FACTUAL INFORMATION

The helicopter had undergone a maintenance check which included changing both forward and aft coupling assemblies of the main driveshaft and the forward boot assembly. Prior to release for service, vibration monitoring tests were carried out on the ground and during flight. On the final flight, whilst climbing to 4,000 ft in preparation for a descent test, the maintenance crew observed an increase in longitudinal vibration of the main driveshaft. On reaching 4,000 ft, there was a noticeable grinding noise and all power to the main rotor was lost. Following the driveshaft failure, the pilot carried out an autorotation into the only available open field. The field initially appeared flat but as the helicopter approached the ground level, the pilot saw that it was undulating and sloped upwards in the direction of his approach. The pilot was unable to correct for this in time to avoid a heavy landing.

A coupling is fitted to each end of the driveshaft. Each coupling is a splined unit packed with grease as a lubricant between its inner and outer components. A rubber boot assembly bolts to the outer coupling to contain the grease as the assembly rotates. An O-ring packing is retained in a groove in the boot as a seal between the boot and the outer coupling.

Investigation found that the main driveshaft forward coupling assembly had failed. The outer coupling remained intact, but the splines of the inner coupling had failed. A metallurgical examination determined that, though the coupling had probably met manufacturing specification, it had been subjected to high temperature which resulted in weakening of the core material underlying the nitrided zone. The splines were then unable to transmit the applied torque to the outer coupling and failed from overload. The associated rubber boot assembly had disintegrated, its attaching bolts were loose, and the locking wires were broken. There was some charred debris in the O-ring groove of the boot, which was probably the remains of the O-ring which formed the seal between the boot and the coupling. The grease lubricant, normally retained in the coupling by the boot assembly, had been ejected and was spattered over the driveshaft well.

The forward boot assembly had been requisitioned from stock under the existing part number. However, the boot had been modified by the manufacturer, given a new part number, and issued as a replacement part. The modification included securing the grease dam in the boot assembly by a process known as roll staking. This process consisted of mechanically removing material from the O-ring groove wall and rolling it to lock the dam in position. The operation modified the O-ring groove profile so that steps were formed in the inner circumference of the groove. There was no information provided by the manufacturer to advise maintenance personnel of the modification.

ANALYSIS

The failure of the driveshaft coupling was consistent with a failure of the O-ring. This provided an open path for the grease to be ejected by centrifugal action as the driveshaft rotated at its operating speed of 6,000 RPM. Failure of the O-ring would immediately reduce the torque on the attachment bolts. It is likely that the ensuing vibration resulted in failure of the locking wire. The loss of the grease resulted in overheating of the coupling gears which eventually failed and all power to the main rotor was lost.

Maintenance personnel, unaware of the modification to the O-ring groove, probably allowed the O-ring to be pinched between the boot and the coupling during assembly. Bolt torque would have appeared normal but during operation the O-ring would fret between the mating surfaces until it failed, leaving a path for the grease to escape.

SIGNIFICANT FACTORS

1. The manufacturer did not provide adequate details of the modification to maintenance personnel.
2. Maintenance personnel, unaware of the modification to the boot, probably allowed the O-ring to be pinched when the boot was mated to the coupling during assembly.

SAFETY ACTION

The Bureau of Air Safety Investigation made the following recommendations to the Civil Aviation Safety Authority and to Bell Helicopter Textron Inc on 23 January 1997:

"R960155

"The Bureau of Air Safety Investigation recommends the Civil Aviation Safety Authority advise all Bell Helicopter

412 operators in Australia of the potential, during installation, for the O-ring (PN 204-040-691-003) to sag in the

O-ring groove of the (PN 212-040--688-003) coupling and hence, become pinched between it and the (PN 212-040-176-101) boot assembly. This would allow a path for the grease lubricant to escape due to the centrifugal forces acting on the driveshaft during its normal operation, thereby causing the coupling to overheat and fail." "R960156

"The Bureau of Air Safety Investigation recommends that Bell Helicopter Textron Inc. include a cautionary note in the relevant section of the Bell 412 maintenance manual (BHT-412-CR&O, at 63-9 ASSEMBLY-MAIN DRIVE

SHAFT), warning of the possibility for the O-ring to sag during installation in the replacement PN

212-040-176-101 boot assemblies and hence, allow the potential for pinching to occur between the boot and coupling assemblies. This would allow a path for the grease lubricant to escape due to the centrifugal forces acting on the driveshaft during its normal operation, thereby causing the coupling to overheat and fail."

