At 2015 hours on 24 May 1993 PH-BFA, a Boeing 747-400 aircraft, was hearing touchdown on runway 07 at Sydney (Kingsford Smith) Airport, having received a clearance to land from air traffic control. At the same time, a Federal Airports Corporation safety vehicle, Car 9, was conducting a search for reported debris on a portion of taxiway 'A' near runway 07.

During the search, the vehicle crossed the taxi holding position markings and entered the 07 runway strip. The crew of PH-BFA observed this incursion and carried out a go-around manoeuvre from a low altitude. It was determined that the safety officer in Car 9 had inadvertently crossed the holding point as a result of not seeing the holding point lighting/markings provided at the intersection of taxiway 'A' and runway 07.

Prior to commencing the Night VFR (Visual Flight Rules) flight, the pilot obtained a pre-flight briefing by facsimile.  This briefing included the appropriate weather forecast for the intended route.

After departing Coolangatta, the pilot reported to Brisbane Flight Service that he intended climbing to 7,500 ft and that he would remain outside controlled airspace. About 22 minutes later a single radio transmission was received by Brisbane Flight Service.  The transmission, by a male voice, said 'I'm doing cartwheels'.  This voice was different from the voice that made the initial transmission from VH-IWJ to Flight Service.

Witnesses in the Evans Head area observed the aircraft flying towards the north-west at an estimated altitude of 1,000 ft above the ground.  They reported that it was flying erratically before commencing a looping manoeuvre.  At the top of that manoeuvre the aircraft appeared to lose all airspeed, then dive vertically into the ground.

The aircraft was extensively damaged by impact forces.  Inspection of the wreckage did not reveal any pre-existing faults that may have contributed to the occurrence.

Post-mortem examination of the pilot did not provide evidence sufficient to determine whether he had suffered from any form of incapacitation.

The weather forecast obtained by the pilot indicated that showers were expected along the route and that some low cloud would be associated with the showers.  Provided the pilot remained clear of the showers a flight under VFR should have been possible.  There is extensive ground lighting in the area from Coolangatta to Ballina but after that the ground lighting reduces as the settlements become more widely spread.  The moon was located in the western sky, but most witnesses reported that it was dark at the time they observed the aircraft and that there was cloud in the area. Consequently, the pilot may have been deprived of a visual horizon from time to time.

The pilot was reported to have been in current flying practice, having last flown at night on 28 February 1993.  He had held a Night VFR rating since 25 September 1987.

The available evidence is consistent with the pilot having lost control of the aircraft and being unable to regain control before it impacted the ground.

SIGNIFICANT FACTORS

The factors leading to an apparent loss of control of the aircraft could not be positively determined.

The aircraft took off from the strip near the homestead at about 0645 hours to conduct cattle spotting operations. At about 0930 hours, the pilot reported by radio that he had completed the spotting task and was directed by the property manager to fly to the western section of the property and check the status of three bores. When the manager arrived back at the homestead at about 1200 hours, he found that the aircraft had not returned. Search arrangements were initiated and the wreckage of the aircraft was later found approximately one kilometre from the second in the series of bores to be checked. There were no witnesses to the accident.

On-site investigation revealed that the aircraft had crashed on flat, open terrain while heading in a north-easterly direction. The aircraft initially contacted the ground with the left wingtip followed by the propeller 14 metres beyond this point. There was evidence of a flash fire at this location, and of the aircraft then cartwheeling, before coming to rest 60 metres from the initial impact point. The relationship between the wingtip ground impact mark and the propeller impact point suggested that, at initial impact, the aircraft was in a slightly nose down attitude and banked steeply to the left.

The aircraft was severely damaged by a combination of impact forces and post impact fire. Examination of the wreckage did not disclose any condition or fault which might have contributed to the accident, although fire damage precluded a complete examination of some components, particularly the instruments and controls in the cockpit area.

The weather in the area around the time of the accident was reported to have been fine and hot with a light and variable wind. There were no restrictions to visibility. Flying conditions as described by occupants of the search aircraft were good with only light turbulence.

