not less than:

The minimum height prescribed by CASR 91.265 or 91.267 as relevant to the location of the aircraft.

For the location of this incident, regulation 91.265 for flights over ‘populous areas and public gatherings’ applied. This stipulated that the aeroplane must be flown more than 1,000 ft above the highest feature or obstacle within a horizontal radius of 600 m of the point on the ground or water immediately below the aeroplane. Based on this, the height flown by the aircraft was above that required for an IFR visual approach during the day.

Decision to descend below lowest safe altitude

During an interview with the ATSB, the pilot recalled the following observations about the navigation conditions during the approach:

  • It was a light evening with plenty of twilight allowing the ground to be seen clearly.
  • The light was sufficient to see a clear horizon.
  • Ground features were able to be clearly seen, sufficient to identify the aircraft’s precise position.
  • All known obstacles could be seen.

Based on these observations, the pilot reported deciding to ‘call visual’.

The pilot’s description of the weather conditions was consistent with those recorded by the Bureau of Meteorology. 

The pilot stated that, during a self-briefing prior to departure, the time of last light had been recorded for Young Airport and not Bankstown Airport as intended. The pilot also reported reviewing the last light time prior to descent to Bankstown Airport. Last light at Young Airport occurred about 12 minutes later than Bankstown Airport due to it being further west. The pilot later stated that recording the last light time for Young instead of Bankstown in the briefing sheet possibly contributed to the decision to descend and conduct the approach flown.

The pilot stated that descending to 1,000 ft assisted with meeting the stabilised approach criteria, which was:

“in a landing configuration with gear down, full flap, the sink rate … under 1,000 feet per minute and the checklists … completed…by 1,000 feet”. 

The pilot stated that a challenge with using the PAPI was not being able to descend until 5 NM (9.3 km) from the runway, and that this was up to 1,000 ft higher than the ideal glideslope of about 1,600 ft at that location if the minimum sector altitude of 2,500 ft was used. The pilot also stated:

“the aircraft will then give you a lot of warnings about sink rate and terrain which can be very stressful… for passengers”. 

For these reasons, the pilot stated:

“that is why I elected to descent to make sure that I was able to get that stabilised approach criteria. And …, it only worked because I had such good visibility in the twilight, I was able to see the ground, and I was able to see visually where I was.”

The pilot also stated that a motivation for declaring visual was to ‘fit in’ with the other traffic in the Bankstown area. However, the pilot stated that, on reflection, flying an instrument approach (specifically the RNP approach, rather than declaring visual) would have been a better solution for arriving close to or after last light for the aircraft stating:

“the only way to do it to achieve the stabilised approach is by the RNP”.

Fatigue considerations

The ATSB evaluated the likelihood that the pilot was fatigued at the time of the incident. Some areas of increased risk of fatigue potentially relevant related to:

  • continued period of wakefulness/length of duty period
  • split duty and efficacy of naps
  • quantity of sleep, particularly relating to early starts.

The pilot reported obtaining 7.5 hours of sleep immediately prior to the incident, and 8 hours for each of the 2 nights prior to that. The pilot submitted a flight plan at 0448 and was likely awake for some time prior to this. The pilot’s flight duty period (FDP) for the day started at 0630,[15] had a split duty rest period between 1030 and 1730 that included a 1-hour nap, and then was on duty again until 2100. As the incident occurred at 2016, the pilot’s total FDP was 14 hours and 30 minutes, which was 30 minutes over the maximum allowed under Appendix 4 of Civil Aviation Order 48.1 for single-pilot air transport operations, or to an approved fatigue risk management system. However, section 5.3 of Appendix 4 stated: 

Despite the FDP limits provided in the operations manual, in unforeseen operational circumstances at the discretion of the pilot in command, the FDP limits in the operations manual may be extended by up to 1 hour.

The pilot reported having a discussion with the chief pilot about extending the FDP limits due to floods in the area delaying the departure time for the flights. However, the final flight of the day arrived within 5 minutes of the planned time.

Based on the reported sleep obtained, the pilot was likely not fatigued at the time of the incident.

Safety analysis

After last light, the pilot contacted Bankstown Tower declaring that they were ‘visual’ at 2,000 ft. This signified to ATC that requirements for a visual approach at night under the IFR could be achieved. The controller’s subsequent instruction to join final runway 11 centre indicated that the pilot could track toward the extended centreline for that runway.

The clearance from ATC did not specify an altitude, allowing the pilot to descend to the LSALT until established within 5 NM (9.3 km) of the PAPI for runway 11 centre. However, immediately after this clearance, the pilot descended to 1,000 ft, below the LSALT of 1,870 ft. This LSALT applied due to the 2 towers in the area rising to a height of 870 ft about 2.5 NM (4.6 km) from the aircraft. Analysis by the ATSB showed that flight above the LSALT could have been achieved by maintaining altitude between the point of diversion until being aligned with the extended centreline of runway 11 centre within 5NM (9.3 km) of the PAPI.

The pilot reported that the actual approach flown was as they had planned and declared ‘visual’ as they could ‘see the obstacles’. Weather camera imagery showed that the conditions were consistent with the pilot’s description. However, the camera imagery was likely brighter than that experienced by the pilot from altitude looking down on the obstacles and terrain. In this case, the flight path flown by the pilot was applicable and suitable for operations in the day. However, both the planned and actual times when the flight below LSALT occurred were after last light, based on the elapsed time between first contact with ATC and landing. Further, the pilot also reported incorrectly recording a later time for last light than actual, based on Young instead of Bankstown. The additional perceived duration of usable light possibly contributed to the decision to conduct the approach flown. The pilot reported that, on reflection, a better option would have been to fly an instrument approach procedure when planning to arrive at Bankstown just prior to or after last light. This indicated that these requirements could have been considered prior to the flight and represented a missed opportunity during flight planning.

Findings

ATSB investigation report findings focus on safety factors (that is, events and conditions that increase risk). Safety factors include ‘contributing factors’ and ‘other factors that increased risk’ (that is, factors that did not meet the definition of a contributing factor for this occurrence but were still considered important to include in the report for the purpose of increasing awareness and enhancing safety). In addition ‘other findings’ may be included to provide important information about topics other than safety factors. 

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

From the evidence available, the following findings are made with respect to the flight below minimum altitude involving Cessna Citation 510, VH-IEQ, 13 km west of Bankstown Airport, New South Wales, on 16 November 2022. 

Contributing factors

  • While conducting a visual approach to Bankstown Airport, the aircraft descended 800 ft below the lowest safe altitude for operations at night, reducing the assurance for separation from terrain and ground-based obstacles.

Sources and submissions

Sources of information

The sources of information during the investigation included:

  • the pilot
  • Airservices Australia
  • recorded data from the GPS unit on the aircraft.

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
  • Navair Flight Operations Pty Ltd
  • the Civil Aviation Safety Authority
  • Airservices Australia.

Submissions were received from:

  • the pilot
  • 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

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 2024

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[1]     Instrument flight rules (IFR): a set of regulations that permit the pilot to operate an aircraft to operate in instrument meteorological conditions (IMC), which have much lower weather minimums than visual flight rules (VFR).

[2]     Flight level: 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 230 equates to 23,000 ft.

[3]     Last light is defined as the end of evening civil twilight, marking the commencement of night. The end of evening civil twilight occurs when the Sun’s centre is 6° below the horizon.

[4]     This was also the published lowest safe altitude between IFR waypoint NOLEM and Bankstown Airport.

[5]     QNH: the altimeter barometric pressure subscale setting used to indicate the height above mean seal level.

[6]     METAR: a routine aerodrome weather report issued at routine times, hourly or half-hourly.

[7]     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.

[8]     Precision Approach Path Indicator (PAPI): a ground-based system that uses a system of coloured lights used by pilots to identify the correct glide path to the runway when conducting a visual approach.

[9]     AIP ENR 1 GENERAL RULES AND PROCEDURES, section 1.1 GENERAL RULES, subsection 2 OPERATIONS IN CONTROLLED AIRSPACE, sub subsection 2.2 Air Traffic Control Clearances and Instructions

[10]    Class D: This is the controlled airspace that surrounds general aviation and regional airports equipped with a control tower. All flights require ATC clearance.

[11]    AIP ENR 1 General Rules and Procedures, section 1.14 Visual Approach Requirements for IFR flights, subsection 6, sub subsection 6(b) Visual approach by Night, dated 02 DEC 2021.

