1. FACTUAL INFORMATION

Sequence of events

The aircraft was involved in Civil Search and Rescue Unit training at the time of the occurrence and the trainee drop master was undertaking his first live dispatch of a twin raft training pack under the supervision of an instructor. The aircraft was being flown at 120 knots and 200 feet above sea level for the exercise.

The drop proceeded normally until the first raft pack was dispatched after which the trainee retained his grip on the second raft pack beyond the point in time when the second pack should have been dispatched. As the rope reached full length a tug was felt and shortly afterwards the first raft pack entered the water placing a much greater load on the rope causing the second raft pack to be pulled from the trainee's grip.  It struck the rear door frame before exiting the aircraft, causing substantial damage.

Raft dropping procedures

Raft packs connected by 440 m of rope are normally dispatched from the aircraft at six second intervals allowing the rope to be pulled completely from special containers attached to each raft pack. The raft packs are normally located one on top of each other and protrude through the door. They are pushed outwards and downwards by the dispatcher to ensure they remain clear of the aircraft. The drop master may also use an alternative procedure by waiting until he feels a tug on the rope before dispatching the second raft. During training, raft packs made from a solid wooden cylinder and webbing are used in lieu of rubber rafts. The training pack has less elasticity than the actual pack.

When an actual raft is dropped it begins to inflate during its descent and will not generally contact the water before the second raft is released. However, a training raft pack does not inflate and therefore it falls at a faster rate, entering the water sooner than an actual raft. On this flight the early entry into the water of the training pack led to the uncontrolled release of the second raft and the subsequent damage to the aircraft. The twin raft deployment system does not include a weak/frangible link to protect the aircraft from damage resulting from such circumstances.

Pre-flight training/briefing

The trainee drop master had been trained and subsequently briefed for a single raft drop. On the day of the occurrence the aircraft to be used for the single raft training became unserviceable and the exercise was re-scheduled for a twin raft drop. He had not been trained or briefed for the twin drop until immediately prior to departure. Before each flight the crew normally received a briefing from the pilot-in-command on the procedures and calls to be used during the drop.

During the preflight briefing by the pilot-in-command, it became evident that the trainee drop master was not familiar with the twin raft drop procedures. The briefing was discontinued to allow the trainee drop master to be given instruction on twin raft drops by the drop master instructor. The preflight briefing was subsequently resumed but the drop master instructor did not attend this briefing as he had become occupied with other duties. The trainee did not carry out any dummy runs to practise the twin raft drop procedures.

During the flight the drop master instructor introduced procedures that had not been explained during the preflight briefing. In addition, the intercom between the drop master and pilot failed and hand signals (a normal alternative procedure) were used.  Additionally, the clock, used for timing the drop sequence, was stopped during the live drop run causing the drop master to lose his timing reference.

3. CONCLUSIONS

Findings

1. The trainee drop master was inadequately prepared for the twin raft sequence due to insufficient instruction and a lack of dummy training runs.
2. There was a breakdown in standardisation and communication because the drop master instructor did not attend the preflight briefing given by the pilot-in-command.
3. The twin raft deployment system does not include a weak/frangible link to protect the aircraft from damage should there be a hang-up and one raft pack enters the water.

Significant Factors

1. The training system in use was not mature enough to cope with a last-minute change in the program caused by an aircraft unserviceability.
2. Training staff did not ensure that drop master training was adequate and that procedures were clearly understood prior to departure for the flight.
3. The design of the training raft packs was deficient in that it did not provide a failsafe system in the event of a hang-up during normal dispatch.

4. SAFETY ACTION

4.1 The Civil Aviation Authority suspended all training using the twin raft system pending the results of an investigation into the safety of the system.

4.2 The Bureau of Air Safety Investigation issued Safety Advisory Notice SAN 940076 on 29 March 1994, suggesting that the Civil Aviation Authority review the Search and Rescue twin life raft system to ensure:

1. that a weak/frangible link is included between the two rafts for twin unit deployments;
2. that ab-initio trainee drop masters undertake at least one practice drop run before attempting an actual deployment; and
3. that communication and teamwork between flight crew and the drop crew is improved on SAR training flights.

The Civil Aviation Authority responded on 7 June 1994 advising that:

1. in future there will be no change of the supply drop process during a planned training program for an ab-initio drop master trainee;
2. ab-initio trainee drop masters will undertake a minimum of ground training drop simulation and one airborne practice drop prior to an actual life raft/dummy unit deployment;
3. the Drop master and Pilot SAR Manuals will be amended to delete the use of the tug on the rope as an alternate indication to an elapsed time of 6 seconds for the release the second raft;
4. the drop master instructor and the pilot tutor will attend the preflight briefing given by the pilot in command, prior to each training flight and all crew members will attend the preflight brief given to the trainee drop master;
5. where possible training is to be conducted with rubber compound units, - Technical Services Division (TSD) are about to place an order for the manufacture and supply of rubber compound units, which will replace the wooden logs currently in use. A time frame for delivery and replacement is not known; and
6. TSD have developed a weak link for use on all training equipment (Single, Twin and Multi-unit drops). Testing of this weak link is presently being conducted.

