Bell Helicopter Co 206B(II), VH-FVF

The pilot continued to fly after consulting a doctor regarding
severe headaches with vision disturbances.

The aircraft

A detailed examination of all available parts of the helicopter
concluded that the engine was most likely to have been operating
and driving the main and tail rotors. Consideration was given to
failures that could cause an uncommanded descent or turn in flight.
However, the investigation considered it unlikely that an
experienced pilot would allow the helicopter to smoothly descend to
collision with the ground.

No evidence was found of any pre-existing defect or malfunction
to the aircraft that may have contributed to the development of the
accident.

The flight path

Under the prevailing conditions, the investigation considered
that the track flown by the helicopter was in keeping with the
pilot's normal routine. The unusual aspect of the flight path was
its inappropriately timed descent.

The helicopter was reported to be in a smooth flight path, with
no jerking and no abnormal sounds such as would be produced with an
engine power change or sudden control inputs. On impact with the
trees, the helicopter was in a steady flight regime,
laterally-level and descending at about 1,200 ft/min. This could
indicate that the pilot was maintaining his grip on the cyclic
control. If the cyclic control was released, it would most likely
have fallen to some abnormal position in a short time. This could
have caused the helicopter to adopt an unusual attitude very
quickly. The conclusion, therefore, is that the pilot may have been
able to maintain control in some form or other: from fully
conscious, to a situation where he had managed to "freeze" on the
controls and simply maintain them in position.

If the pilot was fully conscious, then the flight path may have
resulted from a distraction. However, no evidence was found of
anyone making a phone call to the aircraft around the time of the
accident. In any case, it is unlikely that an experienced pilot
flying at low altitude toward rising terrain would allow himself to
become distracted for the time involved in this accident sequence
(about 15 secs) and not pay any attention to the flight path.

The pilot

The pilot had visited a DAME a few weeks prior to this accident.
This was as a result of headaches that had increased in severity
and involved vision disturbances. The ENT specialist found a
suspected sinus infection and prescribed a course of antibiotics.
The investigation found no underlying personal factors, other than
the headache problem, that may have played a role in this accident
sequence.

There is no evidence that the pilot complied with the relevant
regulations, other than his initial referral of the problem to a
DAME. CAR 6.16A imposed a condition on the pilot that he not resume
flying duties until being cleared to do so. It is likely that the
pilot was reluctant to cease his normal duties unless strongly
advised. The DAME had not yet reported the pilot's medical
situation to CASA. Consequently, CASA were not in a position to
take more positive control of the case.

The pilot was flying the Bell Jetranger from Archerfield to his
home base at Channel 10 on Mount Coot-tha. The flight continued
normally until passing the Channel 9 buildings situated on the
southern end of Mt Coot-tha. Approaching that area at 1,000 ft, the
pilot apparently intended to track to the western side of Mt
Coot-tha for a landing at the Channel 10 pad. When passing abeam
the Channel 9 tower at about 850 ft, the helicopter was seen to
enter a descending right turn until it struck trees and the ground
600 ft above sea level on the western slopes of Mt Coot-tha. The
helicopter collided with the trees in a laterally-level attitude,
with no roll rate, a descent angle of about five degrees, and a
speed estimated to be its normal cruise speed. A fire erupted
immediately and consumed the helicopter. The pilot was fatally
injured as a result of the impact.

Accident locality

Mount Coot-tha is the location of the television transmitting
towers for the Brisbane area. Channel 9 is the southernmost tower
and Channel 10 is the northernmost tower. Each television station
has a helicopter landing site and associated flight paths. As a
standard practice, each television station pilot was aware of the
others' normal approach and departure procedures and avoided the
relevant areas during flights.

The pilot involved in this accident had developed a practice of
monitoring the movements of the Channel 9 and Channel 7
helicopters: he would check on their presence while flying to or
from his landing site, if the intended flight path took him near
the other stations. On the accident flight, this could have been
achieved by flying to the west of the mountain.

After passing abeam the Channel 9 area at about treetop height,
the route to Channel 10 involved crossing a ridgeline. The ridge
was about the same height as the mountain and would have required
the helicopter to maintain altitude or climb slightly to cross the
ridge.

Weather conditions at the time were suitable for the flight. The
wind was light, with an easterly to south-easterly tendency.

