Australia

The following findings were reported:
- The pilot did not have recent experience in high-performance, high-altitude aircraft except for the 51.7 hours gained in the MU-2.
- The pilot did not possess some of the experience levels and recency requirements placed on MU-2 pilots immediately after the accident by the CAA.
- The pilot did not take sufficient account of the operational characteristics of this aircraft type.
- The pilot's situational awareness was probably impaired during the flight, because of the combination of pre-existing cumulative fatigue, and insufficient sleep in the previous 42 hours.
- The meteorological conditions were conducive to the formation of airframe icing on an aircraft flying in cloud along the flight planned route.
- It is probable that control was lost as the aircraft banked to the left over Meekatharra, to change track towards Port Hedland.
- The pilot reported that the aircraft was in ice during his last radio transmission.
- The pilot was unable to recover from the spin before the aircraft hit the ground.

On-site examination of the aircraft and subsequent laboratory examination and testing of components did not reveal any pre-existing mechanical defects or abnormalities which could be considered as factors in, or contributory to, this accident. Powerline impact marks on the aircraft were consistent with the aircraft being in a left banked attitude when it struck the wire. The investigation revealed that the loader driver's truck bucket load gauge had no conversion/calibration chart, and that the aircraft was being operated in excess of the maximum allowable weight for takeoff. It is considered probable that the pilot had elected to fly down the valley, (thus taking advantage of the downslope), to compensate for a degradation of aircraft performance whilst operating overweight in the changed ambient conditions. The absence of a superphosphate trail before wire impact indicates that the pilot did not dump any of the load and was either unaware
of, or had forgotten about, the existence of powerlines to the south-west of the marked powerpole.
The following factors were considered relevant to the development of the accident:
1. The aircraft was being operated in an overweight configuration for takeoff.
2. The pilot did not adjust the takeoff weight of the aircraft to give an acceptable climb performance.
3. The pilot was unaware of, or had forgotten about, the powerlines to the south-west of the marked pole; or,
4. the pilot misjudged the clearance between the powerlines and the aircraft whilst trying to overfly them.

Because of the destruction of the aircraft by the ensuing fire the status of the seat belt assemblies were unable to be determined. The investigation revealed that both engines were operating at high power at the time of impact. No malfunction or defect could be found with the aircraft which could have contributed to the accident. The survey task required the pilot to adhere strictly to a particular track and the target height for the flight was 500 feet above ground level while maintaining visual contact with the ground at all times. The pilot was suitably qualified to act as pilot in command of survey operations down to a height of 200 feet above ground level. The investigation concluded that the aircraft was being operated at a height substantially lower that 500 feet above ground level prior to the accident. Impact marks, wreckage and mechanical evidence suggest that the aircraft impacted terrain at a time when the pilot was attempting to carry out an evasive manoeuvre to remain clear of terrain. The reason why the aircraft was being operated at such a height and why the pilot delayed turning away from the steeply rising terrain could not be determined.
The following factors were reported:
- The pilot continued the flight into adverse weather conditions.
- The pilot flew the aircraft towards steeply rising terrain at a height substantially lower that 500 feet above ground level.

No aircraft defects were found which may have been factors in the accident. The investigation indicates that the pilot attempted to fly under the low cloud base, in order to reach the Port Welshpool destination where weather conditions were earlier reported to have been partially sunny. Port Welshpool is not serviced by an approved navigation aid. The pilot attempted to descend below the cloud base, hoping to achieve visual flight conditions to continue to his destination.

Two main hypothesis were proposed. One was that the pilot was distracted from a less than demanding task by business worries. The other was that the pilot had perceived that the SWER line was on the right of the windmill and outside the fence and therefore did not present an obstacle to his procedure turn. Neither hypothesis could be substantiated. An additional concern was the fact that the pilot had died from impact injuries in an accident that, prima facie, was survivable. Concern focused on whether the pilot had secured his harness properly and/or whether the inertia reel had failed. Detailed engineering inspection of the inertia reel by the Bureau and the manufacturer could not positively determine the mode of operation of the inertia reel. However, the post mortem report showed that the nature of injuries to the pilot, while sufficient to cause death prior to the fire, were such as to indicate that the inertia reel had probably not failed. The pilot did not see the powerline in time to avoid a collision.

