Private Australian

Inspection of the engine determined that it was capable of developing full power at the time of the accident. The throttle cable was found to have separated from the cast bronze throttle control lever at the fuel/air metering unit on the intake manifold. The serrated steel bush in the throttle control lever at the cable attachment had become loose, causing the hole to wear elongated which reduced the edge distance from the hole to the end of the control lever sufficiently for it to fail when the throttle was opened. This probably occurred during the last takeoff. During flight, the bush, which was still attached to the cable ball end by the bolt, was probably in such a position as to operate the lever when the throttle control was moved to reduce power for climb and cruise. As the flight progressed and the cable separated from the lever, in-flight movement and vibration would have moved the throttle towards the closed position, with the subsequent reduction in power. Further inspection found that the assembly of the cable to the lever was incorrect, with the washer from under the bolt head being omitted. This reduced the bearing area at the bolt head to the control lever, with the possibility that the bolt may have only been clamped to the bush assisting any movement of the bush in the lever. Once the steel bush started moving in the softer bronze material the rate of wear would have been rapid. The aircraft had flown 85 hours since the last periodic inspection, at which time it may have been possible to detect the first signs of wear between the bush and the control lever if information advising of this type of fault had been available.
The following factors were considered relevant to the development of the accident:
- Incorrect assembly of the washers on the control cable attachment bolt may have allowed the bush to start moving in the lever.
- The bush became loose in the control lever, with the subsequent wear elongating the hole allowing the control lever end to fail.
- The throttle control cable separated from the throttle control lever.
- The throttle closed sufficiently during flight to reduce engine power.
- The aircraft was too heavy to maintain flight.
- The aircraft was operating over an area unsuitable for a forced landing.
- Wear between the bush and the lever may have been detectable during the previous periodic inspection if advisory information had been available.

The circumstances leading to the development of this accident could not be established conclusively. However, the evidence supports the following as probable factors:
- The pilot might not have been aware of the human factors aspects associated with dark night take-offs.
- The pilot could have been influenced by stress and/or fatigue.
- The aircraft was taking off towards dark textureless terrain and no visible horizon.
- By transmitting his airborne call very soon after lift-off, the pilot was not devoting his full attention to flying the aircraft.
- The pilot became disoriented and placed the aircraft in a shallow descent as it accelerated after take-off.

It was determined that the Captain had made some miscalculations in his pre-flight assessments. He had noted the landing distance available as being the same for both runways, whereas runway 28 has a reduced length due to terrain clearance requirements on the approach. Under the conditions both forecast and prevailing, and using the criteria applicable at the time for an aircraft fitted with an alternate means of retardation, i.e. drag chute, the landing distances required for both runways were greater than the landing distances available. The Captain had also evidently applied incorrect techniques during the landing. He had not attempted to deploy the drag chute immediately the nose wheel was on the ground, and had not applied unmodulated pressure to the anti-skid braking system. These measures are required by the manufacturer to obtain maximum performance. It was found that the drag chute canister lid had been sealed with tank sealant and painted over. The latch assembly had operated but the drogue chute spring was insufficiently strong to break the seal. When the sealant was prised away from around the lid, the system operated normally. This error had not been found during a check of the aircraft immediately following repainting. The lid had the appearance of an oblong radio antenna and was not marked in any distinguishing manner. The problem should also have been noticed during a subsequent inspection of the drag chute for moisture. The inspection is required every 90 days if the drag chute has
not been deployed, and requires the removal of the lid and drogue chute in order to feel the main chute for moisture. The condition of the sealant would indicate that this had not been carried out.
The following factors were considered relevant to the development of the accident:
- Inadequate pre-flight planning and preparation by the flight crew. The runway distance required was in excess of the distance available on either runway.
- Adverse runway and weather conditions - wet surface and downwind component.
- Improper sealing of drag chute canister.
- Inadequate maintenance of the drag chute system.
- Improper operation of wheel brakes.

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.

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.

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.

