A Bell 47J helicopter was being ferried by two pilots from
Lyndock SA to Kings Creek Station NT over a period of 3 days.
Refuelling stops were planned for Port Augusta, Roxby Downs, Coober
Pedy, Cadney Park if required, and Kulgera. Additional equipment
was also carried, including a ground refuelling hose and pump unit,
aircraft manuals, hand tools, additional engine oil, water, and
seven 20 L jerry cans of fuel.
The flight was uneventful to Cooper Pedy where a flight plan was
lodged nominating Cadney Park and Kulgera as landing points. The
helicopter subsequently departed at about 0730. When it failed to
arrive at Cadney Park or Kulgera, a search was initiated. The
burnt-out wreckage of the helicopter was located 2 days later in
flat, open, sparsely timbered country, about 1 NM south-west of
Temptation Bore and approximately 152 NM from Coober Pedy, close to
the direct track to Kulgera. The accident was not survivable.
At the time of the accident the weather was fine and clear, with
a light breeze from the south-east, and a temperature in the
vicinity of 30 degrees Celsius.
Examination of the wreckage did not reveal any pre-existing
defects which may have contributed to the accident. An intense
post-impact fire fuelled by the fuel from the jerry cans had
consumed the cockpit and forward section of the tail boom. The
engine displayed severe impact and external fire damage, but all
internal components were intact, well lubricated, and capable of
normal operation. The fire had destroyed the fixed emergency
locator transmitter mounted on a bracket at the forward section of
the tail boom. The remains of a hand-held emergency locator beacon
were found in the debris of the burnt cockpit. The damage sustained
by the main and tail rotor assemblies was consistent with the
transmission system not being powered at the time of impact. The
rotational velocity of the main and tail rotor assemblies was very
low at impact and it was likely that the main rotor RPM was too low
for a controlled descent. Damage sustained by the engine cooling
fan indicated it was not rotating at impact. Some of the flight
control systems had been consumed by the fire, but the remainder
were correctly connected and functioned normally. The pilot's
collective lever and cyclic control stick had separated during the
impact. Both displayed bending overload failures but no fire damage
was evident.
One main fuel tank had collided with a main rotor blade during
the impact sequence. That tank was ruptured and deformed from
collision with the blade, and contained a minute quantity of fuel,
but displayed no evidence of fire damage. The other main fuel tank
was ruptured and heavily sooted externally, but contained no fuel,
and there was no evidence of fire internally. The remainder of the
fuel system was too extensively damaged to determine if a fuel leak
had existed during flight. Of the seven jerry cans, most were
ruptured and heavily sooted externally. Fire and explosives
experts' analyses determined that the main tanks contained only a
small quantity of unusable fuel at impact. The intensity of the
fire indicated that there was a substantial quantity of fuel in the
jerry cans. Earth displaced from the impact craters made by the
forward cockpit section and tailskid was consistent with the
helicopter being in a nose-down attitude, with some forward
velocity at impact.
Maintenance records for the helicopter indicated that it had
been correctly maintained in accordance with an approved system of
maintenance. The maintenance release was current, and there were no
outstanding maintenance requirements.
Both pilots were appropriately licensed for the flight. The
pilot flying at the time of the accident had about 350 hours of
rotary wing flight time, but had limited experience on the Bell 47J
type. The pilot in the rear seat had over 7,000 hours rotary wing
flight time, but his logbook indicated that he had not operated the
Bell 47 type since before September 1997.
The estimated weight and balance of the helicopter on departure
from Coober Pedy indicated that the centre of gravity was within
approved limits and its weight was within the authorised maximum
take-off weight.
The investigation determined that the main fuel tanks of the
helicopter and the seven additional 20 L jerry cans were full when
it departed Lyndock. The fuel management between Lyndock and the
final refuelling at Coober Pedy could not be determined. After
refuelling at Coober Pedy on the evening before the accident
flight, the helicopter was hover taxied to another area for
overnight parking. The main tanks were therefore less than full at
departure from Coober Pedy the next morning. The range of the
helicopter with full main tanks was insufficient to reach Kulgera
and it would have had to land en route to be refuelled from the
jerry cans in order to reach its destination.
It was reported that the pilot in the rear seat had flown the
route several times and was known to refuel at locations of high
visibility. He had refuelled at Aston Hill, about 15 NM
north-north-west of Cadney Park on previous occasions but there was
no evidence to suggest that the helicopter had landed between
Coober Pedy and the accident site on this occasion.
Calculations using the known fuel quantities purchased at the
previous enroute refuelling stops, indicated that the range of the
helicopter with full main tanks should have been sufficient to
reach Temptation Bore. The pilot may have been planning to land and
refuel at Temptation Bore, which would have been visible in the
near distance when the engine stopped from fuel exhaustion. The
reason the engine stopped from fuel exhaustion and why the
helicopter then collided heavily with the ground in a nose low
attitude, with the rotor system rotating well below the speed
required for a controlled descent, could not be determined.