[12]    Lowest safe altitude (LSALT): The lowest altitude that provides safe terrain clearance at a given place.

[13]    Minimum sector altitude (MSA): The lowest altitude that will provide a minimum clearance of 1,000 ft above all objects located in an area contained within a circle or a sector of a circle of 25 NM (46 km) or 10 NM (19 km) radius centred on a significant point. 

[14]    Required navigation performance (RNP) levels refer to the performance required from the navigation system. RNP 2 is primarily used in continental airspace where there is some ground navigation aid infrastructure. 

[15]    A flight duty period starts when ‘a person is required by an AOC [Air Operator’s Certificate] holder to report for a duty period in which 1 or more flights as an FCM [flight crew member] are undertaken’. The flight plan submission at 0448 was therefore not counted as duty (only time awake).

Occurrence summary

Investigation number AO-2022-061
Occurrence date 16/11/2022
Location 15 km west of Bankstown Airport
State New South Wales
Report release date 05/06/2024
Report status Final
Investigation level Short
Investigation type Occurrence Investigation
Investigation status Completed
Mode of transport Aviation
Aviation occurrence category Flight below minimum altitude
Occurrence class Incident
Highest injury level None

Aircraft details

Manufacturer Textron Aviation Inc.
Model 510
Registration VH-IEQ
Serial number 510-0462
Aircraft operator NAVAIR FLIGHT OPERATIONS PTY LTD
Sector Jet
Operation type Part 135 Air transport operations - smaller aeroplanes
Departure point Young Aerodrome
Destination Bankstown Aerodrome
Damage Nil

Derailment of freight train 4PM9, at Inverleigh, Victoria, on 14 November 2022

Summary

On 10 November 2022, SCT Logistics freight train 4PM9 departed Perth, Western Australia for Melbourne, Victoria. At about 0450 on 14 November, the train was travelling at about 80 km/h when it passed over a culvert located to the east of the township of Inverleigh in Victoria. Soon after, there was a loss of brake pipe pressure, and the leading end of the train came to a stop across the Hamilton Highway level crossing. The embankment supporting the track at the location of the culvert had collapsed and 16 wagons had derailed. Ten of the original 55 wagons were still attached to the leading 5 locomotives. 

Victoria's Chief Investigator Transport Safety is conducting the investigation under the Transport Safety Investigation Act 2003 (Cth), under a collaboration agreement with the ATSB.

A preliminary report into the incident was published on the ATSB website on 06 February 2023.

The drafting of the final investigation report has been completed and is currently being internally reviewed.

Preliminary report

Preliminary report released 24 February 2023

This preliminary report details factual information established in the investigation’s early evidence collection phase and has been prepared to provide timely information to the industry and public. Preliminary reports contain no analysis or findings, which will be detailed in the investigation’s final report. The information contained in this preliminary report is released in accordance with section 25 of the Transport Safety Investigation Act 2003.

The occurrence

Passage of freight train 4PM9

On 10 November 2022, SCT Logistics freight train 4PM9 departed Perth, Western Australia for Melbourne, Victoria. The train left Adelaide, South Australia on 13 November and consisted of 5 locomotives hauling 55 wagons[1] and was about 1800 m in length. The train was operating on the Australian Rail Track Corporation (ARTC) standard gauge network.

The train arrived in Horsham, Victoria at about 2320[2] on 13 November. A crew change occurred in Horsham and the train resumed its trip to Melbourne that would take it through Ararat, Maroona and then Inverleigh (Figure 1).

Figure 1: Standard gauge route from Horsham to Melbourne

Figure 1: Standard gauge route from Horsham to Melbourne

Source: e-way   Electronic Street Directory   Version 2.2 (c) Copyright Melway Publishing Pty. Ltd. annotated by Chief Investigator, Transport Safety

At about 0450 on 14 November, train 4PM9 travelling at about 80 km/h passed over a culvert located to the east of the township of Inverleigh. Soon after, there was a loss of brake pipe pressure[3] and the leading end of the train came to a stop across the Hamilton Highway level crossing. Ten of the original 55 wagons were still attached to the leading 5 locomotives. The next 16 wagons were derailed including 7, 5-pack articulated wagons (Figure 2).

Figure 2: Aerial view of derailed train 4PM9

Figure 2: Aerial view of derailed train 4PM9

Source: Aerial footage provided by ABC News, annotated by CITS

The embankment supporting the track at the location of the culvert had collapsed (Figure 3).

Figure 3: The pipe culvert and the collapsed track formation

Figure 3: The pipe culvert and the collapsed track formation

Source: Chief Investigator, Transport Safety

Context

Location

The derailment occurred about 3 km east of the township of Inverleigh on a section of track located between the Hamilton Highway and the Barwon River (Figure 4). Travelling in an easterly direction, the track ran parallel to the Hamilton Highway before curving towards and across the highway. The derailment occurred within the Mid Barwon catchment area that made up part of the Barwon drainage basin. The agricultural land on either side of the rail reserve generally sloped from the highway down towards the Barwon River. Therefore, run-off from rainfall flowed from the north side of the track through culverts (below the track) towards the Barwon River.

Figure 4: Derailment site of train 4PM9

Figure 4: Derailment site of train 4PM9

Source: Google maps, annotated by the Chief Investigator, Transport Safety

Track infrastructure

The standard gauge track at Inverleigh was a single, bi-directional line, and consisted of 60 kg/m rail fastened to concrete sleepers. The track through the location was carried on an embankment that was at a height of about 3 m at the location of the wash-away (at the culvert). This culvert was located at the 96.805 track km mark[4] and comprised of a 750 mm diameter concrete pipe embedded at the base of the embankment carrying the track.

Rainfall

Heavy rain fell in Inverleigh from the late evening of 13 November and through the early hours of the morning of 14 November. A weather monitoring station at Gnarwarre[5], located about 12 km from Inverleigh recorded about 42 mm of rain in the 12-hour period[6] before the derailment, and local weather stations in Inverleigh recorded rainfall of around 70 mm.

Bureau of Meteorology (BoM) radar-derived[7] rainfall accumulations estimated that between 50 and 100 mm of rain fell at Inverleigh in the 24 hours to 0900 on 14 November 2022 (Figure 5).

Figure 5: Radar-derived rainfall accumulations

Figure 5: Radar-derived rainfall accumulations

Source: Bureau of Meteorology, annotated by Chief Investigator, Transport Safety

Further investigation

To date, CITS has:

  • attended and completed derailment site inspections
  • examined drainage in the waterway catchment area and commenced hydrology studies
  • examined train consist and operational information
  • interviewed the driver of train 4PM9
  • commenced collection of other relevant information

The investigation is continuing and will include review and examination of:

  • the train consist and operation of the train
  • the waterway catchment area, including local catchment features
  • the effect of prior rainfall on soil moisture and catchment flow
  • culvert design including capacity
  • track infrastructure including inspection and maintenance
  • weather warnings

Should a critical safety issue be identified during the course of the investigation, the ATSB will immediately notify relevant parties so appropriate and timely safety action can be taken.

A final report will be released at the conclusion of the investigation.

Australian Transport Safety Bureau

About the ATSB

The ATSB is an independent Commonwealth Government statutory agency. It is governed by a Commission and is entirely separate from transport regulators, policy makers and service providers.

The ATSB’s purpose is to improve the safety of, and public confidence in, aviation, rail and marine transport through:

  • independent investigation of transport accidents and other safety occurrences
  • safety data recording, analysis and research
  • fostering safety awareness, knowledge and action.

The ATSB is responsible for investigating accidents and other transport safety matters involving civil aviation, marine and rail operations in Australia, as well as participating in overseas investigations involving Australian-registered aircraft and ships. It prioritises investigations that have the potential to deliver the greatest public benefit through improvements to transport safety.

The ATSB performs its functions in accordance with the provisions of the Transport Safety Investigation Act 2003 and Regulations and, where applicable, international agreements.

Rail safety investigations in Victoria

Most transport safety investigations into rail accidents and incidents in Victoria and New South Wales (NSW) are conducted in accordance with the Collaboration Agreement for Rail Safety Investigations and Other Matters between the Commonwealth Government of Australia, the State Government of Victoria, and the State Government of New South Wales. Under the Collaboration Agreement, rail safety investigations are conducted and resourced in Victoria by the Chief Investigator, Transport Safety (CITS) and in New South Wales by the Office of Transport Safety Investigations (OTSI), on behalf of the ATSB, under the provisions of the Transport Safety Investigation Act 2003.

