Since the release by the ATSB on 19 December 2001 of Report 200002157 on the fatal accident involving Piper Chieftain VH-MZK in Spencer Gulf in South Australia on 31 May 2000, further events have taken place, and additional information has become available, regarding issues that were examined in ATSB Report 200002157. The ATSB formally re-opened its investigation in November 2002 under the provisions of Part 2A of the Air Navigation Act in order to test the significance of the new evidence.
From July 2002 until July 2003, the South Australian Coroner conducted a public inquest into the accident. The Coroner delivered his findings on 24 July 2003 and disagreed with the conclusions in ATSB Report 200002157 and was critical of the ATSB investigation. The Coroner concluded that the left and right engines had failed independently. He found that the right engine overheated and was damaged during the climb from Adelaide, and developed a hole in the No 6 piston 8 minutes into the cruise phase of the flight. He concluded that the left engine subsequently independently failed because of fatigue cracking initiated by a sub-surface manufacturing defect in the crankshaft.
Between 1 February and 16 September 2002 (after ATSB Report 200002157 was released), the engine manufacturer issued Mandatory Service Bulletins 550, 552, and 553 concerning potential crankshaft defects. The serial number of the MZK left engine crankshaft appeared in Service Bulletin 553. It has been reported that of the crankshafts that were subject to that service bulletin, almost 70 percent of those tested were not defective and were permitted to continue in service after testing.
As stated in ATSB Report 200002157, initial examination of the crankshaft by the ATSB indicated that it complied with the proprietary standards set by the engine manufacturer. Based on their examination of a sample that had been cut from the crankshaft by the ATSB and stored for 18 months, academics from a local university commissioned by the Coroner, along with a US firm acting for the plaintiffs in civil damages litigation, reported the existence of 'massive' high temperature oxide 'inclusions' in the crankshaft material. However, later examination by the same experts and destructive testing of the crankshaft in the vicinity of the fatigue crack origin did not reveal any evidence of massive inclusions. Nevertheless, the opinion of the US firm concluded that a manufacturing defect (rather than a thermal crack as suggested in ATSB Report 200002157) was responsible for initiating the fatigue crack. They stated that while no large foreign body manufacturing inclusion was found at the crack initiation site, it may have 'fallen out' as the crack propagated. Detailed examination of the crankshaft material and the fracture area, including both sides of the fracture surface by the ATSB (in the presence of independent observers) in March 2003 did not reveal any irregularity in the crankshaft steel that could have initiated the fatigue fracture under normal engine operating conditions. No evidence of any large inclusions or of any 'honeycomb feature' as suggested in material associated with the service bulletins was found. Without receiving expert advice, the Coroner in his findings stated that the ATSB's 50 page test report 'takes the matter no further' and chose to rely on earlier opinion and circumstantial evidence.
The ATSB does not agree with the Coroner's findings and is strongly of the view that the engine failure mechanisms and the sequence of events contained in ATSB Report 200002157 remain the most likely explanation of the circumstances of the accident, based on the limited factual information that was available. This Supplementary Aviation Safety Investigation Report includes the ATSB's detailed response to the Coroner's findings. The report also includes further explanation of the main issues addressed in ATSB Report 200002157, as well as matters of major interest that arose during the inquest, including:
- The possibility that the failure of the VH-MZK left engine crankshaft was linked to a manufacturing defect,
- The possibility of an engine failure sequence that differed from that advanced in Report 200002157,
- The extent and timing of the left engine No 6 connecting rod big end bearing 'failure',
- The operation of the turbocharger on the Textron Lycoming TIO-540 engine,
- The maximum single engine speed the aircraft could achieve.
In summary, the ATSB explanation for the initiation of the fatigue crack in the left engine crankshaft about 50 flights before the accident was a thermal crack caused by localised surface heating when a bearing insert failed to operate as designed and a bearing edge interfered with the crankshaft surface. This resulted from some combination of excessive engine pressures probably caused by preignition from incandescent lead oxybromide deposits (linked to fuel leaning, eg in the climb but within the aircraft manufacturer's guidelines) and bearing slippage assisted by an anti-galling lubricant. In addition to MZK, this was based on the ATSB's observations of damage in a number of engines (now more than a dozen) including two from another engine manufacturer. The ATSB concluded that the holing of the right engine No. 6 piston was the result of detonation in response to the left engine failure (the right engine damage was therefore a dependent failure). As the ATSB stated when releasing Report 200002157 on 19 December 2001, it is not appropriate to 'blame' the young pilot in this scenario given the paucity of evidence and the ATSB did not do so.
