The private pilot conducted a daily inspection, loaded five people and luggage on board the aircraft and attempted a take-off on runway 17 right. When the aircraft failed to rotate, the pilot rejected the take-off. He attempted a second take-off on runway 17 right, using the extra runway distance available before the displaced threshold. Again, the aircraft failed to rotate, and the take-off was rejected. He taxied back to dispersal, unloaded 75 kilograms of luggage, and attempted a third unsuccessful take-off. Next, he unloaded the four passengers and attempted a fourth take-off which was also rejected. The pilot taxied back to dispersal and acquired the services of a flying instructor in an attempt to determine why the aircraft would not rotate when he pulled the control column back.

The instructor agreed to fly a circuit with the pilot. The pilot carried out a take-off with the instructor monitoring. Because the instructor was not flying the aircraft he was not aware that the pilot had to apply stabilator back trim to rotate the aircraft. During the crosswind leg the instructor noted that the pilot was holding an unusual control column position to achieve the climb attitude. The instructor took over the controls but realised that, although the control column pressures felt normal and ailerons performed normally, there was little, or no attitude change when the column was pushed forward or pulled aft.

Using engine power variations and stabilator trim, the instructor carried out a long, shallow, landing approach for runway 17 right. The instructor was unable to reduce the rate of descent enough to prevent a hard landing. On touchdown the right main landing gear leg broke and the aircraft skidded off the runway to the left.

It was subsequently found that stabilator control was lost because the torque tube lever (drive horn) slipped on the stabilator torque tube. There was evidence of lubricant between the clamping surfaces of the drive horn and the stabilator torque tube. Lubricant had been applied to the area during recent assembly in an attempt to prevent corrosion which had occurred in the past on an unpainted torque tube. Lubricant may also find its way onto the torque tube/drive horn when the jack screw, which is located immediately above the drive horn, is lubricated.

The rigging screw/safety screw, which located the drive horn on the torque tube, had sheared progressively. It was estimated that this screw will shear with a control force of 60 pounds.

A series of tests was carried out to measure the breakaway and sliding forces of the drive horn on the torque tube with the drive horn clamp bolts properly torqued between 50- and 70-inch pounds. These tests were conducted without fitting a rigging screw. With lubricated surfaces, the maximum breakaway force was 96 pounds with the clamping bolts torqued to 70-inch pounds. The breakaway force fell to 45 pounds with clamping bolts torqued to 50-inch pounds. The highest breakaway force measured during the tests was 165 pounds with dry surfaces and 60-inch pounds torque on the clamping bolts.

These tests indicated that the current design does not comply with FAR 23.397 standards because the control system is not capable of transmitting a force of 200 pounds to the stabilator without risk of slippage of the drive horn on the torque tube.

The rigging/safety screw probably failed as a result of being subjected to repeated shearing forces during flight.

Significant Factors

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

1. The pilot(s) conducted repetitive rejected take-offs rather than seek qualified engineering advice.
2. Because of the current design of the attachment of the drive horn to the stabilator torque tube, the control system does not comply with FAR 23.397 standards in that it is not capable of transmitting a force of 200 pounds to the stabilator without the risk of slippage of the drive horn on the torque tube.
3. The friction grip surfaces between the drive horn and the torque tube had been lubricated during installation thereby making slippage of the drive horn more likely to occur.
4. It is possible that lubricant may find its way onto the torque tube/drive horn area because maintenance engineers periodically lubricate the screw jack located close to and above the drive horn.

Safety Action

In response to preliminary investigation advice, the Civil Aviation Authority issued Direct Mail Airworthiness Directive AD/P68/38 in March 1992. This directive required initial and repetitive integrity inspections of the stabilator drive horn to torque tube clamped joint.

AD/P68/38 Amdt 1 was issued 6/92 to reflect and require compliance with Partenavia Service bulletin P68-87. This amendment aligned the Australian AD with the country of origin AD FAI 92-077 requirements.

The current AD/P68/38 Amdt 2, issued 9/92, reflects and requires repetitive compliance with Partenavia SB P/68-87 rev 1 which introduces a more specific clamp bolt torque and a new safety screw of a different material.

