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Summary

Summary

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.

 
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