The broader area over which the aircraft was operating was covered with lush knee-high grass. Advice from the Bureau of Meteorology indicated that the chances of a dust devil (willy-willy) forming in these conditions were very small. Dust devil formation usually required barren, very hot and very dry conditions. No dust devils were observed in the area during the on-site phase of the investigation.

Considerable bird activity was noted around bores on the property. However, no evidence of the aircraft having struck a bird was found, although the post-crash fire could have destroyed any bird remains which might have entered the cabin area.

The notepad apparently used by the pilot to record information on each bore was found along the wreckage trail. Writing in pencil on the notepad indicated that the pilot had inspected the first bore (D-15) and recorded his observations. Beneath this writing was an incomplete recording of information on the second bore (X-8). At the end of this writing was a pencil mark similar to that which might be expected if the writing platform or the pencil was bumped or disturbed.

Bore inspections were a regular aspect of the pilot's flying duties. Inspections involved flying over the bore and checking the amount of water in the holding tank along with the condition of the adjacent animal drinking trough. The task could be readily accomplished from a flying height of 500 feet above ground level.

There was no indication of any physiological or psychological condition which might have affected the pilot's ability to operate the aircraft. He had been flying in the area for some 14 months during which time he had conducted many bore inspection flights. The pilot completed a course in low flying in January 1993.

Factors

The factors which contributed to this accident could not be determined.

The helicopter had been hired by the pilot to take family members on scenic flights in the local area. It was observed operating at low level between Tacoma and the F3 freeway during the afternoon. During its fourth flight it was observed flying low over the F3 freeway on a southerly heading then make a rapid 180 degree turn onto a northerly heading which it maintained for a short time. The helicopter then turned to the east and descended into a shallow depression where it collided with high tension power lines some 47 feet above ground level.

The high tension power lines span a depression on the eastern side of the F3 freeway. The wires are suspended between poles which are masked by trees on their western sides and are hidden from view when approached from the west at low level. The wire spans blend with the background vegetation. As the helicopter was approaching the wires from the west at low altitude it is probable that the pilot did not see the wires in time to avoid collision. The reason why the pilot was operating at that height at the time of the accident was not determined.

Investigation did not reveal any mechanical deficiencies with the helicopter which may have contributed to the accident.

Significant Factors

• The helicopter was operating at a very low height.
• The high-tension power lines are difficult to see when approached from the west at low level.

The aircraft was conducting cotton spraying operations on a 61 hectare field. The pilot stated that he had completed numerous swath runs, using a human marker for guidance, when it became necessary to fly beneath power lines converging at the southern corner of the field. He then completed a pass under the power lines in a south easterly direction and carried out an extended procedure turn to facilitate the next pass under the wires. He said he could then see the marker moving off to the next swath position.

The aircraft was positioned to pass beneath the powerlines at a speed of about 100 knots with a power pole to the right and the marker to the left, and moving left. As the pilot passed the power pole he heard a loud thudding noise, associated with a left yaw. The pilot said that he thought at the time he had clipped the power pole, but as he regained control of the aircraft, he noticed the left wing was damaged. Shortly after, he noticed the marker lying in an irrigation ditch, near where she had been standing. The marker was killed as a result of being struck by the aircraft.

The pilot was mustering cattle. The helicopter's gross weight was estimated at 602 kilograms which was 20 kilograms below maximum allowable. The terrain was approximately 1000 feet above sea level and the outside air temperature was about 25 degrees Celsius.

The surviving passenger recalled that the helicopter was about 35 feet above ground level when he first heard the low rotor warning horn and saw a warning light on the instrument panel. There were trees ahead which were about 25 feet high. The pilot said "whoops", pulled up, nosed over and veered slightly left towards a gap in the trees. At the time the helicopter had very little forward airspeed. He subsequently described a weightless feeling which is consistent with the pilot having applied a large forward cyclic input to achieve the "nose over". He recalled that the pilot was "fighting" the cyclic control for a short time as the helicopter rolled to the right into a tree. The survivor also remembers leaves flying about but he has no recollection of a rotor blade hitting a limb.

