The helicopter company's operations, based at Cairns Airport, Queensland, included passenger charter flights between The Pier, at Cairns Harbour (4 km SE Cairns Airport) and Green Island (22 km NE Cairns Airport).

At about 1035 eastern standard time the pilot departed The Pier for Green Island in a Bell 206 helicopter with six passengers on board. Because of the likelihood of mechanical turbulence in the lee of the high terrain south of Trinity Inlet, he initially tracked via the Cairns Harbour shipping channel. When he reached the end of the shipping channel, he was unable to see the island because of rain so he descended from his cruise altitude of 500 ft to about 300 ft and was then able to see the island about 9 km ahead. The helicopter arrived at Green Island at about 1045.

At 1130, the pilot departed Green Island for The Pier with six passengers on board. There was light drizzle falling at the time but he assessed that conditions in the area were suitable for flight utilising external visual reference. The pilot again elected to track via the shipping channel. Clearance to enter the Cairns Control Zone was not immediately available because of other traffic, so the pilot conducted a number of orbits in the helicopter until he was issued with a clearance at about 1139 to track to The Pier via the shipping channel, not above 500 ft. The controllers advised the pilot that, within 7-9 km from The Pier, the cloud base was 800-1,000 ft, with some showers, and visibility less than 10 km.

As the pilot continued tracking along the shipping channel, using the channel beacons as track markers, he noticed that the weather conditions ahead were deteriorating. A short time later, he descended the helicopter to about 150 ft to keep the water surface in sight, and reduced speed. At about 1143, the controller cautioned the pilot that a parasail was operating in the Cairns Harbour area. A short time later, the pilot received a request for his arrival time from the company's office at The Pier. He responded that he expected to arrive in 5 minutes.

The pilot later reported that by that time the weather conditions had deteriorated further, he was flying at 50 ft or less above the water in light to moderate rain and could no longer see any channel beacons. He selected the windscreen demister on as condensation had begun to form on the inside surface. He also armed the inflatable floats that were fitted to the skid-type landing gear.

At about 1146, the pilot asked the controller for directions to The Pier. The tower controller advised that The Pier was on a bearing of 205 degrees M, at a range of 1.5 NM (3 km). At about that time, in-flight visibility rapidly deteriorated to an extent where external visual cues were not available. The pilot, noticing that the altimeter was indicating 100 feet, placed the helicopter in a gentle descent in an attempt to keep the surface of the water in sight. The helicopter contacted the water a short time later and rolled inverted. The pilot and five passengers quickly escaped from the fuselage to the surface of the water. One passenger was trapped in the cabin for a number of minutes and did not survive the accident.

The helicopter was certified for flight under the Visual Flight Rules and was equipped with a satellite navigation system receiver. Inflatable floats were attached to the skid type landing gear. These could be inflated by the pilot in the event of a water landing. The helicopter was not fitted with a radio altimeter.

The Cairns area was under the influence of south-easterly stream weather. The Bureau of Meteorology issued an amended aerodrome forecast for Cairns at 0808 for the 24-hour period from 1000. The forecast was for an easterly wind at 15 kt, visibility of 9,000 m, and light rain. Some cloud patches were expected with a base of 800 ft, a broken layer at 1,800 ft, and overcast at 10,000 ft. Periods of up to 1 hour of heavy rain, scattered cloud at 800 ft, and broken cloud at 1,500 ft were expected over the forecast period.

Controllers on duty in the tower indicated that the weather conditions had been fluctuating significantly and rapidly throughout the morning. There were periods when conditions met the criteria for VFR flight. This contrasted with intervals of low cloud and very heavy rain, amongst the worst conditions they had seen at Cairns. Radar images and rainfall rates suggested that visibility in the area of the accident could have been reduced to a few hundred metres or less. Personnel who were at The Pier at the time of the accident described the rainfall as torrential, with visibility as low as one car length.

A weather radar system operated by the Bureau of Meteorology was located at Saddle Mountain, approximately 11 km north-west of Cairns Airport. The weather radar data recorded at 1150 showed an area of moderate rainfall centred over Cairns Harbour, adjacent to Cairns City. It extended about 5.4 km north-south and about 3.6 km east-west.

The weather information the controller passed to the pilot was based on his visual assessment of the weather in Cairns Harbour as he saw it from the control tower. When the controller issued the caution to the pilot regarding the parasail, the radar indicated altitude of the helicopter was 100 ft.

The Bureau of Meteorology advised that conditions of minimum visibility at Cairns Airport occurred during the period between about 1155 and 1210. The recorded rainfall of 5.8 mm between 1150 and 1210 at Cairns Airport was similar to that which would be encountered in thunderstorms. Although there was an automatic weather station at Green Island it was not equipped to measure rainfall.

Examination of recorded Air Traffic Services radar data provided information on the track, altitude, and groundspeed of the helicopter for a portion of the flight. The data indicated that the helicopter was initially tracking via the Cairns Harbour shipping channel at about 100 kts and an altitude of 200 ft above mean sea level. At about 7 km from The Pier, the speed gradually decreased to 55-60 kts and then to below 40 kts. The last recorded speed was 31 kts. The recorded altitude during the final 2 minutes of the recording was 100 ft, apart from one value of 200 ft. The last recorded position of the helicopter was 2.4 km north-east of The Pier at about 1148.