The Chief Investigator, Transport Safety (CITS) is a statutory position established in 2006 to conduct independent, no-blame investigation of transport safety matters in Victoria. CITS has a broad safety remit that includes the investigation of rail (including tram), marine and bus incidents.

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 on the ATSB website. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue.

[2]     Australian Eastern Daylight Time (AEDT).

[3]     A loss of brake pipe pressure is often associated with a loss of brake pipe integrity and is an indication of a train parting.

[4]     Rail km from Melbourne.

[5]     Managed by the Department of Environment, Land Water and Planning and named Barwon River@Pollocksford

[6]     From about 1700 on 13 November 2023.

[7]     The BoM rainfall accumulation images are made by blending measurements from rain gauges (accurate point data) and radar. Radar data is calibrated with rain gauge data and is used to fill in the "gaps" between rain gauges. 

Occurrence summary

Investigation number RO-2022-013
Occurrence date 14/11/2022
Location 3 km east of Inverleigh
State Victoria
Report release date 24/02/2023
Report status Preliminary
Anticipated completion Q2 2026
Investigation level Systemic
Investigation type Occurrence Investigation
Investigation phase Final report: Internal review
Investigation status Active
Mode of transport Rail
Rail occurrence category Derailment
Occurrence class Serious Incident
Highest injury level None

Train details

Train operator SCT Logistics
Train number 4PM9
Rail vehicle sector Freight
Departure point Perth, Western Australia
Destination Melbourne, Victoria
Train damage Substantial

Collision with terrain involving Robinson R44, VH-TKI, at Forresters Beach, New South Wales, on 19 November 2022

Final report

Report release date: 09/06/2023

Executive summary

What happened

On 19 November 2022, the pilot of a Robinson Helicopter Company R44, registered VH-TKI, was conducting a private flight from a nearby property to a function centre at Forresters Beach, New South Wales with 2 passengers onboard. The proposed landing site was the carpark of the venue. During the approach, the pilot reported an uncommanded yaw to the right which was unable to be recovered. Following a loss of control, the helicopter struck powerlines before colliding with terrain. The occupants received minor injuries and the helicopter sustained substantial damage.

What the ATSB found

The ATSB found that during approach to a confined area landing site, the helicopter experienced a loss of tail rotor effectiveness and accompanying right yaw. The pilot’s response was ineffective at recovering control, however, with the position of the aircraft on approach to the confined area it could not be established if the control of the aircraft could have been recovered before the helicopter collided with powerlines and terrain.

Safety message

Helicopter pilots should remain cognisant of the factors that may induce unanticipated yaw, especially the relative wind direction, and either avoid or manage their influence on the helicopter’s anti‑torque system by maintaining positive control of the yaw rate. If unanticipated yaw is encountered, prompt and correct pilot response is essential. Depending on the yaw rate recovery may not be immediate, but maintaining the recovery control inputs is the most effective way to stop the yaw.

A prompt response is especially important for confined area operations where the physical characteristics of the landing site may limit the options available to the pilot in the event of an unanticipated yaw or emergency landing.

The investigation

Decisions regarding the scope of an investigation are based on many factors, including the level of safety benefit likely to be obtained from an investigation and the associated resources required. For this occurrence, a limited-scope investigation was conducted in order to produce a short investigation report and allow for greater industry awareness of findings that affect safety and potential learning opportunities.

The occurrence

On 19 November 2022, the pilot of a Robinson Helicopter R44, registered VH-TKI, was conducting a private flight to take 2 passengers from a nearby property to a function centre at Forresters Beach, New South Wales (Figure 2).

At about 1800 local time, the pilot commenced the first of 2 approaches to the proposed landing site, located in the carpark of the function centre. The pilot reported that the approach was towards the north-east, with the wind coming from 10º to the left of the nose and that all indications were normal.

After experiencing instability in the hover over the landing area, the pilot elected to conduct a missed approach (see Video 1). During the second approach, as the helicopter slowed to an airspeed of approximately 20 kt and approached the tree line at approximately 100 ft above ground level, the pilot reported the helicopter began an uncommanded yaw to the right that could not be corrected with full left pedal input.

Recognising the helicopter’s proximity to the people gathered at the venue and in the street below, the pilot attempted to manoeuvre the helicopter away from the landing site towards a clearing on the opposite side of the road. However, the rate of rotation increased, with the helicopter making two and a half revolutions before striking powerlines and colliding with terrain. The pilot and both passengers sustained minor injuries and the helicopter was substantially damaged (Figure 1).

Figure 1: Accident site

Figure 1: Accident site

Source: ATSB

Context

Pilot information

The pilot held a valid commercial pilot license (helicopter) with a class 2 medical certificate.

At the time of the accident, the pilot had about 190 hours of aeronautical experience, with most of this experience in the R44. Since obtaining their license in 2016, they had accrued approximately 90 hours of flying. The pilot also completed a low-level rating in an R44 on 1 October 2022. This operational rating also counted as a flight review.

The low-level rating included low-level emergencies and autorotations,[1] however, unanticipated yaw, (see the section titled Unanticipated yaw) was not covered. The pilot did recall receiving classroom-based training in relation to the recognition of the onset of loss of tail rotor effectiveness (LTE) during their license training and recalled conducting loss of tail rotor emergency training as part of a previous flight review.

Helicopter information

The R44 is a 4-place helicopter that is primarily all metal construction with a 2-blade main and tail rotor system powered by a 6-cylinder Lycoming piston engine. VH-TKI was manufactured in the United States in 1994 and issued serial number 0040. It was registered in Australia in 2021. The helicopter was maintained in accordance with the manufacturer’s maintenance schedule, which required a periodic inspection every 100 hours or 12 months, whichever came first. The maintenance release indicated that VH-TKI had accumulated a total of 1,582.9 hours in service at the time of the occurrence.

The helicopter had flown 3.8 hours since the last periodic inspection, and no outstanding defects were noted in the maintenance release. The helicopter was within the weight-and-balance and centre-of-gravity limits. The co-pilot controls had been removed and were stored under the pilot’s seat for the flight.

Weather

The pilot advised that as part of their pre-flight planning, they had obtained the weather forecast and prior to departure continued to monitor the observations, at Williamtown Aerodrome, located about 75 km to the north-north-east of the landing site. Williamtown was the closest aerodrome on the coast with briefing and NOTAM[2] services available.

The weather forecast for Williamtown indicated the conditions expected for the planned time of arrival would be CAVOK[3] with winds from the north-east at 12 kt. Conditions throughout the flight were reportedly as forecast and provided smooth flying conditions.

The nearest Bureau of Meteorology weather observation site was located at Gosford, 10 km south-south-west of the landing site. Weather data recorded at about the time of the occurrence showed the wind from the north-east at 6–10 kt.

The ATSB received video footage of both approaches (see video 1 and 2) which showed the palm trees at the edge of the landing area moving in the wind. The pilot advised that flags positioned by the road at the front of the venue were used to ascertain the local wind direction. Eye-witness reports did not provide a clear indication of the wind speed, but confirmed the wind was coming from the north-east.

The approaches

The Robinson R44 Pilots Operating Handbook stated that in-ground effect hover controllability had been demonstrated to 17 kt wind from all directions. While a limiting figure was not provided for an out of ground effect[4] hover, the pilot advised that a power assurance check conducted prior to commencing the approach confirmed that out of ground effect power existed.

In the video footage of the first approach, (Video 1) taken from the edge of the landing site, the helicopter became unstable in the final stages of the approach, with the nose yawing to the right. The yaw was arrested by the pilot, but sideways drift was evident as the approach continued. Upon terminating into a hover over the landing site, the tail again began yawing from side to side before the pilot conducted a missed approach.

Video 1: First approach

Source: Witness

The data extracted from the onboard GPS (Figure 2), indicated the track for both approaches was approximately south‑east.

Figure 2: Final approach path

Figure 2: Final approach path

The flight track extracted from the helicopter GPS is shown in red. The inset shows the proximity of the obstacles (power lines and palm trees) under the approach to the planned landing area. The relative wind can be seen to be almost perpendicular to the track from the left, an area of known hazard for the onset of LTE.