Damage sustained by the helicopter indicated that the main rotor struck a tree limb and that one rotor blade was severed about one metre inboard from its tip. When the section of rotor was severed, the remaining rotor blade flapped up causing a severe mast bump which resulted in overload failure of the mast at the main rotor head. The main rotor assembly departed and the unsevered rotor blade impacted the first section of the tail boom immediately aft of the engine. The main rotor did not sever the tail boom or the tail rotor drive shaft or the tail rotor control tube. The tail rotor drive shaft within the tail boom was severed in torsional/bending overload when the boom separated probably as the helicopter impacted the tree and fell through its limbs.

The right side of the helicopter, in the area of the fuel tank to the pilot's upright seat cushion, was pushed inwards probably when the helicopter impacted the tree. The right side of the landing skid was severely deformed and broken. No such damage was found on the left skid. It is probable that, after the tree impact, the helicopter impacted the ground right side low and bounced on to its left side where it was found at rest. There was no post crash fire. Damage to the tail rotor assembly indicated that the tail rotor was still rotating but probably not being driven by the engine when the tail rotor blades impacted foliage.

The helicopter was found with both the drive belts off the pulleys associated with the drive system from the engine to the main gearbox. There was no evidence of previous damage or wear on the drive belts, the pulleys or bearings; nor has any fault been found with the clutch or free wheeling unit. However, marks were found on the inside opposing faces of the flexible coupling between the main gearbox output shaft and the tail rotor drive shaft, forward of the upper pulley assembly. This indicates that the upper pulley assembly had moved forward abruptly thereby misaligning the belts enough for them to jump off the pulleys. There is no known inflight manoeuvre which could compress the forward coupling to the extreme as found. However, a severe tree impact or ground impact could dislodge the upper pulley assembly enough to damage the coupling and cause the belts to come off. It is most likely that the drive belts came off after the initial tree strike by the main rotor and not before. Engineers have found no significant fault with the engine or airframe which might have contributed to the accident. A magnetic particle inspection of engine components proved that the engine had not suffered a significant overspeed.

Subsequent trials in a Robinson R22 helicopter were conducted by a very experienced flying instructor in conditions similar to the day of the accident. His helicopter successfully hovered out of ground effect at 35 feet above the ground with rotor revolutions per minute (RPM) as low as 96% at which time the low rotor RPM horn was audible and the low rotor warning light was illuminated. During a simulated engine failure from a low hover it was noted that the cyclic still responded normally with rotor RPM as low as 75%.

The survivor's description of the accident is consistent with the pilot having inadvertently achieved low rotor RPM, possibly losing height, and trying to recover while avoiding nearby trees. His description suggests that the "nosing over/bunting manoeuvre" managed to unload the main rotor to the extent that tail rotor thrust rolled the helicopter to the right. It is a known fact that a pilot may not be able to counteract this uncommanded roll to the right with left cyclic input. It is probable that an uncommanded roll to the right caused the helicopter to collide with a tree; this is consistent with the survivor's description of the helicopter being "pulled into the tree".

SIGNIFICANT FACTORS

The following factors were considered relevant to the development of the accident:

1. The pilot inadvertently allowed the rotor RPM to decay.

2. During the attempted recovery from low rotor RPM, the pilot's flight control inputs induced an inflight manoeuvre which resulted in an uncommanded roll to the right.

3. The helicopter collided with a tree.

Pilot transmitted a Mayday call stating the aircraft engine had failed 10 miles NW Aurukun and that he was conducting a forced landing into trees. Nothing further was heard from the aircraft, and the burnt-out wreckage was found some hours later in a densely treed, inhospitable area 44 km north of Aurukun.

The investigation determined that the engine fuel mixture control cable end had become detached from the mixture control arm on the fuel control unit. This allowed the control arm to move to the 'idle cut-off' position, causing the engine to fail because of fuel starvation.

The MiG 15UTI, VH-LSN, took off from runway 12 at Canberra Airport with the pilot and one passenger on board. After becoming airborne, the aircraft entered a climbing left turn and levelled at about 1,200 ft above ground level. The pilot advised the tower controller that he was having a minor technical problem and requested a landing. After a short discussion, the aircraft was cleared to land on runway 35. When the aircraft was about 4 km from the threshold of runway 35, it was seen to enter a steep nose-down attitude. The aircraft subsequently impacted the ground, and the pilot and passenger were killed.