Examination of the wreckage confirmed that the helicopter struck the water in a slight left skid-low, nose-low attitude, and at low forward and vertical speeds. All seats and safety harnesses retained their integrity. There was evidence of flexing of the roof frame on the right forward side of the cabin, immediately behind the pilot's seat resulting from induced stresses following main rotor blade contact with the water.

The postmortem examination report stated that the non-surviving passenger had received a minor head injury that may have had sufficient effect to prevent her from releasing her safety harness. The examination established that the passenger died as a result of drowning. The flexing of the cabin roof occurred above the seating position of the passenger who was trapped in the helicopter. It is possible that the roof flexed sufficiently to cause the head injury to that passenger.

Company ground staff who worked at Green Island conducted a safety briefing (in Japanese) for the passengers. Those staff had completed proficiency testing in emergency procedures applicable to Bell 206 helicopters. The operation of the life jackets, seat belts, and emergency exit procedures was demonstrated. The information was summarised on safety information cards (in English and Japanese) in the helicopter. Each passenger wore a life jacket contained in a belt-mounted bag.

The pilot said that, after the cabin filled with water, he was able to easily egress from the helicopter. When he surfaced, he saw 2 or 3 passengers on the opposite (left) side of the upturned fuselage. He dived and attempted to open the passenger door on the right side of the helicopter but was unable to do so. When he next surfaced, there were 5 passengers on the surface. He made a number of further attempts to open the right side door but could not. Two passengers had made a few dives from the opposite side of the helicopter and they brought the injured passenger to the surface.

The pilot reported that, during an earlier positioning flight to The Pier, the airspeed indicator (ASI) was not functioning normally in that it did not indicate above 40 kts. He thought that the fault was probably due to water in the pitot-static system and expected it to clear during the flight to Green Island. However, the fault remained. After landing at Green Island, the pilot sucked then blew into the pitot head in an attempt to remove any blockage that might be in the system. Because there were no maintenance facilities on the island, there was no means of assessing the serviceability of the instrument before the subsequent flight. The ASI did not function during the accident flight. The pilot said that he relied on the ground speed display on the GPS for speed information during the flight. He did not consider that this had any meaningful affect on his cockpit workload during the flight.

The opinion of other experienced helicopter pilots spoken to during the investigation was that the absence of an ASI would have increased the pilot's workload, particularly in view of the weather conditions. The erroneous indication on the ASI and the need to refer to the GPS display would have disrupted the pilot's normal instrument scan pattern. Further, the GPS displayed ground speed, not "airspeed", so the speed information the pilot was receiving was not appropriate to some flight regimes. Civil Aviation Order Part 20, Section 18 specifies that, for VFR charter operations, a helicopter must be equipped with a serviceable ASI prior to take-off.

The company advised that periods of poor weather usually generated higher demand for helicopter flights because rough seas and/or rain discouraged some tourists from returning to Cairns by boat. The pilot indicated that the company expected the pilots to "give it a go" in the case of bad weather. The company indicated that pilots were expected to "have a good look before turning back" during operations away from the departure area, but that there was no pressure placed on pilots to complete flights in unsuitable weather conditions.

The pilot was programmed to conduct a number of other flights later in the day. However, he stated that the schedule had no bearing on his decision to depart Green Island. The pilot reported that the usual routes from Green Island to Cairns were via the shipping channel, or coastal via False Cape. Wind from the south or south-east at about 15 knots or greater caused mechanical turbulence in the lee of the high terrain on the southern side of Trinity Inlet. Under such conditions he usually avoided the False Cape/coastal route because of passenger comfort considerations. The accident flight was one such instance.

The pilot said that when he departed Green Island, the weather conditions easily met the VFR criteria. His technique in conditions of deteriorating visibility was to descend, maintain a visual reference outside the cockpit and to reduce speed. He applied this technique on the accident flight. Although visibility was poor, he continued, in part because of his experience in operating in similar conditions, but also because the advice from the controller indicated that the weather would improve as he neared Cairns. However, the pilot emphasised that he had turned back on a number of previous occasions because of unsuitable weather conditions.

The pilot stated that, even though he held a night VFR rating it was not current. In addition, he disliked instrument flight and had undertaken minimal instrument flying since achieving the rating in 1992. In any event, the helicopter was not certified for IFR flight. Against this background, he did not consider turning at low level to fly back towards better conditions as a safe option.

The pilot reported that the visibility conditions during the return flight from Green Island were the worst that he had experienced. The sea surface became flat and featureless and blended completely with the precipitation. By that time, it was too late to turn around. He reflected that he might have been better placed by tracking coastal because vegetation and other land features would have provided a higher level of visual contrast against the rain/cloud and may have enabled him to safely continue the flight. Alternatively, he would have been able to land the helicopter and await passage of the weather.

The aerodrome controller activated the Cairns Airport Emergency Plan at 1147 after the helicopter disappeared from radar and the pilot did not respond to radio calls. The police, ambulance, Queensland Emergency Service (QES) helicopter, and Cairns Aviation Rescue and Fire Fighting (ARFF) unit responded. The ARFF response involved dispatching a vehicle towing a trailer mounted rescue boat to Marlin Marina boat ramp, near The Pier. The vehicle arrived at the boat ramp at 1204 and the boat reached the crash scene at 1209. By that time, a tourist vessel and a seaplane were in attendance and the QES helicopter was overhead. All persons involved in the accident were placed aboard the tourist vessel and taken to the Marlin Marina boat ramp. The ARFF later commented that had a launching facility been available at the Barron River adjacent to the airport, they would have arrived on the scene much quicker.

