Survival
The pilot survived the crash but suffered multiple injuries. He
undid his safety belt on the right front seat and exited the
helicopter from the damaged left side. However, he died before the
wreckage was located. The accident was potentially survivable. The
pilot carried his flying helmet in the helicopter but had elected
not to wear it for the ferry flight. He suffered serious head
injuries.
Pilot information
The pilot held a Canadian commercial helicopter pilot licence.
He was endorsed on the Bell 205. His total flight time was 10,092
hours, of which 9,992 had been flown in helicopters. He had flown
approximately 3,600 hours in the Bell 205. His last company flight
cheek was on 13 June 1995. He passed his last aviation medical
examination on 7 November 1995. He was experienced in carrying out
helicopter fire-fighting operations.
Medical information
The pilot's medical certificate required the use of vision
correction lenses when flying. Evidence at the accident site
indicated that he was probably wearing spectacles at the time of
the accident. The only physiological condition subsequently found,
which may have slightly affected his flying performance, was due to
skin irritation, after being doused with jet fuel while refuelling
just before departing Cockatoo.
Damage to aircraft
The helicopter was destroyed during the impact sequence. There
was no post-impact fire.
Weight and balance
The helicopter was within its approved weight-and-balance limits
at the time of the accident.
Weather
The wind was reported to be north-westerly at about 5 kts. The
cloud was one or two oktas of stratocumulus at 5,000 ft. Visibility
was in excess of 10 km. The weather was not a factor in the
accident.
Aids to navigation
The helicopter was equipped with a global positioning system
(GPS) which would have allowed the pilot to accurately fly a direct
track to Benalla.
Wreckage information
No fault was found with the airframe or electrical systems of
the helicopter. On-site examination of the wreckage indicated a
loss of drive from the engine to the main transmission. The core
engine was found to be physically disconnected internally from the
main engine output gearbox. The engine chip detector was found to
be heavily contaminated with metallic debris. A subsequent engine
teardown inspection identified that the engine output gearbox had
suffered significant damage and was the source of the drive
failure. A discontinuity found in the engine chip detector wiring
was assessed as impact damage.
Maintenance summary
Maintenance history was obtained from journey logs, engine logs
and Transport Canada Aircraft Technical logs (engine and airframe).
The following is a summary of maintenance data relevant to the
engine fitted to GFHO at the time of the accident:
- 04 Apr 1992; engine, serial number LE-07683C, upgraded from
T53-13B to T53-17A configuration at 6,624 hours time since new
(TSN). - 16 May 1994; engine LE-07683C overhaul completed at 7,020.4
hours TSN. - 17 Aug 1994; engine LE-07683C fitted to GFHO.
- 05 Sep 1995; governor input seal leaking. Governor assembly
replaced with overhauled unit. - 08 Sep 1995; GFHO last flight in Canada.
- 25 Sep 1995; 100 hr inspection complied with in accordance with
Bell 205 M & 0 and Lycoming manuals. Engine chip plug contains
small amount of fuzz. All remaining screens and detectors found
free and clean of debris. - 29 Sep 1995; engine LE-07683C accessory gearbox, serial no.
4029 replaced when copper-coloured metal contamination was found in
the airframe paper filter. Accessory gearbox, serial no. 5154-6
(17.5 hours time since overhaul) fitted in accordance with Lycoming
MM. Ground run & leak check complied with. - 04 Oct 1995; helicopter GFHO disassembled and shipped to
Australia. - 24 Nov 1995 (late entry 19 Dec 95); engine LE-07683C, N2
torquemeter boost pump, serial no. Cl 198 replaced when "oil not
scavenging from N2 gearbox and brass found in engine filters". N2
torquemeter boost pump, serial no. LA7278 fitted. "Pump removed has
internal damage to brass bushings and the shaft has moved forward
and uncoupled from pump". - 28 Nov 1995; helicopter GFHO reassembly completed in
Australia. - 29 Nov 1995; GFHO first flight in Australia.
- 13 Dec 1995; at the time of the accident, engine time logged in
Australia approximately 4.5 hours, engine had accumulated
approximately 7,413.0 hours TSN and therefore 392 hours time since
overhaul (TSO).
Post accident maintenance observations
- Oct 1995; according to the operator, the accessory gearbox
removed on 29 Sep 1995 was disassembled and found to be acceptable
for continued use and not responsible for the oil contamination
found in the filter. It was decided that the N2 torquemeter boost
pump may have caused the metal contamination and that this should
be replaced when the aircraft was re-assembled in Australia. - 24 Nov 1995; the torquemeter boost pump, as well as suspected
to be the source of metal contamination, was considered to be
responsible for a previous oil leak. According to the operator, the
oil leak mentioned was discovered during the governor change on 5
Sep 1995. Subsequent inspection of the replaced pump found
incorrect assembly had led to gouging of a brass bushing and
generation of brass contamination.
