Aviation safety investigations & reports

In-flight break-up involving Robinson R44 Raven I, VH-HGU 31 km east of Goulburn Airport, New South Wales, on 2 December 2020

Investigation number:
Status: Completed
Investigation completed
Phase: Final report: Dissemination Read more information on this investigation phase


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What happened

On the afternoon of 2 December 2020, a Robinson Helicopter Company (RHC) R44 Raven I, registered VH-HGU, departed Goulburn Airport, New South Wales with a student pilot and instructor on board. The helicopter flew east, and the last recorded automatic dependent surveillance broadcast (ADS-B) detected it descending into a valley in the Bungonia State Conservation Area. A search commenced when the helicopter did not return as expected, and the wreckage of VH-HGU was found in a valley, approximately 4 km north-west of its last ADS-B transmission. Both pilots were fatally injured, and the helicopter was destroyed.

What the ATSB found

Wreckage examination indicated that while flying in the vicinity of the valley, the helicopter entered a low-G condition due to turbulence, inappropriate control inputs, or a combination of both. This condition, probably in combination with inappropriate recovery control inputs resulted in extreme teetering of the main rotor. A mast bump occurred as a result, and the helicopter subsequently broke up in flight.

An intense post-impact fire prevented a complete examination of the wreckage. However, the evidence available gave no indication that the helicopter was operating abnormally prior to the in‑flight break-up.

The circumstances leading to in-flight break-ups from mast bumping and extreme teetering are usually not identified. While the fire would likely have prevented data recovery in this case, the inclusion of readily available cockpit video recorders on helicopters with semi-rigid rotor heads would provide valuable insights into low-G mast bumping events, which could help to prevent future occurrences.

What has been done as a result

The operator has introduced a limit of 6 consecutive training days. In addition, an online flight and duty monitoring system will be used to assess and adjust duty hours for instructors and students.

Since the occurrence, RHC has introduced cockpit video/audio recorders as standard equipment on new R44 helicopters, having previously been available on R66 models. The recorders are optional on R22 models, but will be standard equipment in 2023, with retrofit kits made available.

Safety message

Low-G conditions can be catastrophic for helicopters with semi-rigid rotor heads. A pilot’s ability to recover from low-G remains uncertain, though all parties agree that it is dependent on airspeed and time available. Pilots must therefore avoid low-G situations, and take the following actions to mitigate risk:

  • Make a careful study of the terrain, forecasts and observations applicable to the proposed flight to identify significant weather such as fronts or mechanical turbulence and avoid flying in those conditions.
  • Reduce airspeed when encountering significant turbulence.
  • Avoid flight downwind of hills, ridges or other potential sources of turbulence, particularly during changing or unpredictable weather conditions.
  • Allow plenty of altitude so that there is enough time for recovery from unexpected flight conditions.
  • Use slow and small control inputs.

Recording devices have long been recognised as an invaluable tool for investigators in identifying the factors behind an accident, and their contribution to aviation safety is irrefutable. While not required by regulations, operators should consider the benefits of installing such devices.


Download Final Report
[Download  PDF: 2.1MB]

The occurrence


Safety analysis


Safety action


Sources and submissions

About the ATSB


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

On 2 December 2020, at 1558 Eastern Daylight‑saving Time[1] a Robinson Helicopter Company (RHC) R44 Raven I, registered VH-HGU, departed Goulburn Airport, New South Wales with a trainee pilot and an instructor on board. The helicopter flew east from Goulburn Airport, and the last recorded automatic dependent surveillance broadcast (ADS-B) detected it descending into a valley in the Morton National Park at 1611.

Later that evening, when VH-HGU had not returned to Goulburn as expected, the chief pilot began an aerial search of the training area in another helicopter. The wreckage of VH-HGU was found in a valley, approximately 4 km north‑west of its last ADS-B transmission.

Wreckage examination indicated that, during the accident sequence, the main rotor struck the helicopter’s fuselage in flight. The uncontrollable aircraft subsequently collided with terrain. Both pilots were fatally injured and the helicopter was destroyed.

The engine and fuselage were exposed to a fire at the main wreckage site, which self‑extinguished before emergency services arrived. Figure 1 shows the direction and location of the helicopter’s last detected ADS-B transmission and the wreckage trail orientation.

Figure 1: Wreckage trail and final ADS-B transmission from VH-HGU

Wreckage trail and final ADS-B transmission from VH-HGU

The aircraft track at its last transmission point was calculated from ADS-B data, while the direction at impact was estimated based on the direction of wreckage and damage to trees around the accident site.

Source: Google earth, modified by ATSB


Pilot information

The instructor held a Grade 3 helicopter flight instructor rating, and had 690 hours of flying experience, predominantly in R44 helicopters.