On 19 February 1999, while on the tarmac at Townsville with the auxiliary power unit (APU) operating, the crew of A320 Airbus VH-HYT observed an advisory message for "oil quantity below 1/4" on the electronic centralised aircraft monitoring (ECAM) cockpit display. The limitations section of the operator's A320 Operating Manual stated that the minimum before start APU oil quantity was 1/4. However, it also noted that with the ECAM low oil level message displayed, the APU should be considered unserviceable until an engineering inspection was conducted. This included a check of the APU oil level and inspection of the APU compartment and air intake for oil contamination.

The pilot in command notified the operator's Townsville maintenance engineer of the ECAM APU oil quantity message. The operator's procedure in response to a low APU oil quantity ECAM advisory message required that the APU be inspected for gross oil leaks and that the aircraft maintenance log APU oil servicing records be reviewed to determine oil consumption. However, because the APU bay was a controlled fire zone, the operator's maintenance procedures specified that the APU access door not be opened while the unit was operating.

The engineer opened the APU bay access door and inspected the operating APU for oil leaks. He then returned to the cockpit, where he consulted the aircraft maintenance log to review the APU oil servicing records. Noting that oil had not recently been added to the APU, the engineer advised the pilot in command that he would replenish the APU oil.

Passengers were already on board for the flight to Brisbane. Because of the prevailing hot and humid conditions, the engineer decided that, for reasons of passenger comfort, he would leave the APU running while he replenished the oil. This decision to add oil to the APU while it remained operating was in violation of the operator's standard policy and procedures, which stated that replenishment of APU oil may only be carried out while the unit is not operating.

The engineer connected the oil supply line from a mobile oil dolly to the operating APU. The oil dolly was equipped with a pressurised supply tank, with delivery of oil from the tank being controlled by a hand-operated spool valve in the oil delivery line. The engineer had determined that 1 L of oil should be added to the APU, and he calculated that it would take 15 seconds to deliver that quantity from the oil dolly into the APU. After the oil had been added, the engineer returned to the cockpit to observe whether the ECAM advisory message had extinguished, leaving the APU access hatch open and the oil delivery line still connected to the operating APU. The ECAM advisory remained illuminated, so the engineer returned to the APU bay. As he was climbing onto the workstand, a fire broke out in the APU tailpipe and the APU shut down.

The surface movement controller in the control tower observed fire and smoke coming from the tail of HYT. He sounded the crash alarm and radioed HYT on the surface movement control frequency, but there was no response. Three fire trucks responded immediately and parked in a fanned position around the aircraft's tail, with one truck being parked under the APU exhaust. Two firemen climbed onto the top of that truck to better observe the source of the fire and to determine the appropriate fire-fighting measures to be employed.

The crew had been conducting pre-flight checks when they noticed the APU shutdown. At the same time, they heard the sirens from the fire trucks, and a customer service officer entered the cockpit and notified the crew that the APU was on fire. However, the engineer also entered the cockpit and stated that the fire was under control, but he did not inform the pilot in command that the fire was located in the APU tailpipe and not in the APU bay.

HYT was equipped with a fire and overheat detection system located in the APU compartment. The system was designed to provide for automatic APU shutdown and agent discharge in the event of fire or overheat in the APU compartment while the aircraft was on the ground. A fire warning light was fitted to the overhead panel in the cockpit to alert the crew in the event of an APU fire. However, because the fire was located in the APU tailpipe, it did not activate the APU fire detection system and consequently there was no fire warning. After being advised that an APU fire had occurred, the pilot in command elected to leave the aircraft to obtain further information about the nature of the problem and its effect on the safety of the aircraft. Before leaving the cockpit, he made a public address to the passengers to advise that the aircraft had experienced a problem with its air-conditioning system, and that this would delay the aircraft's departure.

The pilot in command then left HYT through the left forward cabin door (L1) but did not brief the cabin manager, who was stationed at L1, about the nature of the problem. The cabin manager was therefore unable to plan for the possible evacuation of passengers from the aircraft. The pilot in command proceeded to the rear of HYT, where one of the fire crew informed him that the fire was still burning. The fire crew were unaware that passengers were already on board and when the pilot in command asked if they wanted the passengers off the aircraft, the fire controller instructed the pilot in command to disembark the passengers immediately. However, no instruction was given regarding doors that were not to be used for the disembarkation.

The pilot in command then ran back and instructed the cabin manager stationed at door L1 to disembark the passengers. Up until that point, the only information that the cabin manager had been given about the fire was from the customer service officer when the officer had entered the aircraft to advise the pilots of the problem. None of the other flight attendants were aware of the situation until the order to disembark the passengers was given. All passengers and crew were then disembarked through both the front and rear entry doors on the left side of HYT.

The airport fire crew discharged three 5 kg carbon dioxide bottles into the APU exhaust and the fire was extinguished. When the fire controller determined that HYT was safe, he released it to the crew. The engineer conducted a damage inspection of the aircraft and it was dispatched with the APU inoperative.

On arrival at Brisbane, the pilot in command lodged a general flight report stating that HYT had sustained an APU tailpipe fire at Townsville. The report noted that there was no fire warning or ECAM display associated with the APU tailpipe fire. The same day, the engineer reported to the operator's Melbourne maintenance base that HYT had sustained an APU tailpipe fire. Neither of these reports mentioned that the APU oil had been replenished while the unit was operating.

