Fire

The pilot was conducting a flight from Diamond Beach to Cooma. Approaching Hoskinstown the aircraft's rear engine suffered a loss of power and smoke appeared in the cabin. The pilot immediately shut down the rear engine and feathered the propeller. Because the symptoms indicated that a fire was burning in the rear engine compartment, the pilot decided to land as soon as possible, and prepared for an emergency landing into a paddock. During the approach the smoke disappeared from the cabin, so the pilot concluded that the fire had extinguished itself and discontinued the landing. He then diverted to Canberra, using the front engine only, where he landed safely. An examination of the rear engine compartment revealed that a large section of the left-hand exhaust stack had separated in flight. Hot exhaust gases, now directed into the rear engine compartment, burnt a hole through the lower cowl, distorted the firewall and burnt the insulation from electrical wires including the low tension ignition leads. The bare ignition leads then "shorted out" causing the engine to fail. The source of heat having been removed prevented the fire from becoming self-sustaining. Cracks of about 18 cm in length had occurred along either side of the lower welded seam from the muffler attachment flange. The forward crack propagated around the exhaust stack, through 180 degrees, and returned back to the muffler attachment flange, paralleling the lower seam. This allowed the section of exhaust stack to separate. Expert opinion suggests that the cracks should have been evident for a considerable period of time, having originated from normal thermal fatigue and exhaust gas flow erosion. The aircraft had been subject to a major inspection a short time prior to the flight. The organisation which performed this inspection advised that there had been no evidence of exhaust gas leakage, or cracks visible to the naked eye at that time.

Circumstances:

The pilot reported that while attempting to start the aircraft engine, he smelt smoke. All occupants evacuated the aircraft, and the pilot attempted to extinguish the fire in the engine compartment with the aircraft's two fire extinguishers. He was unsuccessful in his attempt and called for assistance. By the time the local fire truck arrived the aircraft had been destroyed by the fire. The degree of destruction was too extensive to permit any meaningful investigation into the cause of the fire.

The pilot had planned to carry out a cattle muster in conjunction with another aircraft. He had been late in departing his base but when he found the other aircraft had not yet arrived at the rendezvous point he decided to make a quick comfort stop. The helicopter was landed on a spinifex covered area and the pilot disembarked leaving the engine running. Shortly afterwards he noticed a fire underneath the helicopter and reboarded in an attempt to fly it away from the fire. The engine did not respond. The pilot disembarked and attempted unsuccessfully to extinguish the fire. He received burns to his hands and legs while unloading equipment and the helicopter was destroyed.

Circumstances:

During a short ferry flight to a property for the purpose of conducting shooting operations, the pilot noticed a burning smell in the cockpit and a glow beneath the rear seat. Following an emergency landing the pilot evacuated the aircraft before it was consumed by fire. The pilot reports that he had been carrying signal flares, fuel, oil, grease and dirty rags on and beneath the rear seat. He further reports he had been smoking prior to becoming aware of the burning smell. The Fire Officers Investigation report confirms that the fire had originated in the cockpit and that the source of ignition had probably been a lighted cigarette butt which had come to rest on the dirty rags.

The aircraft was cruising just inland of the beach at 1500 feet when the pilot noted smoke, accompanied by a strong burning smell entering the cabin from the lower right hand side air vent. Almost immediately the engine suffered a complete loss of power. The pilot carried out a successful wheels-up forced landing on the beach. A fire which had been burning in the nose wheelwell area had apparently been extinguished by seawater and wet sand during the landing slide. Inspection revealed that chaffing had occurred between an electric cable and hydraulic line situated in the wheelwell. Arcing from the electric cable burnt through the hydraulic line, and hydraulic oil under pressure escaped in a fine spray and was ignited by the arcing. This created a torching effect which was directed at the fuel strainer. The heat caused the fuel in the strainer to boil, developing a vapour lock and disrupting the fuel flow to the engine and causing the subsequent engine failure. The chaffing of the cable on the pipe was in such a location that it would have been difficult to see during normal periodic or pre-flight inspections.