Source: Google Earth with GPS data, annotated by ATSB

Video footage of the second approach (Video 2) showed that the helicopter approached at approximately 100 ft above ground level before suddenly yawing to the right. The rate of rotation could be seen to accelerate, and the radius of turn tighten as the helicopter rotated through two and a half revolutions. Directional control of the helicopter was not recovered, and the rotational speed of the main rotor blades could be heard to decrease as the helicopter began to descend. The rotating descent continued until the helicopter struck powerlines and then collided with terrain.

Video 2: Accident sequence

Source: Witness

 

Proposed landing site

The pilot had been in contact with the venue’s management and visited the location twice prior to the flight, to confirm the dimensions and the suitability of the carpark as the landing site. Civil Aviation Safety Regulations (CASR) 1998, 91.410 Use of aerodromes required that an aircraft take-off or land from

a place that is suitable... and the aircraft can land at, or take off from the place safely having regard to all the circumstances of the proposed landing or take-off (including the prevailing weather conditions)

The venue was located on a main road in a built-up suburban area (Figure 2). The approach to the carpark was planned to overfly a clearing on the opposite side of the road to the venue before passing over powerlines along the road, and palm trees at the perimeter of the carpark (Figure 3). The helicopter would be required to enter an out of ground effect hover at approximately 50 ft above ground level, before conducting a vertical descent to the ground.

CASA guidance in Advisory Circular AC 91-29 Guidelines for helicopters – suitable places to take off and land acknowledges that as a private operation, the safety margins that would otherwise be expected to be applied to performance calculations when conducting commercial operations do not apply.

There is no legal obligation on helicopter pilots operating solely under Part 91 to apply safety margins to the take-off or landing distance, take-off performance and obstacle avoidance ability which has been determined when using the helicopter manufacturer's data.

Additionally, AC 91-29 detailed when a particular landing site was considered to be a confined area and the obligations of the pilot when selecting the particular landing site.

An unprepared landing site that has obstructions that require a steeper than normal approach, where the manoeuvring space in the ground cushion is limited, or whenever obstructions force a steeper than normal climb-out angle is often defined as ‘Confined Area’. While a pilot can land at a Confined Area, they still have to apply all the basic principles.

While not having landed at this location before, the pilot had operated into other confined area landing sites on previous flights.

Figure 3: Planned landing site looking in the direction of the approach

Figure 3: Planned landing site looking in the direction of the approach

Source: ATSB

Where a site is considered to be a confined landing area, CASA guidance in Advisory Circular AC 91-29 Guidelines for helicopters – suitable places to take off and land recommended that in addition to aircraft performance, ‘the height velocity diagram should also be carefully considered before operating from these areas’. The R44 flight manual included a height-velocity diagram, which defined the conditions from which a safe power-off landing could be made. A notation on the diagram encouraged pilots to avoid operation in the shaded area. The approximate speed and height at which the aircraft was flown during the occurrence with respect to the height-velocity diagram is shown in Figure 4.

Figure 4: R44 height-velocity diagram

Figure 4: R44 height-velocity diagram

Source: Robinson Helicopter Co. R44 Piot operating handbook, annotated by ATSB

Unanticipated yaw

The FAA Helicopter Flying Handbook Chapter 11: Helicopter emergencies and hazards stated that loss of tail rotor effectiveness (LTE) is ‘an uncommanded rapid yaw towards the advancing blade’. It ‘is an aerodynamic condition and is the result of a control margin deficiency in the tail rotor’. Tail rotor thrust is affected by numerous factors, including relative wind, forward airspeed, power setting and main rotor blade airflow interfering with airflow through the tail rotor.

Several wind directions relative to the nose of the helicopter, shown in Figure 5, are conducive to LTE when single rotor helicopters fitted with counterclockwise rotating main rotor blades such as the R44, are flown at speeds of less than 30 kt. The wind directions that were of relevance during VH-TKI’s approach included the following:

  • 210–330°, tail rotor vortex ring state. Turbulent air produced by the tail rotor blade vortices recirculate through the tail rotor leading to the development of unsteady airflow through the tail rotor and fluctuations in tail rotor thrust. The change in thrust means that the airflow around the tail rotor will vary in direction and speed, requiring an increase in rudder pedal workload to maintain directional control. The loss of this tail rotor efficiency increases the power demand and there is an additional antitorque requirement.
  • 285–315°, main rotor disc vortex interference. Winds at velocities of 10–30 kt from the left front cause the main rotor blade vortices to enter the tail rotor disc producing turbulent airflow that interferes with the tail rotor. High power settings generate an associated increase in main rotor downwash and blade tip vortices. The turbulent airflow increases the likelihood of main rotor disc vortex interference as illustrated in Figure 5.

Figure 5: Azimuths[5] of concern for loss of tail rotor effectiveness

Figure 5: Azimuths[5] of concern for loss of tail rotor effectiveness

Source: FAA Helicopter Flying Handbook

The FAA advisory circular AC 90-95 – Unanticipated Right Yaw in Helicopters stated that

Any manoeuvre which requires the pilot to operate in a high-power, low-airspeed environment with a left crosswind or tailwind creates an environment where unanticipated right yaw may occur.

It also provides guidance on how to avoid the onset of LTE and advised pilots to avoid the following flight conditions when operating below 30 kt:

  • tailwinds
  • out of ground effect hovers and high-power demand situations such as downwind turns
  • hovering out of ground effect in winds of about 8–12 kt.

Robinson Helicopter Company safety notice SN-42: Unanticipated yaw

The Robinson Helicopter Company advised that to avoid unanticipated yaw, pilots should be aware of conditions that may require large or rapid pedal inputs. They recommend practising slow, steady-rate hovering pedal turns to maintain proficiency in controlling yaw.

Recovery from unanticipated yaw

In addition to providing guidance on how to avoid the sudden onset of unanticipated yaw, AC 90‑95 provided the following recovery technique:

  • apply full left pedal while simultaneously moving cyclic[6] control forward to increase speed.
  • if altitude permits, reduce power.
  • as recovery is affected, adjust controls for normal forward flight.

The pilot stated that the yaw to the right was uncommanded and unexpected. As the rotation began, the pilot applied full left anti-torque pedal input to arrest the rotation and manoeuvred towards a clearing on the opposite side of the road. While maintaining left pedal input, they also applied forward cyclic to increase the helicopter’s forward speed. These inputs were consistent with the recovery guidance for unanticipated yaw.

The pilot further advised that they probably raised the collective in an attempt to fly away. As the collective is raised, there is a simultaneous and equal increase in pitch angle of all main rotor blades. An increase in pitch angle also results in increased drag on the main rotor blades. To counter this adverse effect, the R44 has a throttle correlator mechanism attached to the collective control that increases the throttle when the collective is raised.

A condition known as overpitching exists when the collective is raised to a point where the main rotor blade angle of attack creates so much drag that all available engine power cannot maintain or restore normal operation rotor RPM.[7] Beyond this point, any further attempt to raise the collective will result in a reduction of main rotor RPM as the engine has no remaining power margin to overcome the drag on the blades. With a reduction of the main rotor RPM, there will be a reduction in lift being produced and a disproportionate reduction in the amount of anti‑torque thrust available to the tail rotor. In explaining the reduction in tail rotor thrust, Robinson stated:

Since thrust of the rotor is proportional to the square of RPM, and the tail rotor is operating at roughly 6 times the RPM of the main rotor, a small reduction in main rotor RPM leads to a large reduction in tail rotor thrust.

Overpitching can also occur if the pilot raises the collective lever at a rate that is faster than the correlator will open the throttle, while not compensating for the increased drag by manually increasing the throttle.

The pilot was confident that the throttle was set to 100% for the approach, however, they were not certain if the throttle was manipulated in the avoidance manoeuvre. The recommended technique for recovery from unanticipated yaw is to lower the collective to reduce torque and simultaneously increase throttle to over-ride the correlator, which would otherwise decrease the throttle when the collective is lowered.

Maintaining maximum available engine RPM ensures that the maximum power is available to the anti-torque system. During both approaches, the helicopter could be seen to drift with the wind. AC 90-95 advised that drifting with the wind results in a reduction in the effective translational lift[8] and a corresponding increase in the power demand and anti-torque requirements. This again could result in a decrease in the main rotor RPM and the corresponding anti‑torque thrust available.

Accident site

The ATSB attended the site and conducted an inspection of the wreckage (Figure 1). The helicopter had struck high and low-voltage power lines during the descent and came to rest on its left side, spanning a drainage culvert.