Personnel information

The pilot held an Airline Transport Pilot Licence (Helicopter)
with a current Class 1 medical certificate, with vision correction
required. He had accrued considerable aeronautical experience in
both aeroplanes and helicopters. Of this, 7,566.2 hours had been
gained in helicopters. His most recent competency check had been a
Biennial Flight Review conducted on 12 and 13 August 1998. His most
recent medical examination for the issue of a flight crew medical
certificate had been conducted in June 1998.

Flight and duty time records maintained by the pilot indicated
that he flew the accident helicopter regularly. In addition, he
regularly flew a fixed-wing aircraft, normally at fortnightly
intervals. His flight and duty time sheet recorded having
specialist medical appointments on 10 and 14 August.

Little examination of the pilot's activities and eating habits
in the few days prior to the accident was possible. The pilot had
recently been under some personal emotional stress. However,
information received from colleagues and friends indicated that the
current life stress did not appear to have impaired the pilot's
routine behaviour and functioning.

Aircraft information

The helicopter was a Bell 206B Jetranger, serial number 1946,
manufactured in 1976. It was maintained for operations in private,
air work, and charter categories involving flights under the visual
flight rules by day or night. Up to the morning of the accident
flight, it had accrued 4,532.8 hours time in service.

Three months before the accident, an entry in the maintenance
required section of the maintenance release stated "high pitched
noise / vibration through airframe at speeds 100 kt +". The
clearing endorsement indicated that the helicopter was inspected
thoroughly and the inspection doors on the right and left sides had
been reshaped to fit more snugly. The entry contained a pilot's
clearing signature for the subsequent test flight.

The high speed / high frequency vibration problem was reported
to have persisted for some years prior to the accident and attempts
to positively isolate the problem had been unsuccessful. Its
intermittent nature made troubleshooting difficult. The noise was
reported to be present in cold air conditions more consistently
than in warm conditions. After considerable discussion with pilots
who had experienced, or had attempted to induce the problem, the
investigation concluded that the problem was most unlikely to have
arisen on the accident flight. In any event, the problem was
considered to be unrelated to the controllability of the
helicopter.

An examination of all maintenance records did not reveal any
other aspect considered likely to have contributed to the
accident.

Communications

The helicopter was fitted with a mobile telephone and the pilot
routinely carried a pager. Answering the phone involved
manipulating a panel on the centre console area to the left of, and
slightly behind, the pilot. No evidence of any calls made to the
telephone or the pager was found.

Recorded voice communications and radar data for the flights to
and from Archerfield were examined. The data indicated that the
helicopter was flown normally during the flights.

Wreckage and impact information

The helicopter's initial impact was with the top limbs of a dead
tree, followed soon after by collision with a large gum tree. The
main rotor blades severed the top half of the tree and the airframe
shattered the bottom half, allowing the top half to fall beside the
tree stump. Loud bangs heard by witnesses were consistent with
these impacts and also with the outbreak of the ensuing fire. The
helicopter's speed at the time of impact was estimated to be around
110 kts, its normal cruising speed. Its descent angle of five
degrees was consistent with a descent rate of about 1,200
ft/min.

Although the fire consumed most of the airframe, there were
sufficient parts available for specialist examination. The
investigation concluded that the engine was operating at impact,
and the engine was driving the rotor systems. Rotor control systems
were also intact, as far as could be examined. A trailing edge
balance weight at the inboard end of a main rotor blade was not
found. Specialist examination determined that the mounting point at
the outboard end of the weight had been fractured for some time
prior to the accident flight and that the inboard mounting point
had also developed a fatigue crack. The investigation could not
establish whether the balance weight finally became detached as a
result of impact during the accident sequence or prior to impact.
Representatives of the helicopter manufacturer considered that the
absence of the balance weight would not have affected the
helicopter's controllability. The investigation found no
pre-existing defects likely to have contributed to the
accident.

Helicopter controllability

The investigation considered a number of possible failures that
could have been encountered during the flight. Witness reports were
consistent with recorded radar data that indicated the flight path
was smooth, with no unusual noises or abrupt movements of the
helicopter. At impact, the helicopter was laterally-level and at
high speed. The cyclic control movement needed by a pilot to
transition from level flight to a descent angle of about five
degrees (corresponding to a descent rate of 1,200 ft/min) was
reported to be about 12 mm. The investigation was advised that an
experienced pilot would normally be aware of this amount of cyclic
control movement.

