The Hughes 369HS helicopter was on a ferry flight from Western Australia to New South Wales. After landing at Ceduna to refuel, the pilot was advised by the local fuel agent that the Jet A1 fuel bowser was non-operable. The pilot reported that the operator's maintenance organisation advised him that the helicopter could be flown using avgas as an alternative fuel. The pilot reported that after the refuel, he completed a pre-flight inspection, started the helicopter and ran it for a short time before taking off. After takeoff, he conducted a circuit to ensure that the engine was performing correctly. All the indications appeared normal so the pilot decided to depart the airfield. During the climb, at about 500 ft, the pilot turned off the fuel start pump switch. He reported that almost immediately after he turned the pump off, the engine failed. The pilot reported that he placed the helicopter into an auto-rotative descent, turned on the start pump and transmitted a Mayday that was acknowledged by flight service. The pilot also reported that although he noticed the engine-out warning system and the re-ignition systems operating during the descent, the engine did not relight. The helicopter's emergency locator beacon automatically operated following the firm auto-rotative landing. After landing, the pilot turned off the helicopter's fuel and electrical systems and vacated the cockpit. The helicopter was extensively damaged during the landing, but the pilot was not injured. The Bureau of Air Safety Investigation did not conduct an on-site investigation.
The version of the flight manual that was current when the accident occurred included a caution that stated, "When using alternate fuel mixtures or emergency fuels, the start pump should remain on until the engine is shutdown". Avgas has a higher vapour pressure than kerosene type fuel and is therefore susceptible to vapour lock in the vacuum type fuel system used in this helicopter. The pilot reported that the maintenance organisation did not advise him of the fuel pump requirement and that the caution did not appear in the flight manual available in the aircraft at the time. The helicopter's manufacturer reported that the amendment that included the caution relating to the use of the pump was issued in 1998. The operator was unable to provide a reason for the failure to incorporate the amendment relating to the use of alternative fuels in the helicopter's flight manual.
The investigation also found that the fuel filter element's outer fine mesh screen was substantially blocked with corrosion by-products from the stainless steel mesh filter element. Some of the screen pleats at the bottom of the filter element had cracked as a result of a corrosion-cracking mechanism. Analysis indicated that the corrosion of the fuel filter element was possibly caused by sulphur-bearing compounds found in Jet A1 fuel. It would be normally expected that such extensive blockage of the fuel filter would trigger the fuel filter caution light. However, the crack found in the filter element pleat may have been large enough to permit fuel to pass through and not create sufficient pressure differential within the fuel filter housing to trigger the caution light.
Following the refuel with avgas, the engine apparently lost power when the pilot turned off the fuel start pump. It is possible that when the fuel start pump was turned off, a vapour lock formed in the helicopter's fuel system, interrupting the fuel flow to the engine and causing the engine to flame out. The effect of the corroded and blocked fuel filter in contributing to the engine power loss was not determined.
|Date:||27 February 1999||Investigation status:||Completed|
|Time:||1352 hours CSuT|
|Location:||9 km E Ceduna, Aero|
|State:||South Australia||Occurrence type:||Forced/precautionary landing|
|Release date:||19 October 1999||Occurrence category:||Accident|
|Report status:||Final||Highest injury level:||None|
|Aircraft manufacturer||Hughes Helicopters|
|Type of operation||Aerial Work|
|Damage to aircraft||Substantial|
|Departure point||Ceduna, SA|
|Destination||Port Augusta, SA|
|Role||Class of licence||Hours on type||Hours total|