Inspection of the cockpit showed that there was full left pedal input. While the pedals could not be moved, a subsequent examination found this was due to airframe deformation attributed to the impact. Once adjusted, the pedals moved freely. The drive belts were intact and in place. Once the clutch was released, the main rotor rotated freely, and drive continuity was followed to the tail rotor.

The tail boom skin was disrupted in 2 locations but was still attached to the helicopter. The fracture surfaces on the drive shaft were consistent with overstress and attributed to the impact with terrain. Similarly, damage to the tail rotor gearbox housing showed evidence of uniform overstress attributed to the impact. A review of witness videos showed no evidence of tail boom disruption in flight and the engine could be heard to operate normally.

The main rotor blades showed evidence of low rotational energy with both blades still intact and connected to the hub. Additionally, no major ground scars were observed on-site. The pilot advised that the low rotor RPM horn sounded at approximately the same time the helicopter struck the powerlines.

The positions of the collective and the throttle were examined during the on-site inspection and the collective was found lowered with the half throttle set. It could not be determined from the onsite inspection what control inputs were applied prior to descent and it is likely that these controls were disrupted following the collision with terrain as the pilot fell in that direction across the controls.

Assessment of damage

No anti-torque, cyclic or collective control faults or other mechanical issues were found with the helicopter. Continuity in the anti-torque system and drive train were consistent with pilot report of no mechanical issues with the helicopter.

Similar occurrence

ATSB investigation AO-2017-054

On 17 May 2017, the pilot of a Robinson Helicopter R44 II, registered VH-MNU, was conducting aerial work at Moreton Island, Queensland with one passenger on board. The pilot departed for a local flight at about 1005 local time.  At about 1130, the helicopter was operating at approximately 50 ft above ground level and tracking in a south-westerly direction, at an airspeed of about 10 kt (and groundspeed of about 20 kt), when the pilot commenced a right turn. The pilot felt a loss of tail rotor effectiveness as the helicopter continued to yaw to the right and reported that they were unable to arrest the yaw with left pedal input.

The pilot applied forward cyclic to try to increase the helicopter’s forward speed and some right cyclic to try to follow the turn. As the helicopter turned back into wind and rotated through about 110°, the rate of yaw started to increase. The pilot then raised the collective in an attempt to increase the helicopter’s height above trees, which further increased the yaw rate due to the increase in torque.  The helicopter completed about 2 full rotations and reached about 80 ft above the ground, when the low rotor RPM warning horn sounded. The pilot immediately lowered the collective and the helicopter descended.  As the helicopter neared treetop height, the pilot deployed the emergency floats and the pilot raised the collective to cushion the impact. The pilot and passenger sustained minor injuries and the helicopter was substantially damaged.

Safety analysis

The pilot planned to land at a confined area that required them to approach the landing site over powerlines and a row of trees. This required the helicopter to be flown out of ground effect with a high-power setting and at slow forward air speed.

Considering the recorded Gosford weather observations of the wind from the north-east at 10 kt, the approach track placed the wind from a direction and at a speed known to be conducive to the onset of loss of tail rotor effectiveness (LTE) via both tail rotor vortex ring state and main rotor disc vortex interference (Figure 5). The yaw fluctuations experienced during the first approach were consistent with the onset of an unanticipated yaw but were not identified by the pilot.

Video footage of the accident sequence showed a right yaw with accelerating rotation, also consistent with the symptoms of an unanticipated yaw event.

Flying out of ground effect at a slow forward airspeed in proximity to obstacles placed the aircraft in a scenario that did not easily allow for recovery. It is likely that the initial actions by the pilot were consistent with the recommended recovery techniques. However, while setting 100% throttle provided maximum power-on rotor RPM and ensured the maximum anti‑torque thrust was available, it would also have maintained the torque inducing the yaw.

Further, consistent with the pilots account of the low rotor RPM horn activation and the audible reduction in main rotor RPM present in the video footage, raising of the collective to avoid obstacles during the attempted recovery, probably over-pitched the main rotor blades. The resulting decrease in both the main and tail rotor speed reduced the available anti‑torque thrust and increased the rate of descent.

In a situation where the time to respond is reduced, such as during an approach, following the recommended recovery technique greatly improves the likelihood of recovering controlled flight. However, based on the available height above obstacles and uncertainty around the actual control inputs made by the pilot, it could not be determined if application of the recommended recovery technique would have been effective in recovering the helicopter or if a collision was unavoidable.

The FAA helicopter flying handbook stated that a recovery path must always be planned, especially when terminating to an out of ground effect hover and executed immediately if an uncommanded yaw is evident. Terrain, obstacles, and people in the undershoot limited the available forced landing options to the pilot on this occasion.

Findings

ATSB investigation report findings focus on safety factors (that is, events and conditions that increase risk). Safety factors include ‘contributing factors’ and ‘other factors that increased risk’ (that is, factors that did not meet the definition of a contributing factor for this occurrence but were still considered important to include in the report for the purpose of increasing awareness and enhancing safety). In addition ‘other findings’ may be included to provide important information about topics other than safety factors. 

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

From the evidence available, the following findings are made with respect to the loss of control and collision with terrain involving VH-TKI on 15 November 2022.

Contributing factors

  • During approach to a confined area landing site, the helicopter experienced unanticipated right yaw, resulting in collision with powerlines and terrain.

Other findings

  • It could not be established if control of the aircraft was recoverable from the point in the approach that the unanticipated right yaw occurred.

Sources and submissions

Sources of information

The sources of information during the investigation included the:

  • pilot of the accident flight
  • chief pilot of Skyline Aviation
  • Bureau of meteorology
  • Robinson Helicopter Co. R44 Pilot Operating Handbook
  • accident witnesses
  • video footage of the accident flight
  • recorded data from the GPS unit in VH-TKI.

References

Civil Aviation Safety Authority. (2022). Advisory Circular AC 91-29 v1.1 Guidance for helicopters – suitable places to take-off and land. Civil Aviation Safety Authority.

Civil Aviation Safety Authority. (2019). Civil Aviation Safety Regulations 1998 - Part 91 (General operating and flight rules) Australian Government.

International Civil Aviation Organization. (2011). Manual of Aircraft Accident and Incident Investigation Part III: Investigation, Doc 9756, ICAO, Montréal.

Federal Aviation Administration. (1995). Advisory Circular AC 90-95 – Unanticipated right yaw in helicopters. Federal Aviation Administration.

Federal Aviation Administration. (2019). Helicopter flying handbook. U.S Department of Transportation.

Robinson Helicopter Company. (2021). R44 Pilot’s Operating Handbook. Robinson Helicopter Company.

Robinson Helicopter Company. (2021). Safety Notice SN-42 – Unanticipated yaw. Robinson Helicopter Company.

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 of the accident flight
  • the chief pilot of Skyline Aviation
  • Robinson Helicopter Company
  • United States National Transportation Safety Board.

Submissions were received from:

  • the chief pilot of Skyline Aviation
  • Robinson Helicopter Company

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 2023

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[1]     Autorotation: Autorotation is a condition of descending flight where, following engine failure or deliberate disengagement, the rotor blades are driven solely by aerodynamic forces resulting from rate of descent airflow through the rotor. The rate of descent is determined mainly by airspeed.

[2]     Notice to Airmen (NOTAM): A notice distributed by means of telecommunication containing information concerning the establishment, condition or change in any aeronautical facility, service, procedure or hazard, the timely knowledge of which is essential to personnel concerned with flight operations.

[3]     Ceiling and visibility okay (CAVOK): visibility, cloud and present weather are better than prescribed conditions. For an aerodrome weather report, those conditions are visibility 10 km or more, no significant cloud below 5,000 ft, no cumulonimbus cloud and no other significant weather.

[4]     Out of ground effect: helicopters require less power to hover when in ‘ground effect’ then when out of ‘ground effect’ due to the cushioning effect created by the main rotor downwash striking the ground. The height of ‘ground effect’ is usually defined as more than one main rotor diameter above the surface.

[5]     Azimuth: An azimuth is an angle measured clockwise from the south or north.

[6]     Cyclic: a primary helicopter flight control that is similar to an aircraft control column. Cyclic input tilts the main rotor disc, varying the attitude of the helicopter and hence the lateral direction.

[7]     International Civil Aviation Organization (ICAO) Manual of Aircraft Accident and Incident Investigation. Chapter 15: Helicopter investigation.

[8]     Effective translational lift: Increase in the efficiency of a rotor achieved as it clears its own tip vortices and enters undisturbed air. The increased efficiency of the blade results in an increase in lift with an associated reduction in power demand on the antitorque system.