The Bureau of Air Safety Investigation engineering evaluation and testing of the stabilator horn to torque tube clamped joint, contends that the design fails to meet the FAR 23 design standards. Further comparisons, between the BASI engineering report and tests and the Partenavia engineering tests revealed that, when the joint was lubricated it failed to transmit limit loads and raises doubts whether the new NAS1105 safety screw by itself is capable of transmitting the limit load with a factor of 1.5 as suggested by Partenavia.

The Bureau of Air Safety Investigation therefore makes the following recommendation:

R940071

1. That the Civil Aviation Authority review the Partenavia engineering   data (in comparison to the BASI engineering reports) to ascertain whether or not this friction clamped joint meets the FAR 23 design standard.
2. That the Civil Aviation Authority continue to negotiate with the manufacturer to produce a scheme for this primary control which positively attaches the Torque Tube Lever (Drive Horn) to the Stabilator Torque Tube.

While enroute from Darwin to Maningrida at 9000 feet and at 12nm NE of Nabarlek, the pilot, who was the sole occupant, noticed a drop in the starboard engine manifold pressure.

He looked at the engine and saw smoke coming out of the right hand side inspection vent. The manifold pressure had fallen to 15in Hg and by this stage, oil was starting to leak from around the starboard engine cowl at a considerable rate.

The pilot carried out the 'engine fire' procedure drill and secured the engine, advised ATC and diverted to Nabarlek for landing. The propellor continued to windmill with the pitch lever in the feathered position until the aircraft speed reduced to 90 knots IAS on final. The propellor appeared to be about 90 % feathered. The aircraft landed safely.

Engine damage was caused by failure of the crankshaft counterweight flange allowing the counterweights to separate. The crankcase was damaged resulting in a severe oil leak onto the turbocharger causing the smoke seen by the pilot.

The pilot of VH-LQA was conducting a practice ILS approach for runway 23 at Adelaide Airport. Approaching the localizer (LLZ) at 3000ft air traffic control (ATC) instructed him to enter a holding pattern between 28 and 34 km north-east of Adelaide to maintain horizontal separation standards with VH-YMJ, which had been cleared by ATC to intercept the 23 LLZ at 3000ft, from the east, for its arrival to Adelaide.

After completion of the holding pattern, and not having received any further instructions from ATC, the pilot of VH-LQA believed he could continue the practice ILS without any further clearance and intercepted the LLZ.

He was instructed three times in quick succession to turn right onto a heading of 310 degrees, and the pilot of VH-YMJ was instructed to continue turning left. The two aircraft passed at the same height with less than 5km horizontal separation.

During the take-off sequence the nose locker door, which had not been correctly secured, came open and separated at the hinge line.

The door was struck by the left propeller, damaging the blades. The door became lodged on the leading edge of the left wing and the pilot abandoned the take-off. The subsequent landing was heavy.

In addition to the damage caused by the door, the wings were twisted and the lower wing skins rippled during the heavy landing.

On arrival overhead the destination the pilot assessed the wind velocity and decided to land on runway 23, a 610 metre long grass strip. The wind direction was north-north-easterly at 15 knots.

The pilot reported that the aircraft touched down further along the strip than normal, and that braking was poor on the grass surface. About two thirds of the way along the strip he considered going around but did not attempt to do so because of trees at the end of the strip. The aircraft overran the strip and collided with an abandoned vehicle before overturning.

The pilot had inadvertently misread the wind direction, and in doing so had operated the aircraft outside the published landing performance criteria.

The aircraft taxied for runway 27 at Jabiru for a flight to Darwin. There was light rain on the threshold of runway 09 and a wind velocity of approximately 290 degrees at 10 knots with active thunderstorms approaching from the east.

After take-off, the aircraft climbed normally until about 100 feet above ground level, then began to sink. Full power was being indicated on the engine instruments for both engines. However, the pilot noticed that the airspeed was decreasing. He set the best rate of climb speed and selected the landing gear up to reduce drag. The aircraft continued to descend until it struck the runway. It slid along the runway for about 200 metres before stopping. The pilot and passengers vacated the aircraft uninjured.

