The ATSB's final investigation report into a Piper Chieftain accident near Condobolin, NSW on 2 December 2005, resulting in four deceased persons, confirms that the aircraft broke up during flight when its structural limits were exceeded in the vicinity of thunderstorms.

The Australian Transport Safety Bureau report states that there was no indication, either by way of emergency radio transmission from the pilot, or in a change in the altitude, track and speed of the aircraft as recorded by radar, that the flight was not proceeding normally. Some minutes after the pilot reported diverting left of track to avoid weather, communications with the aircraft were lost.

The absence of an on-board recording device on the aircraft prevented a full analysis of the circumstances of the breakup. However, while post-impact fire damage limited the extent to which some of the aircraft's system's, including the fuel and electrical systems, could be examined, wreckage examination did not reveal any pre-existing fault or condition that could have weakened the aircraft structure and caused it to break up at a load within the design load limit.

A line of severe thunderstorms crossed the aircraft's planned track and were the subject of a SIGMET (significant weather advice) issued by the Bureau of Meteorology. As the SIGMET information did not meet the criteria for direct notification, it was not advised directly to the pilot of the aircraft. The investigation was unable to determine if the pilot had obtained the SIGMET from any of the range of pre and in-flight weather briefing services available to the pilot.

Analysis of the prevailing weather indicated that, immediately before the accident, the aircraft was likely to have been surrounded to the east, west, and south by a large complex of thunderstorms. That situation may have limited the options available to the pilot to avoid any possible hazardous phenomena associated with the storms.

Although, as a result of a review of Flight Information Service initiated in November 2004, Airservices Australia had identified inconsistencies and ambiguities in the provision of Flight Information Service, including Hazard Alert procedures, they were not assessed by the investigation to be contributing factors to the accident. As a result of its review, Airservices Australia initiated changes to the Flight Information Service and Hazard Alerts sections of the Manual of Air Traffic Services and the Aeronautical Information Publication to improve future safety.

While not contributory to the accident, the report identifies a number of inconsistencies between Australian SIGMET issemination procedures and those contained in International Civil Aviation Organization (ICAO) documentation. The report contains recommendations to Airservices Australia and the Civil Aviation Safety Authority to review Australian procedures with a view to minimising those inconsistencies.

The circumstances of the accident are a salient reminder to pilots of their responsibilities to request weather and other formation necessary to make safe and timely operational decisions, and of the importance of avoiding thunderstorms by large margins.

Copies of the report can be downloaded from the ATSB's internet site at www.atsb.gov.au.

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