Occurrence summary

Investigation number AO-2022-060
Occurrence date 19/11/2022
Location Forresters Beach
State New South Wales
Report release date 09/06/2023
Report status Final
Investigation level Short
Investigation type Occurrence Investigation
Investigation status Completed
Mode of transport Aviation
Aviation occurrence category Collision with terrain
Occurrence class Accident
Highest injury level Minor

Aircraft details

Manufacturer Robinson Helicopter Co
Model R44
Registration VH-TKI
Serial number 40
Sector Helicopter
Operation type Part 91 General operating and flight rules
Departure point Jilliby
Destination Forresters Beach
Damage Substantial

About mandatory occurrence reporting 

Typically, the ATSB safety reporting team receives more than 17,000 notifications of safety occurrences each year, spread over aviation, marine and rail.

While there may be duplicate notifications of the same occurrence and many of the notifications submitted are about matters not required to be reported under the Transport Safety Investigation Act 2003, each one is reviewed and recorded.  

The TSI Act requires any responsible person who has knowledge of any accident or serious incident (or any immediately reportable matter) to report it as soon as it is reasonably practicable.

Immediately reportable matters also require a written notification within 72 hours, as do safety incidents (or routine reportable matters).  

While the terms of this requirement may seem broad, the Transport Safety Investigation Regulations 2021 (TSI Regulations) provide a list of persons who, by the nature of their qualifications, experience or professional association, would be likely to have knowledge of an immediate or routine reportable matter for their mode of transport.  

In addition, responsible persons are not required to report a transport safety matter if they believe, on reasonable grounds, that another responsible person has already reported, or is in the process of reporting, that matter.  

The ATSB maintains a 24-hour service to receive notifications, including a toll-free telephone number (for immediately reportable matters).

For aviation, a secure online form(Opens in a new tab/window) for written notifications is available on the ATSB website.

In rail, all immediately notifiable matters are reported to the Office of the National Rail Safety Regulator(Opens in a new tab/window) (ONRSR), which then reports to the ATSB. The written notifications are provided to the ATSB via reporting to ONRSR.

In marine, both immediately reportable and routine reportable matters are reported to the ATSB via AMSA(Opens in a new tab/window).  

While not all reported occurrences are investigated, the details of each occurrence are retained within the ATSB occurrence database. These records are a valuable resource, providing a detailed portrait of transport safety in Australia. The searchable public version of the aviation occurrence database is available on the ATSB website and contains data from July 2003 onwards. The online database is used by industry, academics, the media and regulators to search and research past events.

Investigative response prioritisation

The level of investigative response is determined by resource availability and factors such as those detailed below. These factors (expressed in no particular order) may vary in the degree to which they influence ATSB decisions to investigate and respond. Factors include:  

  • the anticipated safety value of an investigation, including the likelihood of furthering the understanding of the scope and impact of any safety system failures  
  • the likelihood of safety action arising from the investigation, particularly of national or global significance  
  • the existence and extent of fatalities/serious injuries and/or structural damage to transport vehicles or other infrastructure  
  • the unique value an ATSB investigation will provide over any other investigation by industry, regulators or police  
  • the obligations or recommendations under international conventions and codes  
  • the nature and extent of public interest – in particular, the potential impact on public confidence in the safety of the transport system  
  • the existence of supporting evidence, or requirements, to conduct a special investigation based on trends  
  • the relevance to identified and targeted safety programs  
  • the extent of resources available, and projected to be available, in the event of conflicting priorities  
  • the risks associated with not investigating – including consideration of whether, in the absence of an ATSB investigation, a credible safety investigation by another party is likely  
  • the timeliness of notification  
  • the training benefit for ATSB investigators.  

Aviation broad hierarchy

1) Passenger transport operations and medical transport operations (including positioning flights): 

  • air transport operations (scheduled or non-scheduled), balloon transport operations, mining fly-in-fly-out operations, scenic flights/joy flights, parachuting operations, future advanced air mobility passenger carrying operations, and aerial work operations that carry passengers who are not crew members 
  • flights formerly known as air ambulance operations, Royal Flying Doctor Service flights and patient transport/transfer services using aircraft operated by state and territory ambulance services. 

2) Non-passenger commercial aircraft operations (including positioning flights): 

  • aerial work operations such as surveying, spotting, surveillance, agricultural operations, aerial photography; search and rescue operations; flying training activities 
  • cargo transport operation 
  • large (greater than 150 kg) or medium (25–150 kg) RPAS or RPAS which is type certificated. 

3) Recreational flying, ‘private’ general aviation, and flights where the pilot shares equally in costs with passengers (cost sharing).

4) Higher-risk personal recreation/sports aviation/experimental aircraft operations. 

5) Small and very small RPA, uncrewed balloons. 

The ATSB endeavours to investigate all fatal accidents involving VH-registered powered aircraft subject to the potential transport safety learnings and resource availability.

Marine broad hierarchy

The ATSB allocates its investigative resources to be consistent with the following broad hierarchy of marine operation types:

  • passenger operations
  • freight and other commercial operations
  • non-commercial operations.

Rail broad hierarchy

The ATSB allocates its investigative resources to be consistent with the following hierarchy of rail operation types:

  • mainline operations that impact on passenger services
  • freight and other commercial operations
  • non-commercial operations.

About ATSB investigation reports and terminology

ATSB investigation reports

The ATSB will release a final report at the conclusion of an investigation, detailing contributing factors, safety issues and other findings. However, at any time during the course of an investigation, should we uncover safety critical information we will immediately share that with relevant parties so they can take appropriate safety action.

Depending on the complexity of the occurrence and the scope of the investigation, the ATSB may also publish preliminary and interim reports.

Preliminary reports detail factual information determined in an investigation’s initial evidence collection phase and areas of ongoing investigation. They are typically released 1–4 months after the initial occurrence. 

Interim reports detail more extensive factual information and outline areas of ongoing investigation. 

During the course of an investigation, the ATSB also provides brief factual updates on an investigation's progress on our website.

Either in conjunction with a report release or at any time during an investigation, the ATSB may also issue a safety advisory notice to relevant organisations and industry sectors to highlight a safety issue or concern and advising that relevant parties take safety action where appropriate.

Final report structure

ATSB occurrence investigation final reports are organised with regard to international standards or instruments, as applicable, and with ATSB procedures and guidelines. Reports normally contain the following sections:

  • Investigation summary—summarises the occurrence (or other transport safety matter), the investigations findings, any safety action taken as a result, and highlights broader safety messages.  
  • The occurrence—describes the sequence of events related to the occurrence and, if relevant, the consequences in terms of injuries and damage.
  • Context—details the evidence collected during the investigation that is necessary to help the reader understand the occurrence and safety analysis, or the broader safety issues for research purposes.
  • Safety analysis—outlines how the evidence justifies the investigation findings.
  • Findings—the contributing factors, other factors that increased risk and other findings identified during the investigation and discussed in the safety analysis.
  • Safety issues and actions—a summary of the safety issues identified during the investigation and details of what safety action has been taken, or is planned to be taken, by relevant parties to address those issues.
  • Appendices—additional information that supports the report, for example, specialist reports on materials failure or flight data analysis.

Report terminology

Occurrence: a transport accident or incident.

In a safety context, accidents and incidents have specific definitions in relevant legislation, standards and other publications. In general, an accident is defined as an event that results in adverse consequences (that is, more than minor injuries and/or damage), whereas an incident is defined as an event that had the potential to result in adverse consequences. 

For example, the Transport Safety Investigation Act 2003 provides the following definition of an accident:

… an investigable matter involving a transport vehicle where:

(a) a person dies or suffers serious injury as a result of an occurrence associated with the operation of the vehicle; or

(b) the vehicle is destroyed or seriously damaged as a result of an occurrence associated with the operation of the vehicle; or

(c) any property is destroyed or seriously damaged as a result of an occurrence associated with the operation of the vehicle.

Safety factor: an event or condition that increases safety risk. In other words, it is something that, if it occurred in the future, would increase the likelihood of an occurrence, and/or the severity of the adverse consequences associated with an occurrence. 

Safety factors can be classified as to whether they are contributing factors or other factors that increased risk. They can also be classified in terms of the levels of the ATSB analysis model, as shown in the following diagram.

ATSB safety factor analysis model

The following diagram provides some examples of the types of factors that may be identified at each of the levels.