No fault was found with the aircraft or its systems which might have contributed to the accident. It could not be determined who was manipulating the controls of the aircraft at the time of the accident. Evidence was obtained that it was the habit of the check pilot to have pilots undergoing endorsement or check to fly two circuits landing into wind and then to carry out crosswind landings. The check pilot and the pilot under check had previously operated at the dam and alighted on to both the east/west and the north/south channels. Having been observed to fly two into wind circuits and then head north and not be sighted again, it is possible that the aircraft then commenced crosswind operations onto the north/south arm of the lake, landing in a southerly direction with a crosswind from the left. Information from the Bureau of Meteorology indicated that the surface wind in the area at the time of the accident was 090` magnetic at 15 knots. This information was confirmed by witnesses at the dam wall who observed white caps on the surface of the dam. The north/south channel of the lake was bounded on its east side by steep hills rising to 70 metres above water level. The effect of this high ground was to partially blanket the north/south channel from the easterly wind. The position of the wreckage was in the area where the wind shadow effect would have ended and where the wind would have blown at full strength along the main east/west channel of the lake. The crosswind limitation for the aircraft as stated in the flight manual was 8.7 knots. Commenting in early 1988 on an enquiry regarding the raising of this limit, the aircraft manufacturer emphasised the 8.7 knot limit and advised that any test work to raise the limit should proceed cautiously starting at or below the current (8.7 knot) limit. If the aircraft was conducting crosswind operations in the north/south channel, and suddenly encountered a 15 knot crosswind on exiting the wind shadow area, the control difficulties confronting the pilot could have been significant. The aircraft wreckage was intact except for the floats which had been torn off by water impact forces. The right float was severely damaged while the left was intact. The forward tip of the right float had been severed by the propeller. The remaining forward section had then been forced upwards and outboard and had broken off. This weakened the float support structure, causing it to fail, and allowing the remaining section of the right float to strike the right side of the fuselage just aft of the cabin. Damage of this type an magnitude was most probably caused by the nose of the right float digging into the surface of the lake at relatively high speed. For this to occur, the aircraft was banked to the right at float impact - a possible consequence of encountering a strong crosswind from the left. There was no evidence that the aircraft had hit a submerged object. The factors associated with the development of this accident could not be determined.

The pilot has no recollection of events immediately prior to the accident. There is no indication that the aircraft was not functioning normally at the time of the accident. The weather was fine, there was a light northerly breeze, and there was no moonlight. Indications are that the pilot may have become disorientated whilst attempting to carry out a visual circuit when there was no visual horizon. The landing area did not meet the requirements for night operations published in the Visual Flight Guide.
The following factor was considered relevant to the development of the accident:
The pilot was attempting to carry out a night visual circuit when there was no visual horizon.

Although the investigation was hampered by the extensive fire damage, no defect or malfunction was discovered which might have contributed to the accident. The reason the pilot, who had extensive agricultural experience, chose to conduct swath runs towards steeply rising ground was not determined. The wind direction had changed since the previous day, and the aircraft was likely to have been affected by downdrafts on the lee side of the hills. When the pilot realised the aircraft was not performing as expected, he evidently attempted to dump the remaining load and reverse the direction. However, there was insufficient aircraft performance available to successfully complete this manoeuvre.
Significant Factors:
The following factors were considered to be relevant to the development of the accident:
1. The pilot elected to conduct spreading runs towards steeply rising ground, when safer alternatives were available.
2. It was likely that downdraft conditions existed on the lee side of the hills.
3. The pilot evidently misjudged the climb performance of the aircraft.
4. The pilot delayed attempting a reversal of direction beyond the point where such a manoeuvre could be safely accomplished.

A thorough examination of the aircraft wreckage did not reveal any malfunction or mechanical failure which may have caused a sudden and severe loss of control. Investigation showed that at the
moment of impact the aircraft was in a near vertical descent, without any rotation about the vertical axis, and the wings were in a stalled condition. No reason was found which could have explained either the low flying, or the steep pull-up. During the investigation it was established that with this aircraft type, a considerable degree of sustained elevator force would need to be applied by a pilot in order to achieve the type of flight path reported by the witness. It is considered that such a control input would need to be deliberately executed.
Significant Factors:
It was considered that the following factors were relevant to the development of the accident:
1. The pilot, or passenger, performed what was apparently a deliberate steep pull-up from low-level. The reason for the pull-up was not established.
2. Loss of control occurred as a consequence of the aircraft becoming stalled.
3. There was insufficient height for the pilot to effect recovery following the loss of control.