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."