1.3 The rejected take-off was accomplished at a speed reported by the captain to be approaching V one (V1), however the Flight Data Recorder information could not be retrieved, and the actual speed is unknown. V1 is the maximum speed from which the aircraft can be safely stopped when take-off is discontinued. The aircraft was stopped at taxiway Bravo 4 (B4) which is approximately 2200 metres from the threshold of runway 15.

1.4 Examination of procedures in the Qantas Airport Services Manual revealed that there was no standard procedure for loading and unloading a container compartment. The manual states that many variations of loading and unloading can be accomplished with proper selection of control switches and restraint hardware. The design of the sill locks is such that although they are painted red, there is no visual indicator to warn that they are not locked down before the compartment door is closed. There is no reason to believe that had the loader not been interrupted in his task that he would not have put the sill locks down. The leading hand who asked the loader to man the tug for pushback, omitted to check that the locks were engaged before he closed the door. He stated that this was due to a variance of procedure, because he deploys the locks before lowering the bridge, and the loader deploys the locks after lowering the bridge. The interruption to the procedure, at the point where the locks would have otherwise been engaged was thus unfortunate and led to the omission.

1.5 The sill locks provide vertical and lateral restraint on one side of the container only. The container was restrained vertically and longitudinally by the remainder of the locking devices and could not have moved if the aircraft had become airborne.

3. CONCLUSIONS

Findings

1. A container in the rear cargo hold at position R44 was not fully restrained by the aircraft locking system.
2. The persons responsible were aware of their responsibility, but due to task interruption, and variance in procedures, a final check to ensure the sill locks were activated was omitted.
3. There was no warning device or mechanical means to prevent the door from being closed when the sill locks were not activated.
4. There was no specific procedure laid down for loading or unloading, however the Load Instruction Report certifies that the aircraft has been loaded in accordance with the Aircraft Load and Balance Manual, and that the load is secured by the aircraft locking system.

Significant factors

1. The aircraft departure was late.
2. The loading team changed positions to save time.
3. Loading procedures were not standardised.

During a ferry flight the aircraft's engine began to run rough, then stopped about 20 seconds later.

The pilot made a successful forced landing into scrub-covered terrain in an inaccessible area of a national park, with the aircraft suffering only minor damage.

An examination of the engine revealed the cam ring had fractured.

The pilot reported that, during the landing roll, as the aircraft slowed through about 40 knots, three cows ran on to the runway. The right propeller of the aircraft struck one of the cows and the pilot was unable to prevent the aircraft running off the end of the strip into a fence.

The pilot indicated that the runway was clear when he checked it on downwind, base, and finals. The strip was surrounded by an electric fence, but the fence was not activated at the time the aircraft landed.

During cruise the aircraft suffered an engine failure with oil covering the windscreen. The pilot carried out a successful landing onto a beach 40 km west of Milingimbi.

Later as the tide filled the aircraft, which was undamaged, became immersed in salt water.

An inspection of the engine indicated that the number six cylinder gudgeon pin had failed allowing the connecting rod to separate from the piston. As the engine continued to rotate the loose connecting rod struck and holed the crankcase.

"As a result of these reports, the Authority requested Airservices to issue a NOTAM on 27 October 1995 to correct the position of the chart symbol depicting this operation, which is incorrect on the Brisbane VTC but correct on the Oakey VTC (both dated 7 December 1995).

"In discussion with the operator it appears that, despite his making the required broadcasts prior to parachutists exiting the drop aeroplane other traffic in the area are not responding to those broadcasts and therefore parachutists are not aware of traffic which will pass below them whilst they are still under canopy some five minutes later. This traffic may be up to 15 miles from the drop zone at the time the drop aircraft broadcasts its advisory message and may not recognise the potential for confliction.

"A further difficulty is that the drop zone is only four miles from the frequency change point which coincides with the Amberley CTR boundary, and so broadcasts are often made on both frequencies. As an additional precaution, the target control officer on the drop zone monitors traffic on a portable VHF transceiver.

