Jump to Content

Analysis

Summary

The flight

The flight apparently proceeded normally until late final approach when the pilot initiated a go-around because of a vehicle on the airstrip. There were clear indications from the wreckage examination that the aircraft was rolling and yawing left at impact. The status of the left engine at impact logically supported such aircraft behaviour. While the witness description of the aircraft initially veering left also supported this conclusion, the report that the aircraft rolled right immediately before impact did not. In the asymmetric power and low speed situation that existed, it was most unlikely that the aircraft could have rolled right. On balance, therefore, the direction of roll as recalled by the witnesses was incorrect.

Whether the vehicle entered the airstrip during the latter stage of the aircraft's approach, or whether it was on the airstrip and the pilot expected it to move, was not determined. However, the position of the wing flaps at impact suggested that the pilot had selected full flap, and that the flaps subsequently did not move from this position. This implied that the pilot had been committed to land and that the aircraft speed was at, or less than, 65 kts.

Under normal circumstances, a go-around with both engines operating would have been a relatively basic procedure for the pilot to conduct. Because there was no apparent earlier action or radio call, it is unlikely that the pilot was aware of an asymmetric engine condition until the go-around was initiated. When the asymmetric power condition arose, the pilot's task was complicated by a number of aspects:

  1. the aircraft was at low level, and probably low speed, when the go-around was initiated. This would have provided minimal opportunity for the pilot to lower the nose of the aircraft to increase airspeed and hence aircraft controllability;
  2. depending on the exact position of the aircraft when the go-around was initiated, the pilot may have had to manoeuvre away from the sand dune and coconut palms on the southern side of the strip;
  3. the pilot had to deal with the control forces associated with the asymmetric power condition, in addition to those associated with the engine power increase;
  4. to retract the flaps to the take-off position, feather the left propeller, and adjust the elevator and rudder trims would have required the pilot to fly the aircraft with her left hand while conducting these other tasks with her right hand. Completion of these tasks may have been difficult, if not impossible, in that control of the aircraft may have required the pilot to use two hands on the control yoke to overcome the out-of-trim forces;
  5. the pilot's stature, seating position as altered by the cushions she normally used, and the position to which the rudder pedals had been adjusted, may have affected her ability to manipulate the aircraft controls to the extent necessary to maintain control of the aircraft;
  6. at a speed of 60 kts, the aircraft would have taken about 7 seconds to travel from overhead the witnesses at the eastern end of the island direct to the impact position. While the actual aircraft track was not established, this timeframe was probably indicative of the period available for the pilot to recognise the situation, evaluate available options, decide what action should be taken, and initiate that action; and
  7. the north-westerly wind would have exacerbated any tendency for the aircraft to drift left as a result of the asymmetric power situation.

These influences would have placed the pilot under an extreme combination of workload and stress and may have affected her decision-making and flying ability.

An alternative course of action available to the pilot was to overfly the vehicle and land the aircraft on the remaining section of strip. Another was to reduce power on the right engine and conduct an emergency landing on the tidal flat area. However, without accurate information concerning the position and altitude of the aircraft when the go-around was initiated, no positive conclusions could be drawn concerning these options.

Wreckage examination

The pre-impact position of the carburettor heat controls for both engines could not be positively determined. It is possible for ice to have formed in one carburettor and not the other. If ice was present in the left engine carburettor during the approach, it was unlikely to have been evident to the pilot because the engine was probably operating at low power. Such a condition could have caused the engine to fail to respond at the commencement of the go-around. Because of the salt water corrosion damage, it was not possible to assess the pre-accident condition of the carburettor. It is also possible that aggressive throttle operation by the pilot at the commencement of the go-around could have affected normal engine operation. In summary, there was insufficient evidence to reach a positive conclusion concerning the operation of the left engine.

Examination of the aircraft wreckage did not reveal any evidence to link the circumstances of the accident with the defects listed in ASR 111642, or those subsequently rectified on 2 January 1999. Further, no evidence was found of any aircraft unserviceability being reported and/or recorded between 2 January and the accident flight.

 
Share this page Comment