On 4 March 1999, the engineer lodged an accident/injury report of the event with the operator, noting that an APU tailpipe fire had occurred. On 5 March 1999, BASI received an air safety incident report from the company concerning the occurrence and on 8 March 1999, BASI also received an air safety occurrence report from RAAF Townsville.

On 10 March 1999, the operator interviewed the engineer. During the interview, it was established for the first time that the APU oil had been replenished while the unit was operating. The engineer advised the operator that on 21 February 1999, he and another engineer had inspected the spool valve of the oil dolly. The inspection was conducted to determine if oil continued to flow from the delivery hose with the spool valve in the closed position. The inspection revealed that the spool valve was faulty and that it had probably been faulty at the time of the occurrence.

Sequence of events

A Grob Twin Astir two-seat glider, was being towed aloft by a Piper Pawnee aircraft for a passenger flight from Waikerie SA. The pilot was seated in the rear of the tandem cockpit. Several other gliders were airborne in the area, including a single-seat Grob Astir CS that had been launched from Waikerie just over an hour earlier for a local flight.

The pilot of the Twin Astir reported that the flight had been normal following the take-off from runway 26. The tow combination had turned left shortly after becoming airborne and continued climbing in a wide arc. Three km south of the airfield, as the towing combination was climbing through approximately 1,500 ft on a northwesterly heading, he saw a single-seat Astir CS glider near his right wingtip. He estimated that it was 8 to 10 metres away, on a converging course with the towing combination, and travelling at a slightly faster speed. He expected the pilot of the Astir CS to turn right, away from the towing combination. When this did not occur he broadcast a warning "Break right, break right" on the common traffic advisory frequency (CTAF) in an attempt to warn the other pilot. However, when he saw the Astir CS commence a gentle turn left, and a collision seemed imminent, he released the towline. He estimated the time from when he first saw the Astir CS until towline release was 4 to 5 seconds.

The passenger in the front seat of the Twin Astir recalled seeing another glider out to the left and above the towing combination shortly before the collision occurred. It was flying in the opposite direction but not close enough to cause him concern about a risk of collision. His attention was then drawn to the glider off the right wingtip when he heard the pilot broadcast the radio warning.

The Astir CS struck the towline approximately midway between the Pawnee and the Twin Astir, catapulting it into collision with the Pawnee. The collision dislodged the tail of the glider and damaged the left wing of the Pawnee. Witnesses at the airfield, who heard the sound of the collision, saw the Astir CS descend almost vertically. They described the Pawnee's descent as a spin or spiral, completing at least one and a half rotations to the left before it disappeared from view. The pilot of the Twin Astir took avoiding action and returned safely to Waikerie. The wreckage of the Pawnee and the Astir CS were found in a field about 3 km south of the airfield. Neither occupant of the two aircraft survived the collision and subsequent ground impact. The investigation did not find any pre-existing defect with either aircraft that could have contributed to the collision.

Witnesses reported the weather was clear apart from isolated patches of rain to the north of the aerodrome. Visibility outside the rain areas was unlimited. Sun glare was reported not to have been a problem at that time of the day because of the high sun angle. Turbulence was light in weak thermal convection.

Pilot experience and background

The pilot of the Astir CS was a Japanese national who had arrived in Waikerie a week earlier to further his gliding experience and qualifications. He had received his initial training to solo standard in Japan. In the week before the accident he had received further training at Waikerie during which he had made 14 instructional and familiarisation flights. His instructor reported that he had found it necessary to emphasise the need for the pilot to keep a continuous traffic lookout during those flights. The pilot of the Astir CS was issued with a Gliding Federation of Australia (GFA) validation and allowed to make solo flights. He had, as part of his training, undertaken a briefing and oral test required for the use of glider radio equipment on the CTAF. His examiner for the test was also a Japanese national employed as a gliding instructor by the gliding organisation. The instructor reported that the accident pilot's understanding of the English language would probably not have been sufficient to understand the significance of the unaddressed "Break right, break right" warning broadcast by the pilot of the Twin Astir. The pilot of the Astir CS was reported to have been well rested prior to the day's flying operations. Earlier that day he had completed a short flight in the same aircraft, returning due to the lack of thermal currents. A damaged pair of sunglasses was found in the wreckage of the Astir CS but it could not be determined if they were being worn at the time of the collision.

The pilot of the Pawnee held a Commercial pilot licence and valid Class 1 medical certificate. She had obtained her basic glider-towing permit on 27 November 1998 and had conducted aero towing at Waikerie since, accumulating some 117 hours in aero towing operations. As a prerequisite for aero towing, prospective tug pilots were required to have undertaken gliding training to solo standard. She had completed this training, which included spin recovery techniques. The instructor who carried out that spin training reported she was competent and had displayed sound recovery techniques. She had previously qualified and been certified for solo aerobatic manoeuvres, including spin recoveries, in powered aircraft. On the day of the accident she had completed 8 towing flights before the accident flight.

The pilot of the Twin Astir was appropriately qualified for passenger-carrying flights in gliders. Additionally, he held a Private Pilot's Licence and a valid Class 2 Medical Certificate. He was also qualified to conduct aero towing and had flown an aero tow launch earlier that day.

The investigation did not find any pre-existing medical condition that could have impaired the performance of the three pilots involved in the occurrence.