The trainee pilot was undergoing intensive flight training for the issue of a private pilot licence and was 11 days into the course with the operator at the time of the accident. The trainee had accrued a total of 38 hours of dual flying on VH‑HGU. The trainee pilot’s first solo flight was conducted on the morning of the accident.

Aircraft and maintenance

The Robinson R44 is a four-seat, single piston engine helicopter, first certified in December 1992. In January 2000, RHC introduced the R44 Raven I. At the end of 2020, there were 566 R44 helicopters on the Australian civil aircraft register.

The R44 Raven I helicopter involved in the accident, serial number 2615, was built in May 2020 in the United States. The helicopter was first placed on the Australian register as VH-HGU on 10 July 2020. VH-HGU was being maintained in accordance with the RHC R44 manual suite. The most recent maintenance release was not recovered from the wreckage, but the helicopter had an estimated 150 hours total time in service.

On 14 October 2020, RHC issued a safety alert for engine intake valves installed on O-540-F1B5 engines. RHC reported they had been advised of burned intake valves on engines whose serial number ended in ‘40E’, with less than 500 hours’ time-in-service, which included VH-HGU. The alert stated:

Pilots should observe the following precautions:

1.Perform a complete run up and stabilized hover check prior to every flight. Do not initiate flight if there is any indication of engine roughness or sudden yaw.

2. If engine roughness or a sudden yaw occurs in flight, land as soon as practical and be prepared to land immediately.

3. Following any engine roughness or a sudden yaw, have a mechanic check valve condition before further flight. The mechanic should listen for sound of leakage at each intake valve while performing a compression check. Any intake valve with audible leakage requires repair prior to further flight. Check may be done with engine hot or cold.

A periodic inspection of VH-HGU was completed on 18 November 2020, at 100.57 hours total time in service. The intake valves were inspected and the valve covers were reinstalled with new gaskets. A compression check was conducted and no issues were identified.

Meteorological information

The two closest automatic weather stations showed significantly different weather 1 hour prior to, and at the time of the accident.

The half-hourly weather report at Goulburn Airport (31 km west of the accident site) recorded the wind from a north-westerly direction, up to 9 kt. The visibility remained greater than 10 km, and the temperature was 25°C. There was no other significant weather observed.

The half-hourly weather report at Moss Vale (43 km north-east of the accident site) recorded the wind from an easterly direction, up to 14 kt.

Based on the Moss Vale observations, a special weather report was first issued at 1538, due to a significant deterioration of weather conditions in the area. These conditions continued for several hours. A layer of broken [2] cloud commenced descending to 1,100 ft AMSL, with a second layer of overcast cloud descending to 1,600 ft AMSL. The temperature reduced to 16°C, with the dew point also reducing to 12°C.

Further investigation

To date, the ATSB has:

  • attended the accident site on two occasions for wreckage assessment and evidence collection
  • completed a subsequent examination of the helicopter’s engine and tail rotor driveshaft
  • conducted interviews with relevant parties, including the operator.

The investigation is continuing and will include:

  • consideration of factors that contributed to a rotor blade impacting the fuselage in flight, such as turbulence, pilot input, engine issues, and aircraft controllability
  • a review of the performance and handling characteristics of the helicopter
  • analysis of the weather conditions at the time of the accident
  • detailed technical examination of the engine and other retained components/electronic devices
  • a review of available training and aircraft maintenance documentation
  • assessment of related occurrences in Australia and overseas.

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.


The ATSB would like to acknowledge the significant assistance provided by the New South Wales Police Force during the initial investigation response.



  1. Eastern Standard Time (EST): Coordinated Universal Time (UTC) + 10 hours.
  2. Cloud cover: in aviation, cloud cover is reported using words that denote the extent of the cover –‘broken’ indicates that more than half to almost all the sky is covered, and ‘overcast’ indicates that all the sky is covered.
General details
Date: 02 December 2020   Investigation status: Completed  
Time: 16:30 EDT   Investigation level: Defined - click for an explanation of investigation levels  
Location   (show map): 31 km east of Goulburn Airport   Investigation phase: Final report: Dissemination  
State: New South Wales   Occurrence type: In-flight break-up  
Release date: 06 April 2022   Occurrence category: Accident  
Report status: Final   Highest injury level: Fatal  

Aircraft details

Aircraft details
Aircraft manufacturer Robinson Helicopter Co  
Aircraft model R44  
Aircraft registration VH-HGU  
Serial number 2615  
Operator Hughes Helicopters  
Type of operation Flying Training  
Sector Helicopter  
Damage to aircraft Destroyed  
Departure point Goulburn Airport, New South Wales  
Destination Goulburn Airport, New South Wales  
Last update 06 April 2022