Departure and Power Loss
During departure, while operating at about 500 ft to avoid low-level cloud, the aircraft's power level reduced below idle. The low altitude left the pilot with limited options for selecting a forced landing area. The landing was conducted with a downwind component in a paddock with obstacles, resulting in substantial aircraft damage.
Investigation Findings
The Australian Transport Safety Bureau (ATSB) investigation found a significant quantity of water in the aircraft's fuel system components after the accident. No other engine defects were identified, leading the ATSB to conclude that the engine power loss was probably due to water contamination.
Water was detected in the chemical hopper during an inspection the day before the accident, indicating that water could enter the hopper despite the seal and lip. This was considered a possible source of water contamination to the fuel system. However, the ferry fuel system was reportedly not used during the accident flight, so no obvious mechanism for contamination to enter the aircraft's fuel system was identified. It is also possible that water entered the wing tanks while the aircraft was exposed to rain in the days preceding the accident, as the fuel tanks were only partially filled.
Fuel Testing and Water Suspension
The methods used to check for water in the fuel—opaque sampling containers and fuel sight and smell—did not comply with Civil Aviation Safety Authority and United States Federal Aviation Authority guidance for pre-flight fuel testing. These methods did not ensure there were no suspended water droplets, a particular risk with turbine fuel, nor did they confirm that the fuel drain conducted on the morning of the flight was free of water.
Given the time between refuelling and the accident flight, any suspended water may have separated overnight as the fuel cooled. The change in aircraft attitude during departure and level off could have allowed water to move to the fuel pick-up in the tanks, resulting in power loss. However, engine data showed no surge when power was lost, which could indicate that water droplets remained in suspension and prevented the engine from producing enough power. By the time of the engine inspection, any suspended water would have separated out.
Additional Contamination
Examination of the fuel control unit revealed additional contamination and grease washout, which may have hindered fuel flow to the engine. However, insufficient information was available to determine if this occurred.
Unapproved Modification
The use of the chemical hopper as a ferry tank was contrary to the manufacturer's advice, and no approved technical data for the modification was available. Using approved engineering processes for modifications to safety-critical systems is important to ensure compliance with airworthiness standards.