The landing gear problem arose when the left main landing gear would not lower. Examination of the aircraft revealed that both hinges fitted to the inboard landing gear door had fractured. The forward hinge had fractured as a result of fatigue and the rear hinge as a result of overload. The fatigue crack initiation had occurred at a sharp edged, prominent forging flash on the inner radius of the hinge and had grown over approximately 4000 load cycles. A similar fatigue problem had been identified on an earlier version of the hinge (part number 46653-00), however, regular inspections for fatigue cracking were discontinued when hinges with part number 47529-32 (as fitted to VH-DEG) were introduced in 1980. Similar fatigue cracking was found in the forward door hinge of another PA31 during the investigation. The fractured hinges jammed the left main landing gear mechanism and neither the normal or emergency extension systems could extend the gear. The pilot was apprehensive about wheels up landings. Much of his decision making was aimed at reducing the risk of fire and minimising the damage the aircraft would sustain during the landing. eg. Selection of a dirt runway instead of the sealed strip, landing with flaps retracted etc. During the pilot's attempts to rectify the landing gear problem, and up until the time of his touchdown, he was subjected to considerable radio transmission traffic involving questions, directions and suggestions which distracted him from his primary tasks. The pilot indicated on at least two occasions that he was ready to land, however, each time advice and questions from the ground personnel involved overrode his intentions. When the pilot was asked if he wanted a flare path on runway 27 there was still some natural light available and he was intending to land. However, by the time he was able to make his final approach it was dark and he was unable to see the ground. Studies have shown that aircrew subjected to high levels of stress can suffer skill fatigue and cognitive task saturation, which in turn can lead to a breakdown in the decision making process. It was apparent from the pilot's radio transmissions and the quality of the decisions made in the latter part of the flight that his information processing and decision making abilities had been degraded by the stress of continuous radio transmissions and continuous, and sometimes conflicting, instructions. As a result, what should have been a relatively simple wheels up landing in daylight was turned into an extremely difficult wheels up landing at night. With the landing gear retracted the aircraft's taxi and landing lights were not available to the pilot.
The following factors were considered relevant to the development of the accident:
1. Manufacturing defect. A forging flash created a stress concentration which led to fatigue cracking.
2. Inadequate inspection procedures. Previous inspection procedures introduced to disclose similar cracking were withdrawn on the introduction of later part numbered hinges.
3. Apprehension of the pilot. The pilot was apprehensive about apparently significant dangers of landing an aircraft, wheels up, on a sealed runway.
4. Inordinate interference in aircraft operations by ground based advisors. The ground advisors input overrode the pilot's decision on a number of occasions with the result that a simple exercise became very complicated.
5. Cognitive task saturation and skill fatigue. The amount of information, advice and suggestions being passed via the radio communications system overloaded the pilot decision making abilities.
6. Improper in-flight decisions. As a result of task saturation the final decision made by the pilot to attempt a night landing on an unlighted strip was incorrect.
7. The pilot did not see and therefore was unable to avoid the levy bank.

The exact cause of the accident could not be determined.

The following factors were considered relevant to the development of the accident:
1. The pilot selected the incorrect takeoff direction for the wind conditions prevailing.
2. The pilot continued the takeoff into an area of unsuitable swell. This accident was not the subject of an on-scene investigation.

The pilot declined to provide any information which might have clarified the circumstances of the accident, however, available information indicates that he carried out an unauthorized low pass over the boat. During the turn following the low pass, he misjudged the aircraft's height and the right wing tip struck the water.
The following factors were considered relevant to the development of the accident:
- The pilot was neither trained nor authorized to conduct operations at low level,
- The pilot exercised poor judgement by operating at an unnecessarily low height,
- The pilot misjudged his height above the water.

The reason why the aircraft flew into the sea could not be determined.