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On 4 August 2005, a Piper PA-31-350 Chieftain aircraft, registration VH-MZM, departed Dubbo Airport, NSW, for a local post-maintenance acceptance flight following an engine change. Shortly after departure, the pilot reported that the right engine manifold pressure fluctuated then dropped and maintained 28 inHg. The aircraft was returned to Dubbo with reduced power to the right engine.

Examination of the aircraft by the overhaul engineers revealed the newly-installed turbocharger turbine wheel had failed. The turbocharger was supplied to the ATSB for further examination and analysis.

During the course of the investigation, a second, similar turbine wheel failure occurred in a Piper PA-31-350, registration VH-TZY. Similarly to the first incident, the pilot observed significant manifold pressure fluctuations during cruise flight of the aircraft and the right engine was shut down. The aircraft was returned to the departure aerodrome. The turbocharger had been in service for approximately 241 hours and was subsequently forwarded to the ATSB.

Analysis of both turbine wheels revealed fracture characteristics indicative of a fatigue cracking mechanism. The failures had both occurred through a sealing ring groove, adjacent to the friction-welded joint between the turbine wheel and shaft components. While the post-failure damage of the fracture surfaces in both instances prevented the identification of the prime factor/s giving rise to the initiation of fatigue cracking, it was likely that the stress-raising effect of the ring groove location, geometry and associated microstructure, when combined with pre-existing cyclic loading conditions, was sufficient to initiate fatigue cracking and consequent turbine wheel failure.

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[ Download PDF: 604KB]
General details
Date: 15 March 2006 Investigation status: Completed 
Location:Dubbo, Aerodrome Investigation type: Occurrence Investigation 
State: New South Wales Occurrence type: Engine failure or malfunction 
Release date: 26 June 2007 Occurrence class: Technical 
Report status: Final Occurrence category: Incident 
 Highest injury level: None 
Aircraft details
Aircraft model: PA-31-350 
Aircraft registration: VH-MZM 
Serial number: 31-8152187 
Type of operation: Aerial Work 
Damage to aircraft: Nil 
Departure point:Dubbo, NSW
Destination:Dubbo, NSW
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Last update 18 April 2018