The pilot was flying the helicopter in a spraying operation over a paddock adjacent to a farmhouse. A study of his map and an aerial inspection had led him to believe that a major spur powerline terminated at a transformer near the farmhouse. However, this was not the case as the three-phase powerline continued on in long spans.

He had almost finished the task and required one final spray run at 90 degrees to his previous swaths and the unseen powerline bordering the paddock. As he pulled up after the run, the spray boom collected the wires. The helicopter gyrated, losing the tail boom to a main rotor strike, and crashed some 15 metres beyond the powerline.

The pilot had not seen the powerline at any stage.

Factual information

The aircraft was on an approach to Perth Airport. At 400 ft and 80 kts it began to vibrate severely. The vibration appeared instantly at full amplitude and did not vary for the remainder of the flight. The pilot declared an emergency and carried out a precautionary landing in a transport parking area. The aircraft was not damaged during the landing. The stainless-steel leading-edge strip of one tail rotor blade was missing. The out-of-balance tail rotor caused substantial damage to the tail boom in the vicinity of the tail rotor blade.

The stainless-steel leading-edge strip detached because the bond between the strip and the blade body was inadequate. There had been little transfer of adhesive to the steel and the adhesive contained many voids. The leading-edge strip that remained attached to the other blade and its adhesive exhibited similar characteristics to the failed strip. The lack of bonding had allowed moisture into the area between the steel strip and the blade, causing further deterioration.

Analysis

A review of BASI air safety occurrences and the Civil Aviation Authority defect reporting database did not disclose any other reported instances where the leading-edge strips had become detached during the life of the blade. The blade was manufactured in early 1991. The manufacturer reported that the pre-1991 manufacturing process had produced a number of faulty blades, and the process was changed. It could not be determined if the blade had been manufactured using the pre- or post-1991 process. The factors leading to lack of bonding during the manufacture of the failed blade could not be determined.

Because debonding was seen as a significant potential problem, the operator required pilots to carry out a coin-tap test on the blade on a daily basis to determine whether debonding had occurred. A check was conducted by two different pilots on the day of the accident without disclosing any sign of debonding in the leading-edge strip. In addition, the blades had been inspected on many previous occasions by both pilots and qualified aircraft engineers. These inspections also failed to disclose the lack of bonding. The lack of bonding on the tail rotor blades extended over the whole leading edge strip area on both blades. Consequently, it is unlikely that the coin tap-test would have produced sufficient variation in the sound between different parts of the blade for an observer to recognise debonding.

Significant Factors

The following factors were determined as being significant to the accident.

1. The bonding process used to attach the leading-edge strip to the tail rotor blade was inadequate in that an unacceptable number of voids were left after the process was complete.
2. The use of a coin-tap test as a check for delamination was inadequate in that it may not have disclosed that the strip had delaminated to the point that failure was imminent.

Safety Action

1. The manufacturer has introduced a different bonding process to ensure a lower likelihood of debonding.

The helicopter was cruising at 200 feet above ground level whilst the pilot searched for a vehicle that he wished to rendezvous with. Having sighted the vehicle coming towards him from the right front quarter, the pilot decided that rather than conducting a fly-past to attract the driver's attention he could achieve the same result by landing the aircraft beside the road and in front of the vehicle. To achieve this the pilot placed the helicopter in a hard right turn and entered a steep descent. As the helicopter rolled out of the turn the pilot realised that he had insufficient height available to completely arrest the descent before impact. Although the pilot's attempt to cushion the landing was partly successful, the aircraft touched down heavily and somersaulted.

During the landing roll, at about 25 knots, a wind gust from the left caused the left wing to rise and the right wingtip contacted the ground. The propeller contacted the ground, and the aircraft nosed over and came to rest inverted.

The pilot said that he did not observe any sign of crosswind during the approach.

The flight was uneventful until arrival in the circuit at Scone where the pilot reported he had difficulty in determining the position of the windsock and wind direction. He did not commence descent until the landing direction was ascertained and then elected to join the circuit for runway 11. After manoeuvring for crosswind, and making the required radio transmissions, the pilot realised he was too high and too close to the runway. He elected to adjust the circuit and leave the lowering of the landing gear until the base leg. On base leg, the aircraft was still too high, so the engine power was reduced to idle. The aircraft touched down a considerable distance along the runway with the landing gear retracted.

No defects were found with the landing gear actuating or warning systems subsequent to the accident. The pilot and front passenger were wearing headsets during the flight and stated they had not heard the landing gear warning horn until just prior to touchdown. The rear seat passenger heard the horn but did not notify the handling pilot.

VH-TGT was conducting solo circuit training using right hand circuits for runway 21R, and at the same time VH-XYI was conducting dual circuit training using left hand circuits for runway 21L.

On downwind VH-XYI was cleared by the air traffic controller responsible for runway 21L operations to land ahead of another aircraft inbound from the north east. To increase separation the instructor decided to make a close in, steep gliding approach.

VH-TGT was cleared for a touch and go landing on runway 21R by the air traffic controller responsible for runway 21R operations, then both controllers became involved in monitoring other aircraft in their respective areas of responsibility.

An observer in the control tower noticed VH-TGT was on short final approach for runway 21L with VH-XYI, also on final approach, and descending rapidly towards VH-TGT. VH-XYI was instructed to go around, the pilot taking further avoiding action by banking to the left.

The student pilot in command of VH-TGT had less than 2 hours solo experience.

The pilot reported that shortly after take-off, at approximately fifteen feet above ground level, the aircraft yawed to the right and collided with some low scrub. The aircraft came to a stop clear of the right hand side of the strip. It was also reported that the strip met all requirements and that there were no apparent control malfunctions.

The reason for the loss of control was not determined.

The aircraft was descending in icing conditions with the engine anti-icing system selected ON. A loud bang was heard from the right engine and the aircraft yawed to the right with an associated reduction in torque. The right ignition light illuminated followed by right engine re-light with subsequent normal engine operation. The descent continued for an uneventful landing.

Investigation found one compressor blade bent. The blade was dressed in accordance with approved procedures. A subsequent ground test determined the engine anti-icing system was serviceable. It is likely that ice ingestion resulted in a short-term power 'rollback' coupled with minor compressor blade damage. Power was restored by the normal functioning of the auto-ignition system.

The pilot reported he was practising crosswind landings on runway 08. The wind was estimated as 135/15 occasionally gusting to 180/30. The approach was normal but as the aircraft was flared for touchdown, at a height of about five feet, a sudden gust lifted the right wing. The left mainwheel contacted the ground heavily and the left main landing gear collapsed. The aircraft yawed violently to the left, collapsing the right main gear before the aircraft came to a halt.

The pilot reported that the aircraft was being landed with about a 10 kt crosswind from the left. After the landing gear was selected down, the pilot viewed the three green landing gear down and locked lights. The approach was normal with the crosswind being countered by flying left wing down. The left wheel contacted the ground first, but the right main gear leg collapsed as it contacted the ground. The pilot lost directional control of the aircraft which slid to a halt about halfway along the strip near the left side.

Later inspection revealed that the lower forward lug on the bell crank assembly had failed resulting in the over-centre lock not being fully extended and the gear leg to collapse under the weight of the aircraft. The reason for the lug failure was not determined.