Loss of control

The aircraft was engaged on an IFR freight operation from Bankstown to Canberra and return. The flight from Bankstown to Canberra was uneventful and the aircraft subsequently departed for Bankstown at 1836 ESuT, carrying about 45 kg of light freight. A flight plan submitted by the pilot indicated the aircraft was to track via Shellys at 7,000 ft, thence to Bankstown outside controlled airspace (OCTA).

The pilot reported to Sydney Flight Service over Shellys at 1900, maintaining 7,000 ft, and estimating Bankstown at 1927. Three minutes later the pilot reported commencing descent, and subsequently reported on descent to Flight Service at 1906 after a frequency change. No further radio transmissions were received from the aircraft. Weather reports indicated that instrument meteorological conditions were prevailing in the area at the time.

The wreckage of the aircraft was located the following afternoon on the eastern slope of Axehead Mountain at an elevation of about 2,145 ft. The damage to the aircraft was consistent with having struck trees at cruising speed in straight and slightly descending flight, on a track of about 2930M. Both fuel tanks were completely disrupted, and the wreckage had been largely incinerated in the subsequent fire.

Later examination of the wreckage indicated the aircraft had been capable of normal operation at the time of the accident.

Recorded radar data showed that at 1906 the aircraft was tracking inbound on the 2200 radial of the Sydney VOR at a range of 50 NM, and passing through an altitude of 5,600 ft. When the aircraft was at a range of about 40 NM from Sydney, at an altitude of about 4,300 ft, it was observed to turn left and take up a track of about 2900, still gradually descending. The aircraft continued to maintain this track for a further 22 NM before it faded from radar. The last recorded altitude was at 2,900 ft. At the time of the accident the aircraft was OCTA and not under radar control. Radar returns from the aircraft transponder were suppressed from radar displays to reduce clutter, in accordance with normal operating procedures.

An examination of the medical history of the pilot showed no evidence of any cardiovascular disease or cerebrovascular disease risk factors. He was aged 49 years and held a current Class 1 medical certificate. An ECG performed at his last medical examination indicated a slight conduction defect, but in the absence of other indications of cardiovascular disease the pilot was assessed as fit.

From the evidence available, the flight path of the aircraft was consistent with the pilot becoming incapacitated as the aircraft descended towards Bankstown. The left turn at 40 NM from Sydney onto a heading of about 2900 is considered to have been unintentional as the subsequent track, which was about 1000 left of the flight planned track, took the descending aircraft towards mountainous terrain which was obscured by low cloud. The final track was not directed to any known tracking aid.

Significant Factor

The pilot probably suffered a sudden incapacitation during flight which rendered him incapable of continuing to safely operate the aircraft.

The purpose of the flight was to conduct an aerial inspection of a corn crop located approximately 1 km east of the airstrip. Witnesses reported seeing the aircraft in straight and level flight at a height of about 500 ft and hearing a change in the engine noise. A short time later, the right wing dropped, and the aircraft entered a steep, nose down, spiral descent which continued to ground impact.

Examination of the accident site showed that the aircraft had struck the ground while inverted and in a steep nose-down attitude while rotating to the right. The nature and extent of damage to the propeller indicated that the engine was developing significant power at impact. Inspection of the wreckage revealed no faults which might have contributed to the accident.

The evidence suggests that the aircraft probably stalled, causing the right wing to drop and a spiral dive to develop from which the pilot was unable to recover in the height available. The reason for the aircraft entering the manoeuvre was not determined.

Factors

1. The aircraft probably stalled, resulting in a spiral dive developing.

2. The pilot was unable to recover the aircraft to normal flight in the height available.

The aircraft was being flown to Coffs Harbour in preparation for an open day, during which the aircraft was to be displayed on the ground and in the air. Witnesses at Ballina observed the aircraft take off and conduct a circuit before flying low along the strip in the take-off direction. The aircraft then pulled up to about 75 degrees nose up, levelled at about 350 ft, and descended again while travelling in the same direction. It then accelerated, turned right, climbed to about 500 ft and departed in the direction of Coffs Harbour.

Witnesses at Coffs Harbour saw the aircraft approach the aerodrome from the west, cross over the main runway, turn right and fly south. The aircraft was then observed to turn north and approach the airfield at low level before abruptly entering a very steep climb. At an altitude estimated by some witnesses as between 200 and 400 ft above ground level, the aircraft rolled right before diving vertically towards the ground and disappearing behind trees. A short time later, the sound of impact was heard, and smoke was seen rising above the trees.

