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The aircraft was being ferried to a strip in the Hunter Valley to carry out parachute dropping. En-route, although performance appeared normal, the pilot sensed a possible problem with the turbine engine and landed at Somersby NSW. After landing, a visual inspection of the engine was undertaken and several ground runs carried out, without any defect being found. The pilot elected to return to Camden where further checks could be made. The aircraft took off towards the south and climbed to a height of about 1000 feet, at which point the pilot heard a bang from the engine compartment which was followed soon after by a very loud bang associated with noises described by the pilot as like "forcing a crowbar into the engine".

During the ensuing forced landing in fine, calm conditions, the pilot misjudged the final stage of the landing approach, resulting in the aircraft landing very heavily and sustaining considerable damage. A subsequent engineering investigation found the engine had suffered a catastrophic malfunction resulting from fatigue failure of a helical thrust washer from the high speed pinion assembly. The fatigue crack growth resulted from applied alternating loads, probably due to excessive wear of the helical gear shaft bearing. About one week prior to the flight, engine oil sample and filter element had been removed in accordance with Airworthiness Directive AD/TPE 331/9.

Although the samples had not been immediately sent for laboratory analysis, the owner was allowed to operate the engine for a further 50 hrs before satisfactory test results were received. When the samples were examined during the investigation, articles were found which indicated bearing deterioration prior to the engine failure. Earlier in the year, the aircraft had sustained a propeller ground strike, resulting in the engine being removed and returned to an overhaul facility for inspection. It has been reported that when the engine was re-installed in the aircraft, a torque meter calibration check was not carried out in accordance with the procedures published in the manufacturer's maintenance manual. Although not positively established, the mode of engine failure was consistent with an excessive torque setting.

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General details
Date: 26 October 1990 Investigation status: Completed 
Time: 840  
Location:Somersby Investigation type: Occurrence Investigation 
State: New South Wales  
Release date: 16 December 1991  
Report status: Final Occurrence category: Accident 
 Highest injury level: Serious 
Aircraft details
Aircraft manufacturer: de Havilland Canada 
Aircraft model: DHC-2 
Aircraft registration: VH-AAX 
Serial number: 1411 
Type of operation: Private 
Damage to aircraft: Substantial 
Departure point:Somersby NSW
Departure time:838
Destination:Camden NSW
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