The pilot had planned a flight from Cairns to Mt Mulligan, a
distance of about 75 km, and return. Based on his flying experience
on the helicopter, he assumed a fuel usage rate of 65 litres per
hour. The helicopter was refuelled to full tanks (210 litres)
before departure. The planned time interval to Mt Mulligan was 38
minutes, based on a true airspeed of 70 kts and a groundspeed of 80
kts. The expected groundspeed for the return flight was 60 kts.
The helicopter departed Cairns at about 1420 and arrived at Mt
Mulligan 44 minutes later. The pilot then operated in the area for
about 20 minutes before landing. He visually assessed the fuel
contents as 136 litres before departing Mt Mulligan for Cairns at
about 1620 EST. He advised air traffic services flightwatch of a
SARTIME of 1730. The cruising altitude was 3,000 ft. During the
latter stages of the flight, when about 10 km west of Cairns, the
pilot amended the SARTIME to 1740. He also had to divert south
track because of cloud. At this time, the fuel contents gauge was
indicating about one quarter full. A few minutes later, when the
helicopter was about 3 km southwest of Cairns Airport, the engine
lost power. The pilot successfully completed an emergency landing
onto a suburban street.
Examination of the helicopter revealed that the fuel tanks
contained 4.8 litres of fuel. (The manufacturer's data indicated
that the unusable fuel quantity for the helicopter was about 8
litres.) After fuel was added to the tanks, the engine operated
normally. No fault was found with any other system that might have
caused the engine failure. Calculations indicated that the actual
fuel usage rate was about 77 litres per hour. This was in line with
data from the engine manufacturer that indicated a usage rate of
75-80 litres per hour for similar operations.
The pilot had not previously operated the helicopter on flights
longer than 30 minutes or at altitudes above 2,000 ft and did not
properly understand the relationship between operating altitude,
power settings, and fuel consumption. This lack of understanding,
combined with the fuel usage rate the pilot used in planning the
flight, resulted in the fuel supply to the engine being exhausted
before the flight reached its destination.
