Aviation safety investigations & reports

Loss of main rotor drive Robinson HelicopterR44, VH-ZWC, 83 km E of Darwin Airport, NT on 28 July 2011

Investigation number:
Status: Completed
Investigation completed

Safety summary

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What happened

On 28 July 2011, at around 1615 Central Standard Time, a Robinson R44 Raven II helicopter, registered VH-ZWC, departed Darwin Airport on a charter flight to Bamurru Plains, Northern Territory. Approximately 30 minutes into the flight, the aircraft lost main rotor drive and the pilot conducted an autorotative descent and landing. There were no reported injuries.

What the ATSB found

The ATSB’s investigation found that the loss of main rotor drive was associated with corrosion and subsequent fatigue failure of the main rotor gearbox gear carrier, as a result of water present in the main rotor gearbox.

What has been done as a result

The helicopter manufacturer has modified the design of the gear carrier to incorporate a metallic cadmium surface plating to improve the corrosion resistance of the assembly.

In May 2012, the Civil Aviation Safety Authority (CASA) released Airworthiness Bulletin 63-008, to raise awareness among operators and maintenance providers of Robinson R44 helicopters of the hazards associated with gearbox internal corrosion due to water ingress. The bulletin made several recommendations aimed at reducing the associated risks.

Safety message

Operators and maintainers of Robinson R44 helicopters are alerted to the potential for the ingress of water into the main rotor gearbox, and for the subsequent corrosion and possible fatigue cracking of componentry, which could lead to a loss of main rotor drive while in flight. Responsible persons are referred to the recommendations contained within CASA AWB 63-008, which are aimed at limiting the likelihood of water ingress and provide guidance on remedial action should water ingress be suspected.


Download Final Report
[Download  PDF: 2.58MB]
Alternate: [Download  DOC: 7.5MB]

Safety Issue

Go to AO-2011-088-SI-01 -

Ineffective corrosion protection of Main Rotor Gearbox

Paint application to the main rotor gearbox, gear carrier did not effectively protect the part from corrosion resulting from gearbox water ingress.

Safety issue details
Issue number: AO-2011-088-SI-01
Who it affects: Operators of Robinson R44 helicopters
Status: Closed – Adequately addressed
General details
Date: 28 July 2011   Investigation status: Completed  
Time: 1645 CST   Investigation level: Systemic - click for an explanation of investigation levels  
Location   (show map): Mary River floodplain, 83 Km east of Darwin    
State: Northern Territory   Occurrence type: Loss of control  
Release date: 27 August 2012   Occurrence category: Accident  
Report status: Final   Highest injury level: None  

Aircraft details

Aircraft details
Aircraft manufacturer Robinson Helicopter Co  
Aircraft model R44 II  
Aircraft registration VH-ZWC  
Serial number 11753  
Type of operation Charter  
Sector Helicopter  
Damage to aircraft Serious  
Departure point Darwin, NT  
Destination Bamurra Plains, NT  
Last update 03 April 2020