OE-LAV, a Boeing B767 aircraft (flight number LDA2) enroute from Melbourne to Singapore at Flight Level 350 (FL350) suffered a reduction of oil pressure in one engine. The problem could not be rectified in flight and the engine was shut down.

The crew notified Perth ATC of the problem, advising that they were commencing an emergency descent to FL240 and required a diversion to Darwin. They were advised of opposite direction traffic, HS-TMB, a DC10 aircraft (flight number THA991), at FL330 which should be passing their present position at that time.

They were initially cleared to FL340, but the crew advised that their TCAS equipment had shown they had passed THA991 and were now diverting right of track and requiring an immediate descent to FL240.

THA 991 was instructed to descend to FL290, but as ATC could not provide a positive separation standard between the two aircraft instructed LDA2 to maintain its own separation while descending to FL240 and track direct to Darwin.

During a stock mustering operation, the head stockman, who was a passenger in the helicopter, asked the pilot to land so that he could give instructions to stockmen on the ground. The pilot landed the helicopter and commenced to secure the controls.

The stockman left his seat, stood up on the right step attached to the skid gear, and began to signal the stockmen by waving his right arm. The stockman's arm contacted the main rotor disc causing two fingers to be severed. After first aid, the stockman was transported in the helicopter to the Cloncurry Hospital where it was discovered that he had also broken his right wrist and arm.

The helicopter was slightly damaged with a broken right centre Perspex panel which was struck by the stockman's arm as it was flung from the rotor disc.

The stockman was a very experienced helicopter passenger. He had not been specifically briefed on helicopter safety aspects for this particular flight. The pilot was concerned with securing the helicopter after landing and did not see the event. He first noticed something was wrong when he saw the stockman writhing on the ground.

The pilot had been goat spotting and decided to land and wait for the accompanying helicopter to refuel.

The passenger was not feeling well, and the pilot had landed on the strip two years previously. At that time a road, that crossed the strip mid-way along it, was level with the strip surface and did not create any problems. Consequently, the pilot only conducted a cursory inspection, of the strip, prior to landing, and did not notice that the surface conditions had changed.

As the aircraft decelerated through about 15 knots, during the landing roll, it crossed the road. The depth of the road surface, below the strip surface, caused the aircraft to bounce and as it touched down again the nosewheel collided with the ridge on the far side of the road and collapsed.

Recent heavy rain and grading by the local council had changed the profile of the road, dropping its surface well below that of the strip.

The left side cabin door opened in flight, shortly after take-off. The pilot reduced power and attempted to close the door. When he found he was unable to close the door against the aerodynamic forces, he transmitted a "MAYDAY" call, advising of his intention to force land the aircraft. The aircraft was landed in a paddock with a soft surface, resulting in the nose landing gear being torn off.

A post flight inspection found no defects with the door latches. It is likely that the pilot failed to latch the cabin door properly before flight.

The aircraft was making an approach to a gravel surfaced strip in CAVOK, light wind conditions with no turbulence. The pilot reported that full flaps were extended, and a final approach speed of 75 knots was maintained until touchdown, which was slightly short of the strip threshold.

The right main wheel struck soft ground, dislodging the right main landing gear. As the aircraft continued onto the strip the remaining landing gears were also dislodged, resulting in major damage to the aircraft. All four occupants were able to exit the aircraft safely.

Just after liftoff, the pilot noticed a vibration throughout the aircraft then heard a bang and number one engine over-speed. The engine was immediately shut down and the pilot then saw that the number one propeller was missing. He made a MAYDAY call and landed immediately on the crossing runway. Inspection of the failed propeller revealed the barrel assembly, which retains the blades, had failed due to cracking, liberating both blades. During the investigation, the remaining propellers were removed and inspected but no abnormalities were observed. After repairs were completed, the aircraft was released for service. However, after 17 hours of operation, the number three propeller was removed due to an oil leak.

Inspection of the removed propeller revealed cracking in the barrel in the same area as that found on the original failure. The remaining propellers were removed, and fretting was observed on all propeller cone surfaces indicating the propellers had been operating in a loose condition.

Analysis

The manufacturers maintenance data for the propeller requires that, after installation, the propeller nut torque should be checked again after the first flight and then at 150 hourly intervals. Additionally, the barrel should be inspected for cracking every 25 hours. Review of the aircraft history revealed that the propellers had originally been fitted in the United Kingdom and the nuts were re-torqued after the first test flight. The aircraft was subsequently flown to Australia where it operated for 176 hours prior to the failure.

There is no evidence in the aircraft maintenance records that propeller nut re-torque was performed at 150 hours subsequent to its installation, or that the barrel was inspected for cracking at 25 hourly intervals. The manufacturers installation data for the propeller requires that the propeller nut be torqued to 600 lbs/ft and, whilst maintaining that torque, the wrench is given two taps with a soft mallet in the direction of nut rotation to ensure the cones are seated. Maintenance personnel involved with the propeller installation advised they had not used this method but simply torqued the nut to the required value with a torque wrench. Experiments were carried out on applying torque to a propeller nut.

It was found that when the required torque was obtained and the wrench was tapped twice with a soft mallet, the nut rotated a further 1/4 to 1/2 turn. This indicated that the nut was not sufficiently tight to seat the cones when only the initial torque was applied.

The propeller manufacturers Technical News Sheet number 26, dated January 1963, states that investigations of bracket type propellers which have suffered failure of major components have directly attributed the failures to operation of the propeller in a loose condition due to:

1. Incorrect installation.

2. Failure to check tighten or to effectively check tighten due to incorrect procedures.

Findings

1. The initial failure of the number one propeller was consistent with operation of the propeller in a loose condition because propeller nut re-torque was not carried at the recommended time periods.