Status of response: Closed - accepted.

The pilot reported that while flying at 350 feet above ground level, maintaining 50 knots, the engine started to vibrate violently and lose power until it stopped. Prior to the power loss, all temperatures and pressures were normal. The pilot entered autorotation but due to the unsuitable terrain he had to make a very steep descent to put the aircraft onto a suitable landing site. In doing this, he made a heavy touchdown which resulted in a main rotor blade striking the tail boom causing substantial damage.

The engine failure was later determined to have been caused by failure of the number two connecting rod assembly. The failure of the assembly was caused by fatigue crack growth in the connecting rod cap. The factors that contributed to the fatigue crack initiation were not determined.

ASOR Summary

The aircraft was to depart via a Wollongong One Standard Instrument Departure (SID) after taking off from runway 16. After this instruction had been passed to the aircraft, the duty runway was changed to runway 07. This information was passed to the aircraft along with the instruction that the Wollongong One SID was to be flown. (The Wollongong One SID from runway 16 is different to the Wollongong One SID from runway 07.) In the event, the aircraft was observed on radar after take-off from runway 07 to commence to fly the Wollongong One SID applicable to runway 16. The aircraft was then instructed to track direct to Wollongong.

Safety Action

The Bureau of Air Safety Investigation recommends that the Civil Aviation Authority:

(a) review the presentation of standard departure instructions in order to ensure that they are clearly laid out to make them easily assimilated, and

(b) review the instructions for each runway so that they are contained on individual charts or, are clearly delineated on each chart.

The helicopter was tracking coastal at about 500 feet AMSL when the pilot saw a crocodile on a riverbank and commenced a descent to enable photographs to be taken. He made a right turn to position the helicopter into wind while descending to a height of about 100 feet and decelerating to 10-20 knots.

As the helicopter came out of the turn the pilot applied normal up collective control and left anti-torque pedal to regain level flight which was immediately accompanied by a severe vibration. The helicopter began to rotate rapidly to the right and the pilot applied full left pedal, but with no response, the feel on the pedals being as if they were detached from the tail rotor system.

The pilot lowered the collective and applied forward cyclic in an attempt to control the rotation and vibration. Although the rotation rate slowed, the helicopter rotated through another 2-3 turns and descended to about 30 feet above the sea. The pilot realising that he would be unable to effect a successful recovery, landed the helicopter in the water with a forward speed of about 10-20 knots in a tail low attitude while still rotating to the right.

The helicopter rolled inverted and floated upside down for 3-4 minutes. All occupants evacuated the helicopter and swam ashore. The helicopter sank, but after a while it resurfaced then floated out to sea on the tide and was recovered the next day. The tail boom was found to have been severed behind the horizontal stabiliser, the vertical fin, tail rotor gearbox and tail rotor being lost in the sea.

Subsequent investigation revealed that the tail rotor drive forward short shaft had failed due to torsional overload. The severed tail boom, when matched to a serviceable helicopter of the same type, showed that the damage and impact marks were found to align with the tail rotor blades. The tail rotor drive long shaft had only slight impact damage and had uncoupled intact off the splines at the tail rotor gearbox, indicating that a main rotor blade impact had not caused the tail boom to fail.

The tail boom was severed by a direct strike from a tail rotor blade under power, which then caused the tail rotor drive short shaft to fail under load. It was not possible to determine the reason why the tail rotor blade struck the tail boom.

The student pilot/owner and an experienced private helicopter pilot, who was not endorsed on type and did not hold a valid medical certificate, decided to ferry the helicopter. Enroute, they elected to enter an autorotation to practise a forced landing from about 1,000 feet above the ground. When attempting a power recovery near the ground, they realised that the engine had stopped. During the autorotative touchdown the main rotor cut through the tail boom. The landing gear skid assembly broke, and the helicopter rolled onto its left side.

No mechanical failure of the airframe or engine has been found which may have contributed to the accident.

At the time of the flight the relative humidity was about 88% and the outside air temperature about 13 degrees Celsius; conditions were ideal for the formation of carburettor icing. The engine is water cooled and is fitted with a water jacket on the carburettor. If the tap adjoining the carburettor is turned on, hot water will circulate to warm the carburettor and thereby counteract carburettor icing. On the standard Rotorway EXEC 90, the tap must be turned on before flight because there is no means to turn it on from the cockpit. On VH-YCP, the tap was turned off.

Subsequent to the accident it has been noted that the carburettor air temperature gauge fitted to the console reads about 10 degrees celsius colder using the external air scoop, which is an Australian modification, as opposed to the original Rotorway design. Since the accident, the Civil Aviation Authority has amended the permits to fly. Until the matter of carburettor heat is resolved, the induction anti-icing system must be turned on for all flights in conditions of outside air temperature below 24 degrees Celsius; and flight in conditions of outside air temperature 10 degrees or below in visible moisture is not permitted.

Significant Factors

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

1. The carburettor heat water jacket was not turned on before the flight.

2. Prevailing conditions were conducive to the formation of carburettor icing.

3. The engine probably failed due to carburettor icing.

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.