Examination of the accident site revealed that the initial impact occurred when the aircraft struck 8m high trees. This ruptured the right fuel tank, providing the fuel source for the fire. Examination of the burnt-out wreckage indicated that at ground impact, the aircraft was yawing right and skidding left. The aircraft struck the ground with about 7 degrees of left bank, a level nose attitude and low horizontal speed. The engine was operating at low power at the time of impact.

Of the two occupants of the aircraft, one held a commercial pilot's licence and the other a student pilot's licence with passenger carrying approval. Consequently, the latter was not qualified to act as pilot-in-command for the flight from Ballina to Coffs Harbour. It was not possible to establish who was controlling the aircraft at the time of the accident. Both pilots had limited total flying experience, as well as limited experience on the aircraft type.

The investigation concluded that, following the pull-up from about tree height, the aircraft probably stalled and entered an incipient spin to the right. Recovery from the spin was not effected prior to ground impact. The reason for conducting the pull-up manoeuvre was not determined.

FACTORS

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

1. The experience level of both pilots was low.

2. Control of the aircraft was lost at a height insufficient to effect a safe recovery.

The aircraft had been stored in a hangar/shed, in a partially dismantled state for about 4 months. The pilot assembled and rigged the aircraft with the help of a person not familiar with aviation, and without reference to any qualified person or documentation. The pilot then boarded the aircraft, started it, and taxied for take-off. The take-off appeared normal, and the aircraft turned 90 degrees to the right at the upwind end of the runway. During the climb, at about 300 feet above ground level, the aircraft was seen to adopt a steep right wing low attitude and enter a spiral descent to ground impact.

The pilot was rescued from the wreckage and taken to the hospital, where he later died. He was not wearing a helmet during the flight.

Inspection of the wreckage revealed a broken wooden plug in the wing warping rod, where it attaches to the forward part of the right wing. The remains of the plug were found partially withdrawn from the rod end and an inspection of the left wing warping rod revealed the wooden plug partially withdrawn from its rod end by an amount similar to that found in the right wing. Microscopic analysis of the broken plug showed that the plug had been broken prior to the ground impact and that its material, which did not meet the manufacturer's specifications, had also degraded after lengthy exposure to the environment.

The plug failure, alone, should not have resulted in the loss of control of the aircraft. The aircraft is controllable with an adjustment of the position of the controls to compensate for the loss of the warping rod.

No other defects were found in the aircraft which could have contributed to the loss of control and subsequent crash.

The pilot's logbook contained no reference to prior experience in flying the Scout aircraft and indicated that he was inexperienced in operating ultralight aircraft. Anecdotal evidence suggested that he had more total hours than recorded in the logbook and also had some flying experience in the Scout, about two years prior to the crash.

The pilot had been solo-checked eight months prior to the crash and his logbook indicated that he had flown, unsupervised, on many occasions since that flight check, in contravention of the Australian Ultralight Federation Operation Manual requirements.

The wind on the ground at the time of the take-off was westerly at about 5 knots and was likely to have been stronger above tree top level. As the pilot turned away from the take-off strip, he probably would have had a tailwind component.

It is probable that the wooden plug broke after take-off. The pilot lost control following the failure, either because of inexperience, or he was distracted by the failure and allowed the speed to decrease to the stall speed as the aircraft climbed. The rudder is normally used for primary roll control of the Scout and if the pilot had not been aware of this, he may have aggravated the situation by using other recovery techniques.

Safety Actions

The Bureau of Air Safety Investigation has made the following recommendations:

1.  That the Civil Aviation Authority, in consultation with the Australian Ultralight Federation;

i) Advise owners of Wheeler "Scout" Mk3 ultralight aircraft to examine the wing warping control attachments and replace any suspect parts, and ii) As a matter of urgency complete and distribute the AUF Technical Manual.

2. That the Civil Aviation Authority research the wearing of helmets in ultralight operations with the view to determining if regulation in this area is warranted.

3. That the Civil Aviation Authority;

i) Examine its procedures for surveillance of sport aviation groups to ensure that the standards required by the regulations are being met;

ii) Actively pursue breaches of regulations or operating procedures, and, in conjunction with the Australian Ultralight Federation,

iii) Maintain an ongoing education programme of all ultralight operators with regard to their privileges and responsibilities under the Civil Aviation Orders and the AUF Operations Manual.

The following Safety Advisory Notices have been sent to the Australian Ultralight Federation:

1. The Australian Ultralight Federation should consider reminding all ultralight operators of;

i) The dangers associated with substituting substandard parts in their aircraft, and, 

ii) The dangers associated with not maintaining their aircraft to manufacturers' specifications.

2. The Australian Ultralight Federation should emphasise the potential safety benefits in wearing helmets during ultralight operations.

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.

