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.