The Bureau of Air Safety Investigation determined that an engine over-temperature occurred. The over-temperature was probably associated with an internal failure of the upper of two engine fuel pumps. The resulting excessive turbine temperatures led to the turbine blades creeping and rubbing on the turbine casing, and heat generated in the tail pipe as a result was then transferred into the fuselage area. Fuel in the fuselage area aft of frame 21, probably from a leaking fuel boost pump, was ignited by the high radiated temperatures in the tank bay. The fire melted and burned the rudder and elevator control tubes and control of the aircraft was lost. The area where the fire occurred was not monitored by over-heat or fire detection devices, and the pilot was therefore probably not aware of the fire.

The aircraft had been cleared to track south over water at 1,000 feet through the Coffs Harbour zone. At 1324 hours the pilot reported passing Woolgoolga and subsequently reported abeam the control tower. At this time he requested clearance to descend to 500 feet. He was cleared to descend, but two minutes later, at 1334 hours the pilot reported that he was returning to Coffs Harbour for a landing and that he had lost visual contact with the water. He was cleared to join the circuit on downwind for runway 21 on a visual approach and was asked to report abeam the control tower. This was acknowledged by the pilot at 1334:51, but there was no further communication from the aircraft. An overflying jet aircraft reported receiving a transmission from a VHF Survival Beacon for a period of about 10 seconds shortly after the time of the pilot's last transmission.

The Automatic Terminal Information Service (ATIS) was reporting 3 octa of cloud at 1,000 feet, with lower patches, and 4 octa of cloud at 2,000 feet. Showers were reported in the area.

The aircraft wreckage was located in the sea near Sawtell. Wreckage examination suggests the aircraft struck the water in a descending right turn. There was no indication that the aircraft was not capable of normal flight immediately prior to the accident. A heavy rainstorm was reported near Sawtell at the time of the accident. The pilot was not qualified for flight in other than visual conditions. It is most probable that the aircraft inadvertently entered a heavy rain shower which deprived the pilot of visual contact with the land and water. The pilot attempted a turn to head back to Coffs Harbour aerodrome but as he was not qualified for flight by sole reference to the aircraft's flight instruments, it is probable the aircraft entered a steep descent from which the pilot was unable to effect a recovery prior to collision with the sea.

Significant Factors

1. The pilot inadvertently flew into conditions of limited visibility associated with a heavy rain shower.

2. The pilot was not qualified for flight by sole reference to the aircraft's flight instruments.

3. The conditions of visibility reduced such that the pilot was unable to continue the flight by visual reference to the land and water.

4. The pilot attempted to turn to regain visual contact and during the turn entered a descent from which he was unable to effect recovery prior to collision with the sea.

The pilot and his wife flew their own aircraft from Bankstown to The Oaks where a set of spark plugs was purchased. As the engine had operated normally during this flight, the pilot declined an offer by the seller to fit the new spark plugs to the engine. Three days earlier an engine ignition system unserviceability was rectified by a licenced aircraft maintenance engineer who replaced two spark plugs.

The aircraft was taxied to the southern end of the airstrip where an engine run up check was carried out prior to take-off. The passenger noted no irregularities during this check.

The take-off was commenced in a northerly direction. After the aircraft became airborne the engine began to run roughly, accompanied by a significant loss of power. The pilot was able to maintain a shallow climb at an indicated airspeed of 45 knots.

After travelling for approximately 1.5 kms in a northerly direction and reaching a height of between 200 and 300 feet, the pilot commenced a level turn to the left. When the aircraft had turned through about 40 degrees the left wing dropped, and the aircraft entered a steep nose down spiral dive. Although rotation ceased, the aircraft struck the ground heavily. The pilot received fatal injuries, and the passenger was seriously injured.

The loss of control occurred at a height insufficient for the pilot to effect a safe recovery.

An examination and testing of the engine and its systems did not reveal the reason for the significant loss of engine power.

Significant Factors

1. Immediately after liftoff, the engine suffered a significant loss of power.

2. The climb performance was substantially reduced.

3. The aircraft stalled during a left turn and entered a spiral dive at an insufficient height to permit recovery.