Radio requirements

The gliding organisation relied extensively on the patronage of overseas pilots. Many of those pilots were from non-English speaking backgrounds. Their English language skills were assessed as part of the requirement for the issue of a Radiotelephone Operators Authorisation. This was a requirement for the use of glider radios on the CTAF. Issue of an authorisation was dependent on a satisfactory oral examination on radio use and knowledge of procedures. This exam was conducted by a GFA Level 1 instructor who held either a radio licence or authorisation.

The CTAF area at Waikerie operated on a frequency of 126.7 MHz and extended from the surface to 3,000 ft above the aerodrome, and to a radius of 5 NM. Within the CTAF area pilots had to use the designated frequency, however outside the CTAF boundary glider pilots could use one of three allocated gliding frequencies. The GFA Manual of Standard Procedures (MOSP) required pilots of radio-equipped gliders to broadcast their intentions before entering the CTAF area or when about to take-off. It also stated that "Radio-equipped gliders must also respond to calls when appropriate when operating within a CTAF area". Other radio calls could be made at the pilot's discretion. The gliding organisation had a local rule that required an additional broadcast to be made on downwind.

Each of the aircraft involved in this occurrence was equipped with a serviceable VHF radio, however impact damage to the radio in the Astir CS made it impossible to determine the frequency selected at the time of the accident. The pilot of the Twin Astir reported that the pilot of the Pawnee had broadcast she was taxiing for aero towing operations from runway 26 before the launch. He did not recall hearing any response from other traffic.

Procedures

The local topography around Waikerie produced favourable soaring conditions to the south of the field. This characteristic was known to both tow pilots and glider pilots and was often exploited by them for gaining altitude. However, this area encroached on the designated left traffic pattern from runway 26 and at times resulted in aero towing aircraft and gliders sharing the same airspace. There was no segregation of gliding and aero towing activity. Aeronautical Information Publication procedures permitted gliders to use thermal lift on the "live" side of the circuit. This was provided that glider pilots monitored the CTAF and maintained adequate separation from other traffic in the circuit area. The local gliding operator discouraged the practice below 1,000 ft above ground level. The GFA Rules of the Air required pilots of gliders to maintain separation from other gliders and from towing combinations by at least 200 feet horizontally and vertically.

Vision

Although the see-and-avoid technique was the primary means of collision avoidance for aircraft operating under visual flight rules (VFR) there were limitations to its effectiveness, even for relatively slow aircraft such as gliders and light aircraft. The slim frontal profile of gliders made them more difficult to see than most powered aircraft. In 1991 the then Bureau of Air Safety Investigation published a research report "Limitations of the See-and-Avoid Principle" which documented the physiological and psychological limitations associated with seeing other aircraft. The report recommended that pilots should be aware of those limitations and not rely entirely upon vision to avoid collisions. In recommending the use of alerted see-and-avoid the report concluded that visual acquisition for collision avoidance should be the last defence in achieving separation.

Chapter 4 of the GFA publication Basic Gliding Knowledge (Fourth Edition) titled "The Development of Effective Lookout" described in detail the visual detection of other aircraft and the limitations of human vision in the airborne environment. It also stressed the need for pilots to ensure there was no other traffic in the airspace before manoeuvring and to avoid allowing one's attention to dwell in the cockpit. It did not mention the use of radio to assist in the detection of other traffic. The pilot of the Astir CS should have been familiar with scanning techniques and traffic lookout taught during his initial training. His subsequent training at Waikerie emphasised the need to continuously maintain a lookout. The Astir CS was fitted with a single-piece canopy that provided the pilot with an unobstructed forward and upward view. Visibility from the cockpit of the Astir CS was better than that from other aircraft whose canopies incorporated a windshield bow.

Survival

The pilot of the Astir CS had been wearing an emergency "slim-pack" type parachute. The gliding organisation required pilots of all single-seat gliders to wear a parachute and to be briefed on the emergency escape procedure. The investigation was unable to determine if the pilot was capable of performing the escape functions to parachute to safety following the collision with the Pawnee. The pilot of the Pawnee was unable to regain control of the damaged aircraft following the collision. Information obtained during the investigation suggested that damage to the Pawnee wing structure would probably have made the aircraft uncontrollable. The pilot of the Pawnee was not equipped with a parachute nor was she required to wear one.

Sequence of events

The pilot of a Beechcraft Sundowner was preparing to depart Hoxton Park Aerodrome for his first solo navigation training exercise. The pilot of a Pitts Special S-2A had flown his aircraft from Bankstown to the training area and then to Hoxton Park to conduct practice circuits before returning to Bankstown.

The Pitts pilot reported broadcasting details of his entry to the Hoxton Park common traffic advisory frequency (CTAF) area when he was 5 NM from Hoxton Park, and when he entered the circuit area on the crosswind leg for runway 34. He also reported that, in order to maintain separation from a preceding aircraft in the circuit, he had reduced speed and followed that aircraft.

Meanwhile, the Sundowner pilot had completed his pre-departure checks in the runup bay. He then taxied his aircraft onto runway 34 and commenced the take-off run. At that time, the Pitts was on final approach. The Pitts pilot reported that during the final approach he had repeatedly lowered the nose of the aircraft for short periods in order to provide a view of the flight path to the runway threshold before committing himself to a landing. The last time he had performed the manoeuvre was about 400 m from the threshold.

As the Sundowner was accelerating along the runway, the Pitts landed on top of it about 80 m from the threshold. Both aircraft became entangled and travelled approximately 100 m along the runway before slewing to the right then turning sharply left and coming to rest on the runway. The propeller of the Pitts deeply penetrated the Sundowner cabin and killed the pilot.