Types of safety factors that may be identified at each of the levels

Contributing factor: a safety factor that, had it not occurred or existed at the relevant time:

  • the occurrence would probably not have occurred, or
  • the adverse consequences associated with the occurrence would probably not have occurred or have been as serious, or
  • another contributing factor would probably not have occurred or existed.

The ATSB definition is based on detailed research considering how causation and contribution is defined in various fields. Further information is provided in the ATSB research report AR-2007-053, Analysis, Causality and Proof in Safety Investigations.

To determine whether an event or condition is a contributing factor, the ATSB conducts a test for existence and a test for influence. The term ‘probable’ indicates the standard of proof required for passing these tests. This standard sits between the legal standards of ‘beyond reasonable doubt’ and the ‘balance of probabilities’. Further discussion of probability definitions is provided below. 

Other factor that increased risk: a safety factor that did not meet the definition of contributing factor but was still considered to be important to communicate in an investigation report in the interests of improved transport safety.

Other factors that increased risk can be safety factors for which there is sufficient evidence to conclude they probably did not contribute (or have an influence) on this occasion. 

They also include safety factors for which a reliable decision about whether they contributed could not be made based on the available evidence.

In other words, just because a safety factor was classified as an other factor that increased risk, this does not necessarily mean it did not contribute. Rather, on many occasions, it just means that there was insufficient evidence to conclude that it contributed. 

As stated in the Transport Safety Investigation Act (2003) section 12AA (Function of the ATSB):

(1)  The ATSB’s function is to improve transport safety by means that include the following …

(b)  independently investigating transport safety matters;

(c)  identifying factors that:

   (i)  contribute, or have contributed, to transport safety matters; or

   (ii)  affect, or might affect, transport safety;

(d)  communicating those factors to relevant sectors of the transport industry and the public … 

(e)  reporting publicly on those investigations …

The ‘other factors that increase risk’ are synonymous with the factors that ‘affect, or might affect, transport safety’.

It is common practice for safety investigations (as well as Coronial inquiries) to include contributing factors and other safety factors that are identified during an investigation. How such non-contributing but safety-relevant findings are presented in investigation reports varies. The ATSB and some other agencies have chosen to do this explicitly within the findings section of the report.

Other finding: any finding, other than those associated with safety factors, considered important to include in the findings section of an investigation report. 

Such findings may resolve ambiguity or controversy, describe possible scenarios or safety factors when firm safety factor findings were not able to be made, note events or conditions which 'saved the day' or played an important role in reducing the risk associated with an occurrence, or highlight something that limited the scope or effectiveness of the investigation.

Safety issue: a safety factor that:

  • can reasonably be regarded as having the potential to adversely affect the safety of future operations, and
  • is a characteristic of an organisation or a system, rather than a characteristic of a specific individual, or characteristic of an operational environment at a specific point in time.

Safety issues will generally refer to problems with an organisation’s risk controls, or a variety of internal and external organisational influences that impact on the effectiveness of an organisation’s risk controls. They describe conditions that can be and should be rectified to enhance safety. 

Both contributing factors and other factors that increased risk can include safety issues. Only relevant conditions that are assessed as being above a defined risk level at the time of the occurrence are classified as safety issues.

Safety action: the steps taken or proposed to be taken by an organisation, agency or other party in response to a safety issue. Safety action includes proactive safety action taken by a relevant organisation or party, safety recommendations issued by the ATSB, and safety advisory notices issued by the ATSB.

Safety recommendation: a formal safety recommendation made either during or at the end of an investigation, where the ATSB remains concerned that a safety issue has yet to be adequately addressed by the relevant organisation.

Probability expressions

During safety investigations, investigators can rarely use mathematical probability as a basis for making findings due to the nature of the available evidence. Instead, various terms are used to represent the investigators’ understanding of the level of likelihood (for example, ‘probable’ or ‘very likely’). Such terms are known as ‘verbal probability expressions’. 

The list below presents the verbal probability expressions used by the ATSB in our investigation reports to describe the degree of likelihood or chance that something was true (such as something existing, something influencing something else, or something having a specified risk level). 

  • Virtually certain (almost certain) – 99% or more
  • Extremely likely – 95% or more
  • Very likely – 90% or more
  • Likely (or probable) – 66% or more
  • About as likely as not – 33% to 66%
  • More likely than not – more than 50%
  • Unlikely (or improbable) – 33% or less
  • Very unlikely – 10% or less
  • Extremely unlikely –­ 5% or less
  • Exceptionally unlikely – 1% or less.

These definitions were developed by the International Governmental Panel on Climate Change (IPCC). The IPCC definitions have been based on a substantial amount of discussion involving a range of different types of experts from many countries. The definitions are also broadly consistent with previous research into how people use different verbal probability expressions.

The expressions only provide an indication of meaning, not a detailed prescription. In almost all situations, selecting the most appropriate expression is a matter of judgement, based on the available evidence, rather than a matter of precise measurement.

Gender-neutral language in ATSB reports

All ATSB reports are de-identified. On the basis that gender‑specific language can lead to the identification of individuals, in 2020 the ATSB Commission adopted a policy of using gender‑neutral language in ATSB investigation reports.

In the report writing process, care is taken to ensure context and meaning are not lost.

Occurrence investigation levels

The ATSB conducts different levels of investigation according to the anticipated scope and scale of the work required to determine the contributing factors to a safety occurrence.

Occurrence briefs

Occurrence briefs provide the opportunity to share important safety messaging and information with industry and the public in the absence of an investigation. They are a short factual summary to detail the circumstances surrounding an occurrence, which only uses information gathered during the initial notification, and from any follow-up information with relevant parties.

Because occurrence briefs are not investigations under the Transport Safety Investigation Act 2003, the information within them is de-identified. While they do not include any analysis, findings, safety issues, safety actions or recommendations, occurrence briefs do provide an additional opportunity to learn from the experiences of others.

Occurrence briefs can be produced by ATSB Transport Safety Investigators or members of our Safety Reporting Team (all of whom have significant transport industry experience).

Short investigations

Short investigations provide a summary and analysis of commonly occurring transport safety accidents and incidents. Investigation activity includes sourcing imagery and documentation of any transport vehicle damage and/or accident site, conducting interviews with involved parties, and the collection of documents such as procedures and internal investigations by manufacturers and operators.

Short investigation reports include a description of the sequence of events, limited contextual factual information, a short analysis, and findings. Findings include safety factors (the events and conditions that increased the risk of incident or accident happening) but only examine the actions and conditions directly relating to the occurrence and any proactive safety actions taken.

Defined investigations

Defined investigations look at transport safety accidents and incidents of a more complex nature than short investigations, and seek to identify systematic safety issues that reveal underlying causes of an occurrence. They involve several ATSB resources and may involve in-the-field activity or be an office-based investigation. Evidence collected can include recorded flight and event information, multiple interviews, analysis of similar occurrences, and a review of procedures and other risk controls related to the occurrence.

Defined investigation reports include an expanded analysis to support the broader set of findings within the report and may include safety factors not relating directly to the occurrence. Defined investigations may also identify safety issues (safety factors with an ongoing risk) relating to ineffective or missing risk controls. The report also identifies safety issues, along with proactive safety action taken by industry and ATSB safety recommendations.

Systemic investigations

Systemic investigations can involve in‑the‑field activity, and a range of ATSB and possibly external resources. They have a broad scope and involve a significant effort collecting evidence across many areas. The breadth of the investigation will often cover multiple organisations. Occurrences and sets of transport safety occurrences investigated normally involve very complex systems and processes.

In addition to investigating failed and missing risk controls, systemic investigations may also investigate the organisational processes, systems, cultures and other factors that relate to those risk controls, including from the operator, regulator, and certifying and standards authorities. Systemic investigations result in substantial reports, often with several safety issues identified.

Systemic investigations were previously known as 'complex' investigations. The change in terminology more accurately reflects the broad scope and systems-level complexities involved in these investigations.

Major investigations

In the event of a significant accident (potentially involving a large number of casualties), the ATSB would conduct a major investigation. Major investigations would likely involve significant ATSB and external resources and potentially require additional one-off government funding.

 

Reporting requirements for RPA

New reporting requirements for safety occurrences involving remotely piloted aircraft (or drones) took effect on 30 September 2021.

