Aviation safety investigations & reports

Loss of control in flight involving Leonardo Helicopters AW139 helicopter, VH-YHF, near Adelaide River mouth, 38 km ENE of Darwin, Northern Territory, on 13 May 2018

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

Final Report

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What happened

At 2000 Central Standard Time on 13 May 2018, the crew of a Leonardo Helicopters AW139, registered VH-YHF, departed Darwin, Northern Territory, to search for an active emergency position-indicating radio beacon (EPIRB). The crew flew under night visual flight rules with support of a night vision imaging system.

During an approach to a potential EPIRB target, smoke from nearby bushfires affected visibility and the helicopter developed an uncommanded high rate of descent. The Aircrew Officer, in the rear of the helicopter, called ‘Climb! Climb! Climb!’, and the pilot regained control with a rehearsed recovery drill. During the recovery procedure, the power demand exceeded airframe limitations. This exceedance went undetected, and the helicopter was flown on a second sortie that same evening.

What the ATSB found

The pilot entered instrument meteorological conditions during approach, and lost control of vertical speed. The helicopter descended to 31 ft above ground level during the event. Reversion to standard patter and practiced drills allowed the crew to recover the situation and avert an accident.

Two layers of protection available to the crew of the helicopter were not used. Flight instruments were not referred to in the incident approach, and a crewmember trained to support the pilot in monitoring the approach was required to be in the rear of the aircraft.

A main gearbox over-torque of 159.5 per cent occurred during the recovery. The crew could not determine the magnitude of the potential over-torque after the event. Subsequently the aircraft remained in service in a condition of uncertain airworthiness.

What has been done as a result

CareFlight has established three main controls aiming to prevent reoccurrence:

  • Stabilised Approach Criteria was written into standard operating procedures, requiring an immediate go-around if the aircraft leaves a prescribed range of approach parameters.
  • Controlled flight into terrain (CFIT) avoidance training was incorporated into the ground-based training syllabus.
  • Improved advice on use of auto hover functions was written into aircraft handling standard operating procedures. This included a requirement that the function was not to be engaged while the helicopter was descending.

Safety message

Pilots must be aware of the human factors hazards associated with loss of visual references. Pilots can protect themselves by maintaining the use of instrument scans in approaches at night, and making use of monitoring by trained and available crewmembers.

Flight planning should include assessment of the risk of a degraded visual environment. Operators should document their minimum acceptable levels of illumination and levels of tolerable risk. Where the risk exists, predetermined responses should be readily available.

Instrument flight rules (IFR) pilots in IFR-rated aircraft should prioritise use of inadvertent instrument meteorological conditions drills and pre-planned exit routes over recovery of visual meteorological conditions.

Flight crew and engineering teams should not rely solely on indicators, or absence of indicators, to determine airworthiness. If there is any reason to suspect exceedance of aircraft limits, operators should run diagnostics to determine the airworthiness of the aircraft beyond doubt.

People have a responsibility to aid their own rescue. Up-to-date registration of an EPRIB, and correct use of an EBIRB and other signalling equipment, simplifies a rescue of people in need. Australian Maritime Safety Authority guidelines exist to help people prepare for onshore and offshore remote area travel.

Download Final report
[Download  PDF: 2.43MB]

The occurrence


Safety analysis


Sources and submissions

Appendix A: Flight data

General details
Date: 13 May 2018   Investigation status: Completed  
Time: 21:10 CST   Investigation level: Defined - click for an explanation of investigation levels  
Location   (show map): 38 km ENE Darwin   Investigation phase: Final report: Dissemination  
State: Northern Territory   Occurrence type: Loss of control  
Release date: 16 April 2020   Occurrence category: Serious Incident  
Report status: Final   Highest injury level: None  

Aircraft details

Aircraft details
Aircraft manufacturer Leonardo Helicopters  
Aircraft model AW139  
Aircraft registration VH-YHF  
Serial number 31108  
Operator Careflight  
Type of operation Aerial Work  
Sector Helicopter  
Damage to aircraft Nil  
Departure point Darwin, Northern Territory  
Destination Darwin, Northern Territory  
Last update 16 April 2020