Another pilot operating in the circuit heard the Sundowner pilot make a pre-taxiing radio broadcast on the CTAF. The investigation could not establish if the Sundowner pilot made any further broadcasts before the collision. The Pitts pilot later stated that he did not remember hearing any radio transmissions from other aircraft. Further, he reported that he had no idea that he had collided with another aircraft until he vacated the cockpit.

Shortly before the accident, three other aircraft were operating in the circuit area. Their crews later reported hearing each other's radio traffic on the CTAF, but not hearing any radio transmissions from the Pitts.

Wreckage examination

The Sundowner came to rest on a southerly heading, sustaining deep propeller slashes to the left forward side of the cabin. The fin was severed. The Pitts's right main wheel had penetrated the Sundowner's left rear cabin. The very high frequency (VHF) transceiver was tuned to 127.0 MHz, the CTAF, and later testing showed that the radio was serviceable.

The wreckage examination indicated that the Sundowner was serviceable before impact.

The Pitts came to rest on a heading slightly east of south. Both right wings were detached and displaced 90 degrees rearward. The VHF transceiver was tuned to 127.0 MHz and later testing showed that the radio was serviceable. Test running of the engine showed that it should have performed normally before the impact.

The wreckage examination indicated that the Pitts was serviceable before impact.

Pilot information

The Sundowner pilot was 70 years old and held a student pilot licence (aeroplanes) and a valid Class 2 medical certificate with a requirement to wear vision correction. At the time of the accident he was wearing multi-focal prescription spectacles, that corrected his vision to 6/6. He had a total of 106 hours flying experience, including 22 hours on type. He had completed a short dual check flight earlier in the day, and had been cleared to carry out the solo navigation exercise.

Autopsy and toxicological tests did not reveal any pre-existing medical conditions, alcohol or other drugs that might have prevented the pilot from safely operating the aircraft.

The pilot's yellow-brown tinted lens spectacle lenses were designed to change colour in accordance with variations in temperature and ultra-violet light exposure. (As temperature reduced and/or the level of ultra-violet light increased, the lens darkened.) This tint reduced light to the eye and changed the colour of the environment. When viewed through the lens, the contrast between the yellow painted Pitts and the blue sky would have been reduced.

The Pitts pilot was 72 years old and held a private pilot licence (aeroplanes) and a valid Class 2 medical certificate with a requirement to wear vision correction. At the time of the accident he was wearing vision-correcting prescription sunglasses. He had been a pilot for about 38 years, and had about 2,700 hours flying experience, including 491 hours on type.

Weather

The weather at the time of the accident was fine, with visibility of 40 km and scattered cumulus clouds with a base of 4,500 ft above mean sea level. Wind conditions were light and favoured landings on runway 34.

Aerodrome information

Hoxton Park was designated as a CTAF aerodrome. The radio frequency for aircraft-to-aircraft communication was 127.0 MHz. The only mandatory radio broadcasts required in accordance with CTAF procedures were to be made when beginning to taxi and when inbound to the aerodrome. Pilots operating within CTAFs would normally be expected, upon hearing one of those broadcasts, to respond with information on their position and intentions and to arrange mutual separation.

According to the Aeronautical Information Publication, "Enroute Supplement Australia" (ERSA), runway 34 was the preferred runway for use in still wind conditions. Aircraft using runway 34 normally conducted left circuits, resulting in traffic on the downwind leg passing behind aircraft in the runup bay for runway 34. A copes of trees about 10 m in height was located immediately to the south-west of the runup bay. The trees obscured the view that pilots in the runup bay would have had of aircraft on the left base leg or of aircraft turning onto final approach for a landing on runway 34. However, from the holding point on the taxiway between the runup bay and the runway 34 threshold, and from most of the taxiway, the view of traffic on final approach was unobstructed.

The Hoxton Park CTAF was changed from 118.1 MHz to 127.0 MHz with effect from 3 December 1998. Notice to Airmen (NOTAM) C9/98 (10 November 1998) publicised the change, but it was not published in ERSA until the 25 March 1999 issue.

The Robinson R22 helicopter was sent to Fossil Downs Station by the operator to conduct a small mustering assignment. As the operator's pilot was relatively inexperienced and not qualified to conduct mustering operations, the helicopter was fitted with dual controls so that an experienced and qualified pilot who was on-site could conduct the flying while the operator's pilot occupied the other seat. However, after the aircraft arrived at the station, the on-site pilot requested that the operator's pilot transport two passengers from the station to Fitzroy Crossing. Although the operator's pilot had insufficient hours to conduct mustering, he held a commercial pilot's licence and was qualified to carry passengers.

The pilot transported the first passenger from the helicopter landing site without incident. However, during the second departure, at about 15 ft and just as the helicopter was achieving translational lift, it sank back towards the ground. When the pilot increased the collective pitch in an attempt to regain the required departure profile, the low rotor RPM warning horn sounded and the rate of descent increased. The pilot reported that he checked that the throttle was fully open but the main rotor RPM continued to decay. The helicopter landed heavily and the main rotor blades clipped a tree. The pilot reported that as soon as it landed, he shut the engine down. The helicopter was extensively damaged but neither occupant was injured. The pilot reported that he flew the second flight's take-off into wind along a similar path to that flown during the previous passenger flight.

The maintenance organisation that repaired the helicopter reported that no mechanical fault was found that would have contributed to the accident. The accident was not subject to an on-site investigation by the Bureau of Air Safety Investigation.

