The Beech C24R Sierra aircraft had been flown to Trilby Station
as part of a weekend pleasure trip two days before the accident.
The three occupants, including the aircraft owner, were qualified
pilots experienced on the aircraft type.
The aircraft owner was the pilot in command for the flight from
Hoxton Park to Trilby Station. During their stay at the property,
none of the occupants of the aircraft had given any indication that
there had been any problems regarding the operation of the aircraft
on that flight.
For the return flight, the youngest of the three men was
designated as pilot in command. Witnesses indicated that he
occupied the front left seat of the aircraft. He was appropriately
licenced for the aircraft type and held a current medical
certificate. The aircraft owner occupied a rear seat while the
other pilot occupied the front right seat.
Witnesses reported that the engine was 'running roughly' and
'missing' shortly after startup. One witness recalled the pilot
carrying out a pre-takeoff engine run-up. The aircraft was then
observed to taxy to the end of the dirt strip where the pilot
immediately commenced the take-off run. Throughout the take-off
run, the aircraft appeared to accelerate slowly with reported
'frequent backfires' and the engine 'missing badly'. One witness
expected the pilot to reject the takeoff. None of the witnesses
observed the aircraft become airborne. Several seconds later the
engine noise ceased, followed by the sound of an impact. The
burning wreckage of the aircraft was subsequently located on the
western bank of the Darling River.
The Bureau of Meteorology assessed the weather conditions at
Trilby Station around the time of the accident as fine, with a
temperature of 18 degrees C, and the wind from the NW at 15 knots.
Calculations based on this data indicated that during the takeoff
there would have been approximately 5 knots headwind component, and
14 knots crosswind from the right. This was confirmed by witness
observations.
The airstrip was 1000 m long and 30 m wide, with a level, dry,
gravel surface. There were several small trees 108 m beyond the end
of the strip on the extended centreline and a cleared area to the
right.
The Pilot's Operating Handbook for the aircraft indicated that
with 15 degrees of flap selected, a maximum take-off weight of 2750
lbs, a 5 kt headwind, temperature of 18 degrees C, and 350 ft
elevation above mean sea level, the take-off distance to an
obstacle height of 15 m (50 ft) was predicted to be 503 m (1650
ft). The trees struck by the aircraft were 1108 m (3635 ft) from
the downwind end of the strip.
Autopsy and toxicological examinations of the pilot in command
did not reveal any pre-existing medical condition that would have
prevented him from safely operating the aircraft.
Inspection of the area between the end of the strip and the
accident site revealed that, after becoming airborne and while in a
left wing low attitude, the aircraft had struck the tops of several
small trees located beyond the end of the airstrip. The aircraft
then crossed the Darling River, impacting on the steeply sloping
western bank. Fire had destroyed most of the aircraft structure,
except the aircraft's empennage, engine and propeller, limiting the
amount of useful information available to the investigation.
Examination of the flap system indicated that the flaps were
positioned at approximately 15 degrees. The landing gear position
could not be determined. The airframe fuel system was destroyed in
the fire. Both fuel tank caps were located secured to their fuel
tank filler necks and the fuel selector position was not able to be
determined.
The propeller blades were found in a fine pitch position. Fire
damage to the propeller governor precluded an assessment being made
regarding its pre-impact serviceability. The nature of the damage
to the propeller blades indicated that they were not rotating under
power on impact. The severe heat damage to the engine's ignition
system and fuel control system prevented an assessment being made
of their pre-accident operation.
The engine and propeller were removed from the wreckage for a
technical examination at an appropriate overhaul facility. This
examination revealed spalling damage on the number-1 cylinder
exhaust valve camshaft follower. The number-1 cylinder inlet valve
stem tip was 'belled' out. The number-4 cylinder connecting rod
gudgeon pin bushing was a loose fit in the rod small end. However,
nothing significant was noted during the examination of the core
engine that would have prevented its operation.
The spark plugs fitted to the engine were part number REM38E in
all cylinder lower plug positions, and part number REM40E in all
upper positions. Due to the engine being found inverted at the
accident site, most of the spark plugs had been coated with engine
oil. When tested, all spark plugs operated normally, with the
exception of the number-4 cylinder lower plug. After it had been
cleaned, the spark plug again operated normally.
The engine manufacturer listed the spark plugs approved for use
in their various model engines, and advised that only the approved
plugs were to be fitted. The REM38E plugs were the correct type for
the engine. The REM40E plugs were of a higher heat range for use in
engines of a lower compression ratio. They were neither recommended
nor approved for this engine model. The manufacturer stated that
during the certification of the engines and spark plug approval, it
was determined that it was possible to experience
detonation/pre-ignition and serious engine damage with other than
the approved spark plugs fitted. The engine manufacturer further
advised that the mixing of spark plugs by heat range was not good
practice.
The spark plug manufacturer described detonation as the
explosion of unburnt fuel ahead of the normal flame front, and is
typified by a mildly rough running engine with an audible knocking
sound. Pre-ignition is the ignition of the fuel while the
compression stroke is occurring, but much earlier than intended.
Pre-ignition is typified by engine roughness and backfiring.
The only aircraft documents located were the engine and aircraft
radio maintenance logbooks, and some expired maintenance releases.
The aircraft and propeller logs, along with the current maintenance
release, were believed to have been destroyed in the post-accident
fire.
The aircraft's Lycoming IO-360-A1B6 engine, serial number
L-7866-51A, had been installed in the aircraft on 29 November 2000
following overhaul. The engine had approximately 35 hours in
service since installation. Documentation indicated that during the
overhaul, amongst other components, all of the camshaft followers
and the spark plugs were replaced. Only REM38E spark plugs were
listed as fitted. No documentation indicating fitment of REM40E
spark plugs was found. The engine logbook indicated that, on 22
February 2001, the fuel control unit was recalibrated, and the fuel
injector nozzles tested due to high fuel flow at take-off. The
logbooks indicated that during a subsequent engine run, the engine
operated normally.
A pilot who flew the aircraft on 17 May 2001 reported that,
following takeoff, he experienced an engine surge similar to a
change of propeller pitch towards coarse. After an adjustment of
the propeller pitch control the engine returned to normal. He
recorded the problem and mentioned it to the aircraft owner, who
indicated he would have the propeller system examined. No
maintenance records relating to this event were located.
Maintenance documentation available indicated that the propeller
governor had been repaired on 8 September 2000, and the propeller
had been repaired on 12 October 2000.
Witnesses reported that the aircraft had been refuelled from a
sealed drum on the afternoon of the day before the accident. Post
accident examination of a sample of fuel remaining in the drum
showed it to be free of water contamination. A detailed analysis of
the fuel, carried out by a National Association of Testing
Authorities (NATA) accredited laboratory, showed that it met the
requirements of 100 Low Lead Avgas. Witnesses indicated that a fuel
drain check was carried out prior to flight.