"The operator has previously sought the advice of the Queensland RAPAC on the establishment of a formal danger area to provide an enhanced warning to itinerant aircraft of the extent of the hazard posed by their overflying this area. However, the Authority is not convinced that a danger area is necessary in this case.

"Nevertheless, since airspace is now the responsibility of Airservices Australia, your report and recommendation have been passed to them for consideration.

"The questions of re-issuing a safety poster about parachuting activity and publishing an article on ways to minimise risks when flying near a parachute drop zone, have been raised with the Authority's Safety Promotion Section and some further educational material is under consideration."

The following response was received from Airservices Australia on 6 May 1996.

"Subject: BASI IR950225 Gatton

"Reference incorrect location of parachute symbol;

A NOTAM was issued alerting pilots to the parachute symbol location. The symbol appears on the 20 June 1996 charts at the amended position.

"The proposal for a Danger area was referred to the Queensland Regional Air Co-ordinating Sub Committee (RACS) for consideration.

"As part of the "Process 5 for the Origination, Co-ordination, Ratification, Promulgation and Registration of Airspace and Air route Amendment Proposals " the recommendation was considered by the Queensland Regional Airspace Users Advisory Council (RAPAC).

"The RAPAC did not support the establishment of a Danger area. Further action regarding chart symbols, pilot education and consultation with CASA is to be undertaken by the RACS."

The Bureau of Air Safety Investigation has classified these responses as: CLOSED - PARTIALLY ACCEPTED.

The pilot completed an airfield inspection prior to joining the circuit for landing. He noted from the movement of the trees that there was a crosswind from the right on runway 30 but he was unable to find the windsock to determine its strength. The pilot flew a normal crosswind approach, with the aircraft yawed into wind, selecting full flap (300) at a speed of 70 kts on short finals. He applied left rudder and right aileron, during the landing, to counter the crosswind. The aircraft bounced on touchdown and began to drift to the left. The application of full right aileron failed to stop the drift, and the pilot applied full power in an attempt to go-around. By this time the aircraft had left the runway and was heading towards a gravel mound. The aircraft appeared reluctant to get airborne and the pilot retracted the flaps to 200 in an attempt to improve performance. The aircraft collided with the gravel mound before it became airborne.

A video of the landing and accident indicated that a strong wind was blowing and that there were significant gusts. The aircraft was affected by one such gust as it touched down the first time and it was evident that the pilot was unable to counter its effect. There was insufficient room following the application of power for the aircraft to become airborne before it collided with the mound. The windsock had been shredded by strong winds and was unusable as an indication of wind strength. The pilot had completed crosswind refresher training on the weekend before the accident flight and had assessed the conditions as difficult but safe.

The pilot was taxiing the aircraft for take-off at the time of the accident. He had been manoeuvring the aircraft from one side of the taxiway to the other in an attempt to maintain adequate forward visibility. The pilot was wearing his goggles, because of a cold wind, and the sun was in a position that reduced visibility significantly. He observed another aircraft immediately ahead and despite closing the throttle and applying the brakes the two aircraft collided. The other aircraft was stationary on the taxiway whilst the pilot completed the pre-take-off check list.

Visibility from the Tiger Moth's rear cockpit during taxy is less than optimum at the best of times. It is probable that the sun glare momentarily distracted the pilot, and he did not see the stationary aircraft until it was too late to avoid it.

The pilot reported that the wind on the day of the occurrence, was very strong, approximately 30-40 kts at 120-130 degrees. The runway alignment was 120 degrees. As a consequence of the limited available runway length, the pilot elected to carry out a short field approach and landing. On short final to land the aircraft encountered strong windshear, which resulted in a heavy landing.

After touchdown, the left main landing gear support strut collapsed due to excessive side loads and the gear folded rearward, causing damage to the underside of the wing and flap.

All persons on board were able to exit the aircraft safely.

Aircraft was being vectored for a visual approach at Cairns, with an assigned radar lowest safe altitude of 3600ft. Approximately 18km north-west of Cairns, while heading east towards the coast, the ground proximity warning alarm activated. An immediate climb to 4000ft was initiated. The aircraft did not descend again until after crossing the coast to become visual and then made a visual approach and landing. No breakdown of separation occurred.

Later engineering examination confirmed that the alarm activation was a false indication, which was caused by an electrical fault in the GNS Omega navigation system.