Oceania

It is probable that the pilot did not have an adequate understanding of the operations of the MU-2B-60 aircraft at high altitude. The meteorological conditions were conducive to the formation of ice on aircraft flying in cloud above the freezing level. It is probable that loss of control occurred above the freezing level on climb to an amended altitude of FL 210.

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 subsequent investigation established that the flight crew were properly qualified to conduct the flight, and that the aircraft was appropriately certified and maintained. The flight was conducted in accordance with the conditions of the operating contract. At the time of the occurrence the aircraft had not deployed the sleeve target and no firing was being carried out. No evidence was found to suggest an in-flight structural failure or fire. The installation of the target towing equipment was not considered to have been a factor in the development of the accident. There was a loss of control of the aircraft following an apparent engine malfunction. The precise reasons for the accident have not been established.
The following factors were considered relevant to the development of the accident:
1. Apparent engine failure or malfunction.
2. Control of the aircraft was lost for reasons which have not been determined.

A detailed examination of the aircraft and its systems failed to reveal any defect which could have contributed to the accident. The engine was operating at high power at the time of the impact. It is probable that the pilot forgot about the presence of the powerlines. It was noted that the pilot was not wearing a shoulder harness and that an unapproved modification had been made to the lap harness. The toggle fitted to the lap harness was a type approved for 9 to 12g applications only and therefore was not suitable for agricultural operations, which require equipment capable of withstanding 25g loads.
The following factor was considered relevant to the development of the accident:
1. The pilot did not see or avoid the powerline.

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.

Examination of the wreckage was severely hampered by the extreme fire damage sustained, but no evidence was found of any defects that might have contributed to the accident. The aircraft had evidently been under control at the time it collided with the trees. A post analysis of the conditions by the Bureau of Meteorology indicated the possible presence of strong up and down drafts, horizontal wind shear, turbulence, and estimated visibility as 2-3000 metres in rain. The evidence suggested that the pilot may have been lower than he believed as the aircraft overflew the
aerodrome. Having passed overhead, there there would have been few external visual references under the existing conditions to alert him that the aircraft was inadvertently being descended into the ground.
Significant Factors:
The following factors were considered relevant to the development of the accident:
1. The pilot attempted to conduct an operation for which he was not qualified.
2. Severe weather conditions in the destination aerodrome area with strong winds, turbulence, heavy rain and poor visibility.
3. The pilot continued flight into adverse weather conditions.
4. The pilot may have misread his altimeter and been lower than intended.
5. The pilot may have unintentionally descended the aircraft into the ground in conditions of poor visibility.