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.
