The ATSB has reported substantial safety action to seek to ensure off-course 'RAM' alerts are routinely passed by air traffic controllers to pilots in future to help avoid a repeat of the fatal accident near Benalla in 2004 that claimed the lives of all six people on board. The ATSB has also urged pilots not to rely on a single source of navigation information and to pay careful attention to the use of automated flight systems.

However, the Australian Transport Safety Bureau in its Final Investigation Report was unable to find why the pilot descended a Piper Cheyenne aircraft into terrain when nearly 30km off-course. Cloud obscured terrain that could have alerted the wrong top-of-descent position.

The investigation was particularly difficult due to the destruction of evidence during the impact and post-impact fire and lack of flight recording devices. Extensive examination and testing of the recovered components from the aircraft's GPS system was conducted utilising the expertise of international safety agencies, including the French Bureau d'Enquetes et d'Analyses, the US National Transportation Safety Board, system component manufacturers and the Australian Defence Science and Technology Organisation. Unfortunately, despite these prolonged efforts, the reason for the tracking error could not be determined.

The aircraft was on a private flight from Bankstown to Benalla and did not follow the usual course taken by the pilot, but diverted south along the east coast before tracking directly to Benalla. During that part of the flight, the aircraft diverged between 3.5 and 4 degrees left of track, with the pilot apparently unaware of the tracking error. The aircraft was fitted with a Global Positioning System (GPS) navigation system and the flight was being monitored by Air Traffic Control until it left radar coverage near Benalla.

During the flight, the air traffic control system's Route Adherence Monitoring (RAM) system triggered alerts to indicate that the aircraft was deviating from its planned route, but controllers did not question the pilot about the aircraft's position. The investigation found that the instructions to controllers relating to RAM alerts were ambiguous and that the sector controller involved wrongly assumed that the pilot was tracking to another waypoint.

The pilot reportedly often disabled the radio altimeter during a flight. That equipment may have indicated the aircraft's unsafe proximity to terrain in time to prevent the controlled flight into terrain accident (CFIT) if it had been operating.

In addition to the extensive safety action by Airservices Australia to seek to avoid a repeat of the accident, the ATSB has issued a safety recommendation to the Civil Aviation Safety Authority to review the requirements for the carriage of on-board recording devices in Australian registered aircraft which could assist investigators establish the reasons for any accidents that may occur in the future.

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