The Transport Safety Investigation Regulations 2021(Opens in a new tab/window) require the reporting of certain transport safety occurrences to the ATSB as immediately or routine reportable matters, and introduced updated requirements for operators of certain types of remotely piloted aircraft (RPA) to make reports to the ATSB.

Recognising the range of different types of RPA and their uses, the regulations categorise relevant RPA as type 1 or type 2 RPA.  

RPAs that have been certified against relevant airworthiness standards (type certification), large (greater than 150kg) and medium RPAs (more than 25kg but not more than 150kg) are defined as type 1 and are an emerging form of commercial aviation that will benefit from investigation into systemic safety issues to help prevent future accidents.

Type 2 RPA are defined as those RPA that are not type 1, excluded or micro RPA (gross weight of not more than 250 grams) and have fewer reporting requirements. This distinction is made on the basis that ATSB investigations are unlikely for these operations unless there is serious risk of harm to people or significant third-party property.

RPAs that are not type 1 or type 2 including excluded or micro RPA have no reporting requirements.

Mandatory reporting for certain occurrences involving type 1 and type 2 RPA allows the ATSB to properly measure, investigate and report on safety trends in the RPA sector.

Making a report to the ATSB is not a time-consuming process, and the ATSB investigates incidents from a ‘no-blame’ perspective, prioritising improved safety outcomes.

Who is affected?

In order to provide an efficient and effective safety framework, the regulations define two types of RPAs which are subject to specific reporting requirements.

Type 1 RPAs are those which are type certified, large (over 150 kg) or medium (25 kg to 150 kg) RPA.

Type 2 RPAs are those that are not Type 1, and are not an excluded or micro (under 250 g) RPA.

Type 1 operators are required to immediately report to the ATSB RPA occurrences involving:

  • death or serious injury;
  • accidents;
  • loss of a separation standard with aircraft; and,
  • serious damage to property.

Less serious incidents and occurrences are required to be reported to the ATSB within 72 hours

Occurrences involving Type 2 RPAs generally only need to be immediately report to the ATSB if they involve death or serious injury, while less serious incidents and damage to the RPA will need to be reported within 72 hours.

RPA checklist

RPAS checklist

Make a report to the ATSB here.

Naming organisations in reports

ATSB policy provides for identifying most organisations in its transport safety investigations. Most organisations directly involved in any aviation occurrence investigated by the ATSB are identified in the report and on the investigation web page.

The policy ensures the ATSB’s compliance with the International Civil Aviation Organization’s recommended practices. It also ensures that the ATSB has a consistent and transparent approach across all of its aviation, rail and marine safety investigations.

Operators and other organisations can be assured that it is not a function of the ATSB to apportion blame or determine liability. Including the name of the organisation does not imply any adverse inferences.

Which organisations are identified

For aviation, all operators and regulators are identified.

For marine, all ship owners, ship management companies and the regulator are identified.

For rail, rail transport operators (rail infrastructure managers and/or rolling stock operators) and regulators are identified.

Other large organisations that contributed substantively to the occurrence will also be mentioned. The exception to the above policy will be where the operator is an individual or an individual’s name is the company name. Consistent with the Transport Safety Investigation Act 2003, the ATSB does not name individuals in its final reports.

Are there any exceptions?

If an operator or organisation had a passive or third-party involvement in an occurrence, the ATSB will not name that operator in the investigation report or published information.

Operators and other organisations will not be named in investigation report titles.

This policy applies to safety occurrences investigated by the ATSB from 1 July 2017. Any incident or accident that occurred before 1 July 2017 was treated under the previous policy.

How will an organisation know if they’re named?

The ATSB provides advance copies of its investigation reports to all organisations involved in a transport safety occurrence. This ensures organisations are aware of, and have the opportunity to provide feedback on, the report’s contents before it is made public.

Weather related accidents remain a significant concern – ATSB Chief Commissioner

Provides an indication of the weather just prior to the accident.

Key points

  • ATSB has released a second weather-related investigation final report from a fatal general aviation accident this month;
  • It is highly likely cloud and visibility conditions resulted in the pilot experiencing a loss of visual reference and probably becoming spatially disoriented;
  • Pushing on into cloud and low visibility when you do not hold the appropriate rating and experience in an aircraft that is not appropriately equipped carries a significant risk of severe spatial disorientation.

Weather-related accidents remain one of the most significant causes of fatal accidents in general aviation, says Australian Transport Safety Bureau Chief Commissioner Angus Mitchell.

Mr Mitchell reiterated the concern with the release of the ATSB’s final report from the investigation into a fatal helicopter accident in Kosciuszko National Park on 3 April this year.

One of 7 helicopters taking part in a flying tour, a Bell 206L-4 LongRanger, registered VH-PRW, departed with a pilot and passenger on board, for a visual flight rules (VFR) flight from a private property at Majura, near Canberra, to Mangalore, Victoria, with a planned refuelling stop in Tumut.

The weather forecast indicated low cloud, rain and associated reduced visibility on the planned route, and 2 of the helicopters diverted to Wagga Wagga, due to weather while 4 others landed near Wee Jasper, to Canberra’s north-west.

The pilot of VH-PRW elected to continue until they encountered poor weather conditions and landed in open terrain alongside Long Plain Road in the Brindabella region, west of Canberra and to the south of Wee Jasper, shortly before noon, the investigation report details (pictured).

About three hours later, at 1453 local time, the helicopter departed the interim landing site at low level, in overcast conditions with low cloud and light rain.

At about 1525, recorded data showed that the helicopter commenced a rapid climb and shortly after, entered a steep left descending turn which continued until it impacted terrain at an elevation of 4,501 ft.

A search was initiated the next day with the accident site located later that evening. The helicopter was destroyed, and both occupants were fatally injured.

The pilot held a private pilot licence (helicopter) and did not hold an instrument rating, and the helicopter was not approved for instrument flight.

“The pilot initially made the right decision and landed the helicopter,” noted Mr Mitchell.

“However, you’re only as safe as your last decision, and the pilot’s then decision to launch again and push on – for reasons that we will never fully comprehend – put the helicopter into a dangerous environment with powerful and misleading orientation sensations and no visual cues.

“It is highly likely these cloud and visibility conditions resulted in the pilot experiencing a loss of visual reference and probably becoming spatially disoriented. Tragically, this led to a loss of control of the helicopter and an unsurvivable collision with terrain.”

This investigation report is the second the ATSB has released this month into an accident where a VFR pilot likely encountered low visibility conditions, before becoming spatially disorientated leading to a loss of control of their aircraft.

The ATSB is also currently investigating other fatal accidents where the weather conditions are under consideration, including the collision with terrain of an Airbus Helicopters EC130 T3 near Mount Disappointment, Victoria on 31 March 2022 where a pilot and four passengers were killed.

In 2018, following the final report release into another fatal helicopter accident involving VFR into IMC conditions, the ATSB, in conjunction with CASA and the Australian Helicopter Industry Association launched the ‘Don’t Push it, LAND IT – when it’s not right in flight’ safety campaign encouraging helicopter pilots to conduct a precautionary landing rather than push on into abnormal situations.

“Don’t push on,” Mr Mitchell urged visual flight rules pilots.

“Pushing on into cloud and low visibility when you do not hold the appropriate rating and experience carries a significant risk of severe spatial disorientation and can affect any pilot, no matter what their level of experience.”

 In the decade from 1 November 2012 to 1 November 2022, 97 VFR into IMC occurrences in Australian airspace were reported to the ATSB. Of those, 11 were accidents resulting in 22 fatalities.

Mr Mitchell stressed the importance of planning ahead to avoid deteriorating weather.

“Ensure you have alternate plans in case of an unexpected deterioration in the weather and make timely decisions to turn back or divert,” he said.

“And know your limits. As a visual flight rules pilot the use of a ‘personal minimums’ checklist helps to control and manage flight risks through identifying risk factors that include marginal weather conditions.

“The ATSB continues to see this category of accident happening,” Mr Mitchell noted.

“In fact, this is the second final report we’ve published this month into a fatal accident where a visually rated pilot has likely become spatial disorientated and collided with terrain.

“Please, only fly in environments that do not exceed your capabilities, and most importantly, don’t push it, land it. Or, just don’t go.”

Read the final report: VFR into IMC and collision with terrain involving Bell Helicopter 206L-4, VH-PRW 33 km north‑west of Adaminaby, New South Wales, on 3 April 2022

Also read the ‘Avoidable Accidents’ publication Accidents involving Visual Flight Rules Pilots in instrument Meteorological Conditions

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