Engine teardown inspection
An engine teardown inspection revealed that the helical sun
gearshaft was uncoupled from the output reduction gearbox. The
helical sun gear is coupled to the power shaft and drives the
reduction gearing. Output power is extracted from the reduction
gearing through an externally splined output shaft. The uncoupling
resulted in the loss of drive from the engine to the main
transmission. Disassembly also revealed:
- Copper/brass and steel particles contaminated the oil
system. - The helical sun gear (PN 1-030-192-04) had apparently
overheated and all its teeth had been machined off by the three
mating planet gears mounted on the reduction gearbox carrier
housing assembly. The input gear teeth of the planet gears were
extensively damaged, the involutes being filled with smeared metal.
Two helical sun gear teeth appeared to have fractured as a result
of fatigue crack growth prior to the general destruction of the
gear. A gear tooth fragment, matching the remnant of the helical
sun gear tooth fracture, was found in the coarse filter screen of
the oil pump. - The N2 tachometer drive spur gear (PN 1-070-062-04) was loose
on its shaft. The nut (PN MS 172237) and nut retainer (cup washer)
(PN 1-070-066-01) securing the gear to the shaft were missing from
the assembly. The nut was found loose in the accessory drive
carrier assembly. The nut retainer, used to lock the nut on the
shaft, was found in the scavenge strainer screen of the accessory
drive gearbox, with a broken locking tang. Movement of the spur
gear resulted in impact and damage to the drive spur gear teeth on
the power shaft, reduction gearbox outer housing and No 21 bearing
clamping plate. - The sleeve bushing of the N2 tachometer drive gear assembly had
moved out of its housing and the lower bearing cage had failed. The
sleeve bushing retention pin (PN AN122683) missing from the
assembly was located in the metal debris subsequent to the teardown
inspection. The retention pin hole on the sleeve bushing was not
properly located with respect to depth and location. - The engine oil pump, mounted on the accessory drive gearbox had
seized. The input drive shaft had sheared. A metal sliver (5mm x
2.5mm) jamming a pump impeller blade had caused the seizure. The
chip detector was completely covered in particles. - Extensive metallic debris was found in the accessory drive
gearbox assembly, however, the drive gears and bearings were
undamaged. The scavenge strainer screen was blocked with metal
debris. Some of the debris was identified as a cup washer from the
N2 tachometer drive spur gearshaft and a helical sun gear
tooth. - The sun gearshaft roller (No. 21) bearing (PN 1-300-082-03M)
had completely failed, with no roller elements remaining. A visual
examination assessed the failure to be as a result of metal
contamination and oil starvation. The power shaft acting as the
bearing inner race had been damaged as a result of excessive heat
and the skidding rollers of the bearing. - The forward compressor ball bearing and aft compressor roller
bearing, mounted on the power shaft, suffered damage consistent
with oil starvation. - The torquemeter boost pump fitted to the engine at the time of
the accident was found to be undamaged, correctly assembled and
free to rotate.
Reduction gearbox carrier housing assembly inspection
The sun helical and planetary gear is located in the reduction
gearbox carrier housing assembly (PN 1-030-340-04). Examination of
the GFHO carrier housing assembly following the accident revealed
that:
- The roundness (degree of ovality) of the aft bearing bores was
up to 8 times greater than the allowable tolerance of 0.001 inches.
The concentricity or alignment of the small bearing (aft) bores
with the large bearing (front) bores was found to be up to 25 times
greater than the allowable tolerance of 0.001 inches. - The carrier housing large bearing (forward) bores were within
tolerances. - The lack of parallelism between the front and rear plates was
found to be up to 7 times greater than the allowable tolerance of
0.001 inches. - The bores displayed evidence of fretting damage.
- The carrier assembly did not have a vendor manufacturing code
(required for civil certified components) etched into its
surface.
Engine maintenance records recovered by the Transportation
Safety Board of Canada, indicated that repairs at the last engine
overhaul included the chrome plating and grinding of the six
bearing bores of the carrier housing assembly in accordance with
the T53 overhaul manual. The concentricity and roundness of the
front and rear bore holes of the carrier housing assembly were
within limits at the time of the overhaul.
ELT and mobile telephone
After the accident both ELTs carried in the aircraft were found
to be switched off. The Narco ELTIO which should have been selected
to ARM in compliance with company policy, had the capacity to be
activated by crash impact if ARM had been selected. Both survival
beacons were found to be capable of normal operation after the
accident.
The pilot had access to a mobile telephone fitted to the
helicopter. However, even if he had been able to reach it he would
not have been able to use it to alert authorities of the accident
because the battery had separated from the telephone during the
accident. When a serviceable battery was subsequently fitted, the
telephone operated normally. The telephone installation was also
connected to the aircraft power supply. Inspection of the aircraft
indicated the power supply plug had been pulled from the telephone
in the accident. Also, severe impact damage to the helicopter's
nose area had severed one of the aircraft electrical cables at its
point of attachment to the battery relay.
Flight following
Two very high frequency (VHF) radios were fitted to the aircraft
for flight following with air traffic services. However, the pilot
elected not to use these radios for monitoring of the flight by
Airservices Australia. Instead he contacted the DCNR airdesk radio
operator and advised of his departure time. The radio he used for
the call was provided by DCNR to allow communications on the
Victorian public sector mobile radio network (SMR). This equipment
was not compatible with the aviation communications network. The
pilot used the "trunked" function of the SMR equipment, whereby
communications could only be heard by the person transmitting and
the person at the specific station the pilot was calling.