The ATSB does not agree with the Coroner that MZK's pilot was likely to have allowed, ahead of any stressful situation, his right engine to overheat to a point 8 minutes into the cruise of melting a hole in a piston (especially as the temperature probe is atop the melted No. 6 piston cylinder) and then be unlucky enough that a deep-seated long-term progressive fatigue crack problem in the left engine crankshaft would have suddenly caused that engine to independently fail.
Following the release of ATSB Report 200002157, the ATSB received responses from the US FAA concerning Recommendations R20010254 and R20010255 that dealt with combustion chamber deposits and anti-galling compounds. The FAA advised that it would review the effect of anti-galling compounds on bearing insert retention, and that it was conducting an extensive evaluation of the detonation characteristics of high performance reciprocating engines and would include an examination of deposit formation as part of that evaluation.
In July 2002, the ATSB issued Safety Recommendation R200220149 for CASA to examine the potential safety benefits of devices that monitor aircraft fuel and engine system operation and whether those systems should be fitted to general aviation aircraft engaged in air transport operations. CASA advised that it did not consider the safety benefits of those devices warranted their fitment being made mandatory. However, CASA did not have any concern with operators voluntarily fitting such equipment.
While maintaining that the engine failure mechanisms and the sequence of events contained in ATSB Report 200002157 remain the most likely scenario, the Bureau examined carefully a range of scenarios. In particular, an assessment was made of any safety action that might be required if an accident as a result of a less likely scenario was to be prevented in the future.
The Coroner included five recommendations in his findings:
- As suggested in the ATSB's submissions, the Coroner sought clarification of engine operating procedures between different versions of pilot operating handbooks and flight manuals for piper Chieftain aircraft to ensure that engine detonation limits are not exceeded. The ATSB has written to CASA supporting the Coroner's recommendation and requesting that CASA seek clarification of detonation limits from the US FAA, and examine how engine operating procedures for operators of more than one model of a particular aircraft type take proper account of differences in versions of operating manuals and handbooks.
- The Coroner sought improved lines of communication between international aviation regulation and safety investigation agencies, even where litigation might be threatened. The ATSB already enjoys close working international relationships, but agrees that the flow of information could be improved in some instances. However, there are practical limitations that apply in other countries and through multilateral agencies over which the ATSB has no control.
- The Coroner sought that CASA mandate the fitment of on-board recorders in aircraft carrying fare-paying passengers. The ATSB considers that its Safety Recommendation R200220149, referred to above, addressed that issue.
- The Coroner sought the carriage of life jackets and/or life rafts in fare-paying passenger operations over water, which is supportive of earlier ATSB recommendations. ATSB Report 200002157, Section 4.4, detailed Safety Recommendations R20000248 and R20000249 concerning the carriage of life jackets and emergency and life saving equipment. R20000248 was accepted by CASA and Civil Aviation Order 20.11 amended to require life jackets to be carried on all passenger flights over water. As regards R20000249, CASA has advised that it was considering a number of issues regarding emergency and life saving equipment in twin engine aeroplanes in the context of the proposed CASR Part 121B, Air Transport Operations - Small Aeroplanes. The draft regulations included in a Notice of Proposed Rule Making (NPRM) released by CASA in July 2003 for this Part includes various requirements for emergency cabin lighting and carriage of items such as of life jackets and other flotation devices, life rafts, ELTs (Emergency Locator Transmitters) or EPIRBs (Electronic Position Indicating Radio Beacons) and other survival equipment, including provisions.
- The Coroner proposed a research program concerning self-deploying ELT units. The ATSB's recommendation to CASA R20000249 encompasses enhanced emergency and life saving equipment such as ELTs and the Bureau believes that CASA, AusSAR (AMSA) and Defence are best placed to progress the issue.
|Date:||31 May 2000||Investigation status:||Completed|
|Time:||1905 hours CST|
|Location:||28 km SE Whyalla Airport|
|Release date:||28 October 2003||Occurrence class:||Mechanical|
|Report status:||Final||Occurrence category:||Accident|
|Highest injury level:||Fatal|
|Damage to aircraft||Destroyed|
|Departure point||Adelaide, SA|
|Departure time||1823 hours CST|
|Role||Class of licence||Hours on type||Hours total|