The pilot had flown the Cessna 172 aircraft, registered VH-DBG,
from Derby to Fitzroy Crossing earlier in the day. The pilot
reported that, prior to departure from Derby, he had dipped the
tanks using a dipstick, which displayed that there was 100 litres
of fuel on board. After arrival at Fitzroy Crossing, the pilot
added 44 litres of fuel to the aircraft. The pilot reported that he
again used the dipstick to check the amount of fuel. He said that
the dipstick displayed that there was 100 litres of fuel on board
the aircraft.
The aircraft departed from Fitzroy Crossing and the pilot
conducted a scenic flight on the return leg to Derby. As the
aircraft was approaching Derby, cruising at 3000 ft, the engine
began to splutter and then lost power. The pilot turned the
aircraft towards a sealed road and, after transmitting a PAN call,
conducted a forced landing onto a road. There were no reported
injuries. The pilot reported that the flight time for the return
flight was 1.8 hours. He also reported that he had leaned the
mixture during the cruise portions of the flight in accordance with
the engine manufacturer's operating manual. The ATSB did not attend
the site, however the investigation was conducted with reference to
information provided by the pilot in command, the operator and
several other parties.
The pilot arranged for a licensed aircraft maintenance engineer
to attend the aircraft on the road. The engineer reported that when
he arrived at the aircraft and checked the fuel tanks, there was no
useable fuel in either of the tanks. The pilot also reported that
there was no useable fuel remaining in the fuel tanks. The engineer
then checked the aircraft engine and fuel system and, after adding
fuel, the aircraft was flown back to Derby with no reported
problems.
Once the aircraft was back at Derby, further checks of the
aircraft and its systems were conducted, with no reported defects
found. The engineer reported that he added approximately 60 litres
of fuel to each tank in 30 litre increments and found that the
cockpit fuel gauges were showing quantities that were consistent
with the fuel calibration card that was present in the cockpit.
A post occurrence flight plan of the proposed flight, in
accordance with the company operations manual, revealed that the
aircraft was required to carry 104 litres of fuel. With this amount
of fuel onboard the aircraft, and a normal inflight fuel burn,
there would have been 43 litres of fuel remaining in the aircraft
at the point where the engine stopped.
The operator conducted an investigation into the circumstances
of the occurrence. The operator's investigation found that the
dipstick used by the pilot in command to check the fuel quantity
incorrectly indicated unusable fuel as useable fuel. The amount of
unusable fuel totalled 23 litres.