Weather conditions

The pilot reported that the ambient temperature was about 37 degrees Celsius. He also reported that the humidity was high and increasing as storms were developing in the area. The wind was averaging about 15 kts from the south-east and gusting. The density altitude at the site, without factoring the relative humidity, was calculated to be about 3,000 ft.

The helicopter landing site

The pilot reported that he was using a southerly departure from the site to align with the general wind direction. The pilot reported that in the southerly direction, the helicopter landing site had an available length of about 50 to 60 m from the departure point with about 3 m high bushes at the departure end. There was also a small fence running east to west about 40 m from the departure point.

Helicopter performance

The helicopter weighed close to its maximum all up weight of 622 kgs. The helicopter's flight manual indicated that the calculated maximum weight to hover out of ground effect in nil wind, was about 605 kgs. The pilot did not consult the helicopter's flight manual for likely power requirements and power availability; nor did he conduct a power check prior to arriving at the helicopter landing site in order to ascertain the actual power available. While the Robinson R22 Flight Manual provided hover performance data, it did not contain performance data related to the expected climb performance of the helicopter during take-off, or in forward flight. The operator's operations manual did not provide guidance regarding power margins. There was no requirement under the existing regulations for information or guidance related to required power margins for departure or climb performance to be provided by either the helicopter's manufacturer or operator.

The pilot reported that the power setting required to hover the helicopter in ground effect was about 23 inches manifold air pressure, which was approximately the placarded limit manifold air pressure of 23.5 inches. The pilot could not recall the power indication during the accident take-off.

Ambient wind conditions can have significant and differing effects on a tail rotor equipped helicopter's performance. Engine power is delivered to a transmission system, which drives the main and tail rotors The power required to drive the transmission system is determined primarily by the amount of drag being produced by the rotors and the power available is determined by the power output of the engine(s). The difference between the power available and power required is known as the power margin. If the power required to drive transmission exceeds the amount of power available from the engine, then the main and tail rotor speed will decay, or droop. When the speed of the main rotor droops significantly, the main rotor loses lift and the helicopter descends. Wind blowing over a main rotor provides translational lift that can significantly reduce the power required to drive the helicopter's transmission system. Wind may also assist a helicopter to maintain heading, which also reduces the load demand on the transmission and therefore reduces the power required to drive the transmission. Conversely, a wind from an adverse direction may increase the load demand on the transmission and, in turn, the power required from the engine. Therefore, the wind may cause a net effect which, depending on its strength and direction, will reduce or increase the power required for a tail rotor equipped helicopter to maintain flight.

The density of air is affected by a number of factors including its moisture content. Relative humidity is the ratio of the amount of moisture in the air to the amount it is capable of absorbing at a given temperature. The greatest decrease in air density (increase in density altitude) due to moisture content will be at a high temperature. In general, as the density altitude increases, helicopter rotor and piston engine performance decrease. The performance data provided in the R22 helicopter's flight manual is only valid for nil-wind conditions and does not account for the adverse effects of high relative humidity.

Although the Civil Aviation Orders (CAOs) specify minimum performance requirements for single and multi-engine aeroplanes, there are no minimum performance criteria specified for helicopters.

Pilot Experience

The pilot had about 173 hours flying experience, of which about 83 hours were in command. All his flying experience had been gained on the Robinson R22 helicopter. Prior to joining the operator, he had flown about 14 hours during the 15 months since gaining his commercial (helicopter) pilot's licence in September 1997. He had been employed by the operator for less than one month and had accumulated just over 36 flying hours in that time. His initial training was conducted at several helicopter training schools in Queensland, and he reported that during the training, he had not experienced the helicopter being close to limits of power or practiced rejected departures and had not previously experienced main rotor RPM droop. He also reported that at the time of the accident, he was unaware of how to recover from a low rotor RPM condition. There were no available records related to his initial flying training, however, the pilot reported that he considered the training to be adequate. The operator conducted a proficiency check on the pilot about three weeks prior to the accident. The pilot's performance during the check was rated as satisfactory. About a month after the accident, the pilot attended a Robinson Safety Course where he flew with an experienced R22 helicopter instructor. The instructor reported that the pilot demonstrated an inappropriate take-off technique and that he required remedial instruction.

The Civil Aviation Orders impose a minimum requirement of 100 hrs as pilot-in-command before a pilot may conduct mustering operations. The Civil Aviation Regulations specify that a pilot may obtain a commercial (helicopter) pilot's licence, under certain circumstances, after a minimum total of 105 flying hours of which at least 35 hours are as pilot-in-command.

The company's operations manual required pilots to obtain authorisation from the Chief Pilot or a person nominated by the Chief Pilot before conducting any flights. The pilot reported that the Chief Pilot told him that the on-site pilot was "in charge". When he was requested to conduct the passenger flights, the pilot believed that the on-site pilot had the appropriate authority.

History of the Flight

The Agusta /Bell 47G-2A1 helicopter, registered VH-FLI, was borrowed by the pilot to fly his sister to her wedding at the family property near Holbrook NSW.

The pilot arrived at the helicopter owner's property around 0900 Eastern Standard Time on the day of the accident, and with assistance from the owner, he completed a pre-flight inspection of the helicopter. The pilot subsequently conducted a number of flights on the day of the accident.

At about 1730, the pilot and his sister boarded the helicopter and departed in an easterly direction. The pilot then followed a route that ran adjacent to the Holbrook to Jingellic road in order to remain near the car being driven by his mother.