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.

Aerospatiale AS355F1 helicopter VH-NJL was to land on a sports oval as part of a police public relations display for school children. It approached from the north-east and entered a steep descent from about 22 m above ground level. The descent rate was reported to be higher than normal. This high descent rate continued until ground impact. The helicopter bounced and completed two anticlockwise rotations before coming to rest. A small fire, which began in the engine bay, grew to completely destroy the helicopter.

On 1 July 1992, SAAB SF-340A, VH-EKT, was engaged on a scheduled passenger service from Melbourne, Victoria to Devonport, Tasmania. During the flight, the crew experienced difficulty in controlling the right propeller RPM. When the aircraft landed at Devonport, directional control was lost.

The aircraft departed the runway and ran through a ditch in soft, muddy ground. The aircraft sustained substantial damage but there were no injuries to passengers or crew. The investigation revealed that a severe asymmetric thrust condition developed after landing when reverse thrust was selected but the right propeller remained at a positive blade angle.

The report concludes that the right propeller control unit was defective, due to internal oil leakage across the feathering solenoid valve. As a result, the propeller failed to respond normally to pilot control input.

The pilot departed Moorabbin with one passenger on board and flew to the designated Moorabbin aerobatic training area with the probable intention of practising aerobatic manoeuvres. The pilot was approved to perform aerobatic manoeuvres down to 500 feet. The passenger was an experienced flying instructor who also held an approval for low level aerobatics down to 500 feet, but he was not experienced on the Pitts S2A aircraft.

Only one known witness saw the aircraft in the last few seconds before impact. Her attention was attracted to the aircraft by its loud engine noise. She briefly observed the aircraft performing an aerobatic manoeuvre while descending towards the ground at an angle of about 45 degrees. The aircraft was travelling in a westerly direction when it disappeared behind a row of Cyprus trees and impacted the ground about 300 metres north-west of her location. Subsequently the witness was shown a video of Pitts aircraft performing various aerobatic manoeuvres. The manoeuvre she identified as what she saw VH-SZA perform was a descending snap roll to the left.

Airframe and engine damage indicated that the aircraft was rotating to the left when it impacted the ground in a steep nose down attitude. Propeller damage indicated that the engine was at a low power setting at impact. No fault has been detected with the engine.

The right rudder cable attachment to the rudder horn was found to have pulled out of the Nicopress copper sleeve/swage thereby disconnecting the right rudder cable from the rudder. A similar disconnect was found with the left rudder cable at the pilot-in-command's left pedal. It was determined that the correct copper sleeves were used on the correct one eighth inch diameter rudder cables but that the swaging had been carried out with the Nicropress jaws that were appropriate for a five thirty second inch cable. Four Nicopress copper sleeves were under swaged. Specialist examination subsequently concluded that the improperly constructed rudder cables probably failed at impact and not in flight.

The reason why the two pilots failed to recover the aircraft from an aerobatic manoeuvre could not be determined.

Significant Factor

The following factor was considered relevant to the development of the accident:

1. The aircraft was engaged in low level aerobatics and struck the ground for undetermined reasons.

The pilot indicated prior to departure that his intention was to track from Launceston directly across Bass Strait to Tyabb, rather than via the Bass Strait Islands. The aircraft departed Launceston with an air traffic control clearance appropriate to that intention.

After being airborne for about one and a half hours, the aircraft approached over Cape Barren Island, although the pilot had not indicated that he was diverting from the planned track. Two very low circuits were flown in the vicinity of the airstrip and while still flying low, the pilot asked the front seat passenger to tell him what he could see below the aircraft.

The survivor, who was sitting in the right rear seat, gained the impression that the pilot could not see and that he was unwell, although apparently not in pain. He did not respond when she spoke to him. She undid her seat belt, leant over the pilot and asked if the passengers could do anything to assist. The pilot did not reply and his eyes appeared glazed. She shook him, but almost immediately the aircraft descended steeply to the ground.

From the damage sustained by the aircraft and the lack of any significant ground slide, it was assessed that the aircraft had stalled from probably no higher than 150 feet and had impacted the ground in a steep nose down and left wing low attitude. Both wing flaps were found to be extended, suggesting that the aircraft was in a landing configuration.

Medical tests and examination were unable to substantiate any cardiac or cerebral event which might have accounted for the pilot's incapacitation. There are indications, however, which suggest that the incapacitation was as a result of an insulin related condition. The pilot had successfully passed his last Civil Aviation medical examination in December 1991.

Significant Factors

The following factor was considered relevant to the development of the accident:

1. The pilot apparently suffered a subtle form of incapacitation which progressively reduced his ability to control the aircraft.