The airdesk operator provided "flight following" for the flight.
Under the DCNR monitoring system, the pilot was required to make
radio contact with the operator at least once every 30 minutes.
Following the departure call from Cockatoo, the airdesk operator
received no further calls from the pilot. At 1720, the airdesk
operator called the helicopter by radio and also by telephone but
received no response. At 1725 the airdesk operator contacted the
Benalla rappelling crew which was expected to train with the
helicopter in the next day or so. A crewman advised that he had
called the pilot on the trunked radio at 1636, to ask when the
helicopter was expected to arrive at Benalla. The pilot's response
was that he would arrive in about 35 minutes (1711 ESUT).
Search and rescue
At 1736 the DCNR airdesk operator contacted Melbourne Flight
Service to establish if the pilot of GFHO had transmitted any
flight details to Airservices Australia. The Flight Service
operator advised that no radio calls had been received from the
pilot. At 1802 the DCNR operator advised Melbourne Flight Service
that the helicopter was missing. The Flight Service operator in
turn relayed the information to the Melbourne Search and Rescue
officer. The uncertainty phase of search-and-rescue (SAR)
procedures was activated at 1806. Unsuccessful checks to locate the
helicopter were made by SAR staff. At 1840 the alert phase was
activated. At 1919 the distress phase was activated, 2 hours and 8
minutes after the pilot's estimated time of arrival at Benalla.
Search activities continued throughout the night. By the morning of
14 December a large-scale search was under way with 24 helicopters
and seven fixed wing aircraft used in the search.
By 1822, on the previous day, the Australian company operating
the helicopter had dispatched a helicopter to search for the
missing Bell 205. The search pilot estimated that GFHO could have
been somewhere in the Marysville area when 35 minutes flight time
from Benalla, so he tracked direct to Marysville to commence the
search and continued searching while monitoring the ELT distress
frequency until 2048, last light being 2101. Marysville is 5.5 km
SE of the accident site.
Search co-ordinators and search aircraft focused efforts in the
early stage of the search on identifying the source of transmission
signals on the distress frequency in the Strathbogie area, about 61
km N of Buxton.
Several people had seen and heard the helicopter minutes before
the crash. A couple had heard what was, in hindsight, probably the
sound of the helicopter crashing. These people did not hear or see
enough to convince them that an accident had occurred. However,
they listened to or watched the evening news and when nothing was
mentioned about a helicopter accident or a missing helicopter, they
did not contact the police. The search authorities made no public
media release of the missing helicopter until about 0630 on the
morning after the accident. As a result of the media release,
police received the first of several public reports of sightings of
GFHO between Buxton and Narbethong on the previous evening.
Narbethong is 13 km SSW of the accident site. At 0645 police
search-and-rescue officers dispatched two units to the Buxton area.
At 0916 a police helicopter crew spotted the wreckage of GFHO while
searching an area of reported sightings near Buxton the previous
day. Most of the sightings were reported to police as a result of
the media release. The accident site was 5 km right of the direct
track from Cockatoo to Benalla.
Autorotation
Autorotation is the means by which a pilot may safely land a
helicopter in the event of no engine power driving the rotors. In
single-engine helicopters, loss of drive to the main rotor normally
occurs as a result of engine failure. When the engine gearbox
failed in GFHO, the engine power output to the main rotor
transmission was effectively uncoupled but the engine possibly did
not stop immediately. Loss of drive to the main rotors, excluding
engine failure, is a very rare event necessitating action by the
pilot to effect entry into autorotation in order to maintain rotor
RPM. The gearbox failure resulted in metal debris seizing the
scavenge oil pump causing overload shearing of the oil pump input
shaft; this resulted in sudden loss of engine oil pressure, rapid
engine overheating and power loss.
According to the approved flight manual for the Bell 205, the
optimum airspeed for an autorotative descent, at a gross weight
above 7,500 lb, is 55 to 60 kts. In the case of GFHO, the rate of
descent in a stabilised autorotation would have been about 1,900
ft/min. At 35-45 ft above the ground (or in this case above the
trees), the pilot flares the helicopter which decreases both the
rate of descent and the forward airspeed, followed by levelling the
helicopter and increasing collective pitch at about 4 ft. Correct
autorotative technique ensures that the helicopter arrives on the
ground or contacts the tops of the trees with virtually no rate of
descent and very low forward airspeed. For an autorotation into the
trees, zero airspeed is preferred at the top of the trees. The
ground distance covered from the moment of engine failure to
entering a stabilised autorotation to touchdown varies according to
the pilot's time to assess and react, airspeed at entry, gross
weight of the helicopter, temperature, wind velocity and, in
particular, the height above ground or tree tops when the
autorotation commences. If the height is greater, so is the
potential range.
Evidence at the accident site indicated that GFHO probably had a
descent rate of about 500 ft/min and a forward airspeed up to 50
kts when it impacted the trees.