2. The failure may have been averted had inspections of the barrel at the recommended intervals detected cracking.

3. The cracking of the number three propeller barrel and fretting of the other propeller cones was consistent with operation of the propeller in a loose condition as a result of incorrect nut torquing procedure.

Significant Factors

Maintenance personnel involved in the maintenance of the propellers failed to observe the requirements of the manufacturer's maintenance data.

Safety Action

The safety deficiencies identified during this investigation were corrected as they were identified. Consequently, no safety recommendations have been raised.

On approach into Melbourne the landing gear was selected to the down position for landing. The usual thump of the nose gear uplock unlatching and subsequent air noise was not evident. The nose landing gear had not unlocked and only two green indicator lights illuminated for the main gears. The aircraft was vectored away from the circuit where a manual gear extension procedure succeeded in lowering the nose gear.

The aircraft returned for a normal landing.

Investigation disclosed that a bush on the nose landing gear drag brace had seized. The aircraft's normal landing gear extension system was unable to overcome the drag created by the seized bush. It is suspected that inadequate lubrication or excessive washing out of the lubricant was responsible for the bush seizing.

A fleet check was carried out, however, all other bushes were found to be satisfactory.

During an aerial agricultural flight, the engine began to lose power. The pilot observed a low oil pressure indication before the engine suddenly seized. During the subsequent forced landing, the pilot attempted to extend the glide in order to avoid trees. However, the aircraft stalled at a height of about 30ft and landed heavily on the left main landing gear, which then collapsed

An inspection revealed that two top cylinders of the radial engine had failed, and there was no significant oil left in the engine. The engine had accumulated only 10 minutes flight time since major maintenance had been carried out, during which a top cylinder had been changed. It was later found that the oil sump plug was loose. It was apparent that the engine oil had leaked from the engine, which had then seized. The LAME who performed the engine repair was apparently distracted by other events and had failed to tighten the sump plug.

The pilot had flown the helicopter from Darwin to Jabiru, carried out some local flying at Jabiru and then returned to Darwin on the day of the accident. As the helicopter was approaching Darwin the pilot was instructed by an air traffic controller to hold position in the Palmerston area and await further clearance. Shortly afterwards the engine stopped, and the pilot was forced to complete an autorotational landing. The pilot misjudged the approach, and the aircraft landed heavily.

The pilot did not complete a flight plan prior to the flight and no evidence was found to indicate she used any form of formal fuel management to ensure that fuel available met the required reserves.

The aircrafts total fuel capacity of 200 L provided for an endurance of approximately 2.6 hours at a normal fuel consumption rate of 75 L/hour. The flight to Jabiru took 2.5 hours. A total of 194 L of fuel was required to fill the tanks following this flight. The tanks were also refilled following the local flying. Although almost all the fuel had been exhausted on the flight to Jabiru the pilot departed for the 2.5 hour flight to Darwin without having made any alternative fuel arrangements. The fact that the aircraft had almost run out of fuel on the flight to Jabiru did not register.

When the pilot was instructed to hold position in the Palmerston area and await a further clearance she advised the controller that the aircraft was low on fuel but she did not communicate any urgency about the situation. Ten minutes later, whilst still in a holding pattern, the engine stopped as a result of fuel exhaustion. The helicopter had been airborne for 2.6 hours when the engine stopped.

The pilots actions indicate she was never sufficiently aware of the aircraft's fuel situation. The lack of planning and the failure to use a formal management procedure probably exacerbated the situation.

The pilot initiated normal gear selection after arriving in the circuit area at Manilya. The gear extension process stopped after the nosewheel and right main gear had extended. The pilot checked the circuit breakers and recycled the gear twice more with the same result.

The pilot decided to return to Carnarvon where the gear could be inspected visually. Observations by a pilot and engineer confirmed that the left main gear was up. Use of the manual extension system and the introduction of 'g' forces were unsuccessful in causing the left main gear to extend.

After discussion with engineers in Carnarvon and Perth the pilot elected to carry out a wheels up landing on the grass flight strip beside sealed runway 18. The landing was successful.

An inspection of the landing gear systems disclosed that the hinge bolt, from the front hinge of the left landing gear door, was missing. The missing bolt allowed the landing gear door to twist, in the airflow, jamming the door closed and preventing the left gear from extending.

The missing bolt was not recovered. A number of landing gear hinge bolt nuts, including one that was adjacent to the hole left by the missing bolt, were recovered from the channel surrounding the landing gear bays on both sides of the aircraft. It was not possible to determine if any of the nuts came from the missing bolt. There was no evidence of stress, in the area of the missing hinge bolt, to indicate that the bolt had been working prior to its loss.

The landing gear doors had been removed, inspected for cracking, and replaced eight flying hours prior to the accident. The gear had been extended and retracted a number of times, without apparent problems, after the replacement and prior to the final flight. The failure sequence indicates that the bolt was probably in place for a period following the maintenance and fell out on the accident flight. No history of problems with the hinge bolts was disclosed during the investigation.

It was not possible to determine whether the bolt failed and fell out, as a result of fatigue or overload, or if it was incorrectly fitted following the maintenance conducted shortly before the accident flight. There was some evidence that the engineer responsible for re-fitting the suspect bolt was distracted by a personal problem during that process however he did not recall any specific event that may have contributed to the loss of the bolt.