On 29 September 2011 at 1240 Central Standard Time, a Gippsland Aeronautics GA-8 Airvan, registered VH-AJZ, departed Marree, South Australia with one pilot and six passengers for a scenic charter flight over Lake Eyre and surrounding regions. About 45 minutes after takeoff and while flying at a height of about 500 ft above ground level the pilot felt a shudder through the airframe, then heard a loud pop and the propeller stopped. The pilot carried out a successful forced landing on the Birdsville Track, approximately 135 km north-north-east of Marree.
What the ATSB found
The No. 5 piston of the aircraft’s single engine sustained a fatigue failure, resulting in severe mechanical damage that stopped the engine. The engine’s oil system was contaminated by metal chipping (spalling) from the bodies of two tappets because of contact fatigue to the tappets. This increased the risk of abnormal wear and failure of pistons and other engine components. The ATSB could not conclusively establish that this led to the piston failure, although similar failures in comparable engines had been attributed to that mechanism.
Although there was little warning to the pilot during flight of the impending engine failure, the operator had recently noted an abnormally high consumption of engine oil, which could have indicated poor engine condition. The oil consumption in fact exceeded the manufacturer’s limits for continued operation, but was misinterpreted, when referred to the maintenance organisation, as falling within those limits.
Finally, there was severe spline wear on the engine-driven fuel pump (EDFP) drive which could, if undetected, have led to EDFP drive failure and sudden loss of fuel flow to the engine, although this did not contribute to the occurrence.
What has been done as a result
The engine manufacturer had previously introduced a factory-fitted roller tappet to reduce spalling. Subsequently, for engines not yet incorporating that modification, the manufacturer introduced a flat tappet with an improved bonded coating, providing a more resilient sliding surface.
The aircraft operator reviewed the circumstances of this occurrence and has improved their monitoring of engine operating data, including oil consumption.
Accelerated and abnormal EDFP spline wear in this engine type has been subject to ongoing study by the Civil Aviation Safety Authority (CASA). A number of failed EDFP shafts were examined by the ATSB in support of the CASA study.
The investigation highlights the importance of operators monitoring and using engine oil consumption data as a diagnostic tool and of immediately investigating oil consumption figures that fall outside the manufacturer’s acceptable limits. Also highlighted are the importance of the engine manufacturer’s recommended oil filter inspections during scheduled maintenance and the associated guidance material when assessing any debris or contamination found.
|Date:||29 September 2011||Investigation status:||Completed|
|Time:||1335 EST||Investigation level:||Complex - click for an explanation of investigation levels|
|Location:||Birdsville Track - 135 km NNE of Marree|
|State:||South Australia||Occurrence type:||Engine failure or malfunction|
|Release date:||18 March 2013||Occurrence category:||Serious Incident|
|Report status:||Final||Highest injury level:||None|
|Aircraft manufacturer||Gippsland Aeronautics Pty Ltd|
|Type of operation||Charter|
|Damage to aircraft||Unknown|
|Departure point||Marree, SA|