Circumstances:

Approaching top of descent at 10,000 feet, the pilot noticed smoke coming from under the instrument panel. The smoke rapidly increased in density until it was almost black in colour with a very strong petrochemical, choking odour. The pilot commenced a rapid descent and turned the aircraft towards the coast. He switched off all electrical services as flames appeared under the instrument panel. He extinguished these flames with the cockpit fire extinguisher and opened the cockpit window to provide fresh air. The pilot switched on the electrics to transmit a mayday call and talk to a company aircraft about 10 miles behind. However, flames reappeared so the electrics were again selected off. At no time did any circuit breakers operate. Passing about 7,000 feet in the descent, the engine failed without warning and could not be restarted. The pilot manoeuvered the aircraft for a wheels up landing on a dry tea tree swamp. On final approach, he unlatched the door to aid in emergency evacuation. The passenger in the right front seat attempted to exit the aircraft but was restrained by the pilot. This passenger had to keep her feet on the seat during the final 300 feet to avoid the flames. The pilot planned a high-speed approach to ensure he did not undershoot the intended landing area. On short final, he selected full flap and, probably due to the short circuit behind the instrument panel, full flap was obtained. He also opened the air vents which increased the intensity of the fire but gave him good vision. After striking some small trees on final, the aircraft slid about 90 metres before coming to rest. All occupants evacuated safely through the doors. The pilot estimated that the cabin was engulfed in flames within 30 seconds of the aircraft stopping. It is most likely that the fire started as a result of electrical arcing caused by the failure of insulation on the wire carrying electrical power from the starter relay to the ammeter. The fire burnt through the magneto wire insulation, grounding the wires and stopping the engine.

Significant Factors:

The following factors were considered relevant to the development of the accident:

1. The insulation on the starter relay to ammeter wire on the cabin side of the fire wall rubbed through.

2. An electrical short circuit developed, resulting in arcing which started a fire under the right side of the instrument panel.

3. The fire spread to the left side of the instrument panel and burnt through the magneto wire insulation resulting in engine failure.

4. The aircraft landed in unsuitable terrain.

Circumstances:

The aircraft had reportedly been shut down for about an hour. After refuelling, the aircraft was started and the pilot noticed smoke coming from under the seat. He shut down the engine and by this time flames were seen under and around the back of the engine. The pilot grabbed a fire extinguisher and ran to another aircraft for assistance. Attempts to put out the fire were reportedly thwarted by the heat of the fire and as there was a significant quantity of ammunition on board, everyone hid behind a tree until the fire burnt out.

On arrival at Koolatah the pilot selected a grassed area alongside a track for landing. After landing he shut down the engine. Shortly afterwards flames were observed underneath the helicopter and the pilot and passenger abandoned the machine. The helicopter was completely destroyed by fire which had apparently been ignited by hot exhaust gases.

The aircraft was being flown to Waikerie for a major inspection. While the aircraft was cruising at 2500 feet enroute, the pilot stated that he smelt smoke and almost immediately noticed oil streaming over the windscreen. He closed the throttle and commenced an approach to a large paddock. The aircraft was landed without further damage. The pilot vacated the aircraft via the rear door to avoid the billowing smoke from the engine compartment and attempted to extinguish the fire with a portable fire extinguisher. On realising the attempt would be unsuccessful, he collected his luggage from the cabin of the aircraft and cleared the area. The aircraft was subsequently destroyed by fire. Inspection of the rear of the engine compartment was hampered by the degree of damage caused by the intensity of the fire. The investigation did not discover any malfunction that might have caused the fire.

The culler had just made a kill and the pilot prepared to land so that the beast could be bled. He selected an area of short grass and set the helicopter down with the engine over the barest area. Prior to landing the pilot briefed the culler on the need to deplane quickly to minimise the risk of a ground fire from grass ignited by the hot exhaust. The pilot intended to take-off as soon as possible and return for his passenger when the ground task was finished. Soon after the passenger had deplaned, the pilot was attempting to build up the rotor RPM when he became aware of smoke and flames. He reported that the engine was not responding to throttle input, and when he pulled the collective for liftoff, the engine lost all power and the helicopter settled onto the ground from a few feet. The aircraft was enveloped in flames as the pilot left the cockpit, and it was destroyed by fire. A fenceline cleared of grass existed some 70 metres away, but the pilot was intent of remaining clear of dust areas to prevent wear in the tail rotor assembly. He judged that there was a minimum risk of fire in the area selected for landing, and it was clear of the obstruction posed by the fence. There were no reported aircraft defects or fuel leaks.