The pilot of the Bell 206 helicopter had been tasked with conducting a survey operation in the Dhoyndji area of the Northern Territory. He had flown the helicopter from Gove earlier in the morning with two passengers on board. Some equipment was offloaded at Dhoyndji and another two passengers boarded the helicopter. The pilot departed Dhoyndji at approximately 1150 Central Standard Time (CST) and tracked to the southwest to commence the survey work. He initially tracked to the Goyder River and landed to the west of the river. The passengers conducted ground survey work in the area for 40-60 minutes. They then reboarded the helicopter and began aerial survey work in the same area for approximately 10 minutes. The pilot then flew the helicopter in a north-easterly direction towards the Mitchell Ranges.
At 1330 a refuelling party realised that the helicopter was overdue for a scheduled refuelling stop and that its SARTIME had expired. The aircraft operator and the refuelling party commenced a local search and CENSAR notified Australian Search and Rescue (AusSAR) of the expired SARTIME. AusSAR assumed responsibility for search coordination and the wreckage of the helicopter was found the following day. The pilot and three passengers received fatal injuries.
The survivor reported that as the helicopter approached the Mitchell Ranges, one of the passengers indicated that they would have to land in the area to conduct a brief ground survey. The pilot acknowledged the requirement and began to search the area for a landing spot. The surrounding terrain was generally flat and lightly treed. The tree spacing was such that a landing area was not readily apparent.
The survivor reported that he heard a single 'beep' in his headphones as the pilot searched for a landing area. The pilot looked into the helicopter cockpit and appeared to be checking his instruments. Shortly after, the pilot appeared to return to the task of selecting a landing spot. The survivor estimated that about 2-3 seconds after the single 'beep', he heard continuous 'beeping' in his headphones. He reported that the pilot told everyone to "hang on boys, this is going down".
The survivor was seated in the right rear seat of the helicopter, immediately behind the pilot. He reported that when the continuous beeping started, the helicopter "appeared to fall out of the sky". At that time, he estimated that the helicopter had been at a lower height, and a considerably lower speed than when flying from the Goyder River area to the Mitchell Ranges.
The Pilot
The pilot held a Commercial Pilot (Helicopter) Licence with an endorsement on the Bell 206 series helicopter. He had accumulated 5,455 hours total aeronautical experience with 5,330 hours on the Bell 206 helicopter. He held a Class 1 medical certificate with a condition that vision correction be worn while exercising the privileges of the licence. The pilot was reported to have always worn his glasses. The survivor reported that the pilot was wearing his glasses when the helicopter departed the Goyder River area.
The pilot was adequately rested prior to commencing the survey and had not exceeded any flight or duty times. He had flown his entire career in the Arnhem Land area and was considered by his peers to be a meticulous and safety conscious pilot.
The helicopter
The helicopter had completed 8,226.5 hours of flight time. All required maintenance had been completed. It last underwent maintenance 3 weeks prior to the accident. During that scheduled maintenance, the main rotor transmission was overhauled. The helicopter had since completed 24.6 flying hours. There were no reported problems with the helicopter during that period.
The engine fuel control unit was last removed from the helicopter in February 2002, as the engine was not achieving predicted starting performance. The fuel control unit was repaired in accordance with the manufacturer's overhaul instructions and refitted to the helicopter. The engine subsequently started normally.
The helicopter was refuelled to full tanks at Gove on the evening prior to the day of the accident. Two additional 200 litre drums of fuel were taken from the same fuel supply and road transported to the Dhoyndji area for use during the survey. Search aircraft subsequently used this fuel with no problems being reported. Analysis of the Gove fuel supply revealed it was of the correct aviation turbine fuel specification and contained no contamination. It was estimated that the helicopter had approximately 150 litres of fuel remaining on board at the time of the accident. The survivor reported that he had been covered in a liquid after the helicopter's impact with the ground. He described it as being consistent with aviation turbine fuel.
At the time of the accident the helicopter was within weight and balance limitations.
Wreckage examination
The advancing main rotor blade had collided mid span with a tree that was about 30 cm in diameter. The helicopter then impacted the ground heavily on its left side. A severe post-impact fire consumed most of the wreckage. The wreckage trail, including the engine, engine compartment, transmission and hydraulics pack, was orientated along a bearing approximating 155 degrees magnetic. The distance from the base of the tree to the main wreckage area was approximately 15 metres.
The retreating main rotor blade was found lying leading edge down and in a normal orientation to the main wreckage. No leading edge deformities were found on this blade. Both main rotor blades remained attached to their respective rotor grips and to the main rotor mast. The main rotor mast exhibited a slight bending towards the advancing blade.
The main rotor transmission remained attached to the fuselage-to-transmission 'A' frame supports. Examination of the transmission magnetic chip detector found no debris adhering to the plug and the remaining transmission oil was clear of contamination.
Both tail rotor blades remained attached to their respective grips, and to the tail rotor gearbox assembly. The blades exhibited minor leading edge impact damage consistent with low speed rotation through light tree branches. The tail rotor gearbox magnetic chip detector was clean and free of debris.
All flight control tube rod structures had been consumed during the fire. A search of the wreckage found the control tube rod junction bolts securely fastened and lock wired.
The fire had completely destroyed the accessory gearbox housing and all attached ancillary components. The remainder of the engine was recovered for off-site examination.
The inspection of the engine was carried out at an authorised overhaul facility, under the supervision of the Australian Transport Safety Bureau and observed by a representative of the engine manufacturer. The engine compressor and power sections exhibited signs of rotation, but not power, at impact. The reason the engine failed could not be determined due to the extensive fire damage to the accessory gearbox and other engine components.
The survivor was played a number of randomly sequenced warning tones that had been recorded from a similar Bell 206 helicopter. He identified the continuous 'beeping' as that of the engine-out audio warning tone. He also described the single 'beep' as the commencement of the engine-out audio warning tone. The helicopter Flight Manual stated that the engine-out warning tone warned the pilot of an engine power failure.