Loss of tail rotor control in the cruise was considered and
assessed as not being a significant immediate problem, due to the
speed of the helicopter at the onset of the accident sequence. The
pilot could have turned away from the mountain towards the valley
to the left, where appropriate decisions could be made without the
need to avoid terrain.

Possible jamming of the hydraulic system associated with the
main rotor controls was considered. If a failure caused a control
deflection fully one way suddenly, an abrupt flight path deviation
and change in aircraft noise would be expected. Similarly, a jammed
control should also be likely to produce some abrupt movements, at
least initially. Both problems should have been controllable by the
pilot as the aircraft hydraulics are designed to be
overpowered.

Had engine power loss or surging occurred, these should have
produced some audible changes in noise from the engine and the
rotors. A turn initiated by the pilot toward the lower ground,
climb and slowing of the helicopter would also be expected.

A bird strike, or some other event affecting the pilot, was also
considered. If the pilot had been incapacitated to the extent that
he was unable to control the helicopter, then the flight path would
be expected to have changed in some way. Experienced pilots
interviewed during the investigation indicated that if the cyclic
control is released it should remain in position for a few seconds
and then start to fall in a random direction. The rate of change
could increase if the control diverged from the central point. This
could produce obvious changes in aircraft noise and flight
path.

Medical information

Medical evidence provided to the investigation indicated that
the pilot had suffered from a subarachnoid haemorrhage, for which
no bleeding vessel could be found, in June 1994. His flight crew
medical certificate had been cancelled as a result of that event. A
Class 2 medical certificate was issued as a result of a medical
examination in June 1995. His next medical examination was in July
1996 and Class 1 and 2 medical certificates without restriction
were issued in August 1996. Further routine flight crew medical
examinations were subsequently passed in June 1997 and June
1998.

On 28 July 1998 the pilot attended a designated aviation medical
examiner (DAME), reporting that he had begun to experience severe,
migrainous type headaches with blurred vision and instances of
double vision. The DAME considered that there was a strong
possibility that emotional stress was the cause. Since the symptoms
did not match the normal indications of migraine headaches, the
doctor referred the pilot to a neurologist for specialist
examination. The DAME also indicated that the patient was a pilot
and asked for advice concerning whether he should continue flying
(the pilot was keen to continue flying). The pilot initially
consulted the neurologist on 5 August and a follow-up meeting was
held on 10 August. With no neurological problems evident as a
result of that examination, he was then referred to an ear nose and
throat (ENT) specialist who diagnosed a severe sinus infection. The
specialist prescribed a course of antibiotics. That visit had taken
place on 14 or 17 August. No information on the speed of onset of
the headaches was available.

The neurologist involved in the 1994 event was the same person
involved in the pilot's recent specialist examination, and had
concluded that the pilot's current symptoms had not been related to
the pilot's previous medical history.

Evidence available to the investigation indicated that the pilot
had suffered a headache early in the morning of the accident flight
and some Channel 10 staff reported that he did not appear to be
well on arrival at work. On the other hand, other people familiar
with the pilot had attended the meeting at Archerfield and reported
that he seemed normal at that time.

Post-accident advice from the Civil Aviation Safety Authority
aviation medicine staff indicated that, based upon information
obtained from the medical practitioners, the pilot had experienced
a change in his medical condition so that he no longer met the
required medical standard.

The limited post-mortem information available did not assist
with an assessment of the pilot's physiological state at the time
of impact. There was insufficient post-mortem evidence to determine
if any neurological anomalies had contributed to the accident.

Medical regulations

Considering that the pilot had experienced recent medical
problems and had consulted a DAME, the relevant Civil Aviation
Regulations (CARs) were examined. Anecdotal evidence indicated that
the DAME could have advised the pilot as to whether or not he could
continue with his flying duties. CAR 6.16A also indicated that the
pilot was not permitted to fly, pending a resolution of his medical
situation.

CASA normally provides each DAME with more detailed guidance on
the matters considered significant to aviation. The neurological
section described different forms of headaches and the
considerations involved with each type. In relation to the type of
headache considered likely to involve this pilot, the guidance
stated, "Such migraines are characterised by long periods of
remission and capricious onset, and may completely incapacitate the
sufferer. All cases will be considered on an individual basis."