A witness noticed a wind shift as the aircraft commenced its take-off and it is possible that the aircraft encountered a microburst just after liftoff.

The aircraft, a Sea scan version of the Westwind 1124, was departing for a normal coast watch operational flight. The outside air temperature (OAT) was 30 degrees C, with a north westerly wind at 5 kt. It was loaded to its maximum all up weight (MAUW) and configured for a flapless take-off. This being normal requirements for the aircraft operating at MAUW with an OAT greater than 28 degrees C. The calculated V1 speed was 140 kt, and the VR speed 148 kt.

With the co-pilot at the controls the aircraft taxied the 4 km to the threshold of runway 29 for departure. The take-off run was normal until the aircraft had travelled approximately 2,000 m and accelerated to 128 kt. At this point the left main wheel tyre suffered a blow out causing the aircraft to veer left.

The captain took control and rejected the take-off. Whilst he was attempting to maintain directional control, using brakes and nose wheel steering, the right main wheel tyre also blew out and the aircraft swung to the right, departing the runway and coming to a stop on the flight strip in the reciprocal direction to the take-off.

The left main gear leg collapsed, and the aircraft suffered damage to the left gear attachment structure, left fuel tank cell, and the infra-red dome mounted to the lower fuselage surface. All occupants evacuated safely.

The left main wheel and tyre remains were examined at the CAA Materials Evaluation Facility. The examination revealed that all three fusible plugs in the wheel hub were loose. Although it could not be established if the fusible plugs were tight before the accident, enquires indicated that they had not been touched by any other party prior to the wheel coming into BASI's possession.

The valve, and gasket between the wheel hub halves, were in good condition, and no flaws or defects were found in the tyre material, or its manufacturing process. An uneven wear pattern across the tread was noted, being more advanced on the middle tread and shoulders than on the intervening sections of tread.

The wear along the tyre shoulders is consistent with under-inflation, but as there was also some wear on the middle tread it was apparent that the tyre had been correctly, or possibly over inflated at some time. Over a period of time an undetected slow leak had probably occurred, with the wear pattern indicating that the tyre had been under-inflated for a number of take-offs and landings. In this condition the sidewalls would have been subjected to increased flexing, resulting in excessive heat generation and delamination between the fabric layers. Eventually the tyre would have been unable to sustain these flexing loads, resulting in rapid deflation and shredding of the tyre from the wheel. The aircraft operating at MAUW, the hot tarmac, and long taxiing distance would have exacerbated the situation.

The reason why the fusible plugs were loose could not be determined, but this was considered as the most probable source of the slow leak.

The pilot reported that during the descent into Fitzroy Crossing he diverted to inspect a fishing pool. During the inspection the descent continued unnoticed, and the aircraft collided with an object, later identified as a power line. The aircraft continued to operate normally and landed safely at Fitzroy Crossing.

Whilst conducting pilot training for Search and Rescue helibox dropping, the helibox hit the tail of the leading edge of the horizontal stabiliser. The heliboxes were being dropped out of the front passenger window of the aircraft. The drop was the last for the day and there had been no problems experienced in the previous drops. Turbulence in the area had built up during the day and was causing slight airspeed and altitude fluctuations. CAA manuals recognise that turbulence can cause an increased risk of tailstrike in this type of operation and advise to exercise caution when turbulence is present.

While conducting a pleasure flight the aircraft right rear landing wire failed. The pilot returned to TYABB and landed normally.

The landing wire examination found that the wire failed in fatigue initiating from two subsurface defects in approximately the middle of the wire length.

A sample taken some 40 mm from the fracture surface contained intermetallic stringers reducing the integrity of the material. Size of the stringers was consistent with the size of the subsurface defects. The analysis identified the stringers to be an aluminium based intermetallic, possibly from the refractory material used in production of the material.

The material composition and microstructure was typical of a drawn and rolled 316 stainless steel. The manufacturer advised the wire was made of 316S16 steel.