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The Australian Transport Safety Bureau did not conduct an on-scene investigation of this occurrence.

 

FACTUAL INFORMATION

On 15 June 2004, a Hiller Aviation UH-12E helicopter, registered VH-HMT, crashed during an agricultural operation, after the pilot reported a loss of tail rotor authority. The pilot was not injured in the accident. The horizontal stabilizer was found about 150 m from the wreckage site, indicating that it had separated from the helicopter in-flight. The operator reported that damage to the stabiliser and the tail rotor blades was consistent with the separated stabiliser coming into contact with the tail rotor blades, as it was still connected to the helicopter by the tail light wiring. The operator reported that an engineering examination found no evidence of tail rotor system failure.

The horizontal stabiliser spar tube failed in the area where the tube passes through a collar in the doubler attached to the inner stabiliser rib (refer to figure 1).

Figure 1: Horizontal stabiliser and detail of the spar tube and doubler.
Horizontal stabiliser and detail of the spar tube and doubler.

Helicopter

The helicopter was manufactured in 1978 and had accumulated 6,903.50 hours time in service at the time of the accident. In September 2002, at 6,386.25 hours in service, it sustained major damage following a sudden main rotor stoppage. The helicopter was rebuilt and had since accumulated approximately 517.20 hours in service. It was maintained in accordance with the maintenance requirements applicable at the time and had a valid Maintenance Release. It had flown approximately 31 hours since the last periodic inspection, a 100 hourly inspection completed in May 2004.

Horizontal stabiliser

The operator advised the Australian Transport Safety Bureau (ATSB) that the horizontal stabiliser is not a serial numbered item and its time in service since new was not known. The stabiliser was fitted to the helicopter when it was acquired from its previous owner. During the helicopter rebuild in September 2002, the stabiliser was inspected in accordance with the 100 hourly component inspection guide and the Hiller UH-12E maintenance manual, before being re-installed. The component inspection guide required the stabiliser tube to be inspected for corrosion and security and the maintenance manual detailed the spar tube inspection requirements and wear limits. No anomalies with the horizontal stabiliser were reported at that time.

Spar tube failure

The failed horizontal stabiliser was forwarded to the ATSB for detailed examination. That examination revealed that the stabiliser spar tube fractured as a result of fatigue cracking. The crack initiation occurred at a number of locations where the tubing had been reduced in wall thickness by wear. It was apparent that the wear of the tubing was associated with small scale repeated movement between the stabiliser tube and the doubler attached to the stabiliser's inner rib. There was no evidence of any pre-existing defect present.

A search of the ATSB, United States National Transportation Safety Board and Federal Aviation Administration databases found no reported events involving an in-flight separation of the horizontal stabiliser on similar helicopter types.

 

As a result of this occurrence, The Australian Transport Safety Bureau (ATSB) draws to the attention of Australian operators of Hiller UH-12E helicopters, the difficulties associated with inspecting the horizontal stabiliser spar tube assembly.

The ATSB has also advised the Civil Aviation Safety Authority of the difficulties associated with inspection of the horizontal stabiliser spar tube assembly and will circulate copies of this report to all Australian operators of Hiller UH-12E helicopters.

 
General details
Date: 15 June 2004 Investigation status: Completed 
Time: 1425 hours EST Investigation type: Occurrence Investigation 
Location   (show map):11 km W Innisfail Occurrence type:Collision with terrain 
State: Queensland Occurrence class: Operational 
Release date: 09 August 2005 Occurrence category: Accident 
Report status: Final Highest injury level: None 
 
Aircraft details
Aircraft manufacturer: Hiller Aviation 
Aircraft model: UH-12 
Aircraft registration: VH-HMT 
Serial number: HA3066 
Type of operation: Aerial Work 
Damage to aircraft: Substantial 
Departure point:Innisfail Quarry, QLD
Departure time:1421 hours EST
Destination:Innisfail Quarry, QLD
 
 
 
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Last update 13 May 2014