Witnesses reported that the helicopter was flying at a very low height as it neared Chinamans Gap. At approximately 1745, when the helicopter was about 6 km from its destination, it struck a powerline, pitched nose down and impacted the ground on its left side. The impact and the subsequent fire fatally injured the occupants and destroyed the helicopter.

Pilot Information

The pilot held a Commercial Pilot Helicopter licence, issued in September 1993. The pilot's Bell 47 qualification had been gained in August of that year. The pilot had also served as a helicopter pilot in the Royal Navy, the Australian Army, and the Royal Australian Navy. His military pilot logbooks indicated that he had significant helicopter low-level flying experience and his civilian logbook showed that he had completed civilian helicopter low flying training. As part of that training he had been alerted to the dangers of powerlines during low-level flight, and of the need to carry out a reconnaissance of an area before conducting a low-level flight. The pilot had not previously flown the route followed to the property where the wedding was to be held.

Records of his Bell 47 flying experience were incomplete, with the last recorded flight being in August 1994. However, witnesses reported that he had flown this Bell 47 on numerous occasions since that time. The pilot's total recorded Bell 47 flying time was 23.8 hours. His friends and colleagues indicated that he was a careful pilot.

While the pilot was required by the Civil Aviation Safety Authority to have "visual correction for distant vision" during commercial flights, his uncorrected vision was adequate to meet the private pilot licence standard. No evidence was found that the pilot was wearing spectacles at the time of the accident. Witnesses indicated that the pilot had received adequate rest prior to the flight. There was no evidence found to indicate that the pilot's performance was adversely affected by any pre-existing physiological condition.

Wreckage Information

Examination of the wreckage indicated that the powerline first entered the area between the skid landing gear and the cockpit floor, severing the landing light before contacting the landing gear forward cross tube. The main-rotor blades severed the tailboom approximately 1 m forward of the tail rotor assembly. The two fuel tanks, which had detached during the initial impact, burst open. The main wreckage of the helicopter was subjected to an intense fire fed by the fuel from the burst tanks.

Examination of the wreckage revealed no mechanical faults that may have contributed to the accident. No wire-strike protection devices were fitted to the helicopter.

Weather

The wind was light and variable, visibility was 40 km, and there was 1 to 2 octas of high-level cloud. The temperature was 29 degrees Celsius, the dew point was 2 degrees Celsius and the QNH was 1012hPa. The likelihood of carburettor icing at the time of the accident was extremely low. The sun was behind the helicopter at the time of the accident.

Accident Site

The helicopter had impacted the tarmac road surface, just beyond a road cutting in a ridgeline. The powerline ran approximately 90 degrees to the helicopter's flight path and was strung between two poles that were each located on peaks of the ridge. The distance between the two poles supporting the powerline cables was about 900 m. At the point where the helicopter contacted the powerline cables, the cables were at a height above the roadway of approximately 31 m. The powerline had been erected several years before the accident and had developed a dull oxidised finish. There were no high visibility devices on the powerline cables to make them easier to detect from aircraft. No maps were found with the wreckage, and due to the relative recency of the erection of the powerline they did not appear on topographic maps of the area.

Pilots who regularly flew in the area indicated that the powerline was difficult to see from the air because the cables blended with the background of trees and other vegetation. One pilot advised that he had previously reported this to the power transmission company, suggesting that the powerline cables were a hazard to aircraft and that something should be done about making them more visible. The power transmission company reportedly replied that the height of the powerline was lower than the minimum height for powerlines requiring the fitment of high visibility devices as laid down in Australian standards.

Regulations and Standards

The Australian standard relating to cables and their supporting structures, required them to be marked with warning markers if the height of the lines exceeded 90 m above ground level. There was, however, a proviso that this standard could be varied if an air operator referred the matter to the appropriate Regional Airspace Advisory Committee for resolution.

The Civil Aviation Regulations require a helicopter that is not over a town or populous area, to remain a minimum of 500 ft above ground level. Further, the helicopter must be 500 ft above any obstacle within a 300 m radius of the helicopter's flight path, unless taking-off or landing.

A de Havilland Canada DHC-8, VH-TQT, was inbound to Mildura from Melbourne and overflew a glider that was crossing from left to right. At the time, TQT was descending through 7,300 ft and the crew had made inbound and top of descent broadcasts. The aircraft, which were outside controlled airspace, passed within an estimated 30 to 60 m. VH-TQT was on the area frequency 122.1 MHz and the glider, VH-GDJ, was on the glider frequency 122.7 MHz.

AIP Australia ENR 5.5, paragraph 1.1.3, states: "Except for operations in controlled airspace, gliding operations may be conducted no-radio, or may be on frequencies 122.5MHZ, 122.7MHZ or 122.9MHZ, which have been allocated for use by gliders. Unless otherwise authorised, gliding operations in controlled airspace must be conducted using the appropriate air traffic control frequency. Radio equipped gliders at non-controlled aerodromes will use the MBZ frequency or CTAF. Whenever possible, when operating above 5,000 ft AMSL outside a MBZ or CTAF area, glider pilots are expected to listen out on the area VHF and announce if in potential conflict."

Consequently, in the circumstances of this occurrence, the glider pilot was "expected to listen out on the area VHF" but was not required to do so.

The pilots of both aircraft advised that, from the time of sighting of the other aircraft, they had no time to take avoiding action.