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Analysis

Summary

Preparation for takeoff

The pilot was qualified, appropriately endorsed and reported to be fit and well for the flight. The available aircraft and maintenance documentation, results of the recent 50-hourly inspection and subsequent engine ground run, and the successful 2 hour flight to El Questro indicated that there were no known pre-existing aircraft anomalies that might have contributed to the occurrence.

Although it was reported that the pilot most likely observed the El Questro Aircraft Landing Area (ALA) in June 2003, the investigation was unable to determine the means by which the pilot satisfied himself prior to arriving on 28 August 2004 that the ALA was suitable for his operation in accordance with the requirements of Civil Aviation Regulation 92. The runway width and length satisfied the guidance provided by Civil Aviation Advisory Publication (CAAP) 92-1(1) for the aircraft. While the tree that was initially struck by the aircraft may have infringed the lateral transitional slope, the pilot had indicated his acceptance of the suitability of the ALA for his operation and had landed without incident on 28 August 2004.

The results of the fuel tests, and the large number of other aircraft that had also used the Broome fuel supply without any reported problems, indicated that the quality of that fuel supply had not contributed to the development of the occurrence. The reported conduct by the pilot of the left underwing fuel drain test and observed presence of the pilot underneath the right wing tended to suggest that the pilot had completed the fuel drain and sump checks. That supported the consistent reports from all witnesses that the aircraft's engines sounded 'normal' throughout the takeoff, and decreased the likelihood that water or other particulate contamination of the aircraft's fuel supply to the engines had any effect during the takeoff.

The pilot's extensive and recent experience in the operation of this type of aircraft, and apparent intimate knowledge of its systems and procedures, would have reduced the likelihood of the pilot omitting to unlock the aircraft's controls prior to commencing the takeoff. In any case, the ability of the pilot to fly the aircraft from the runway meant that the control column and optional rudder gust locks were unlocked at that time. Therefore, the pilot should have been able to react to the reported initially slight left bank after takeoff.

The Broome engineer's report that the engines had started and run normally after the 50-hourly inspection, and the lack of any indication by the pilot during his stay at El Questro of any problems affecting the flight to El Questro indicated that the aircraft probably did not have a recurring engine starting problem. The action by the pilot to continue the engines start, taxi and takeoff without interruption indicated that the pilot was unconcerned by the reported initial difficulty starting the left engine, or by the 'frequency vibration' that was reported by the passenger witnesses at the runway 32 parking area. In addition, given the history of extensive efforts by the pilot during the flight to Australia to at all times ensure the serviceability of the aircraft, it was likely that the pilot would have attended to any engine(s) start or after-start anomaly as soon as it became evident. The investigation concluded that the start and after-start passenger witness reports probably resulted from observations that were accepted as 'normal' by the pilot and also by the pilot witness who was also located at the runway 32 parking area.

Takeoff

The action to conduct a rolling takeoff was consistent with an attempt by the pilot to minimise the potential for damage to the propeller blades and underside of the aircraft as a result of the dislodgement from the runway surface of pebbles and other potentially damaging debris. The investigation considered whether the pilot may have attempted to lift off the runway earlier than normal in an attempt to minimise the possibility of such damage. However, this was considered unlikely given the report from the pilot witness, that the lift-off appeared to reflect other twin-engine aircraft takeoffs that he had observed, and the approximation of the length of the take-off roll to that predicted by the Pilot's Operating Handbook (POH) performance charts.

The reports from the witnesses at the runway 32 parking area that there had been no smoke or fumes observed emanating from the aircraft and that nothing fell from it during the takeoff, corroborated the results of the after-accident runway inspection. That, along with the identification of all control surfaces at the accident site, and the distribution of the aircraft wreckage, indicated that there had been no aircraft break-up or detachment of the aircraft's control surfaces prior to the impact with the trees and ground.

There was no evidence of any pre-existing failure or anomaly in either engine or their supporting assemblies or components that were able to be tested, that might have adversely influenced the performance of the engines during the takeoff. In addition, the nature of the damage to the propellers and propeller hubs was consistent with the delivery of comparable amounts of power to both propellers from within the engines' upper operating range at the time of ground impact. There was no evidence of an enduring power failure of either engine during the takeoff.

The investigation considered a number of possible factors that could have had the potential to affect the lateral control of the aircraft. Those factors included: the possibility of a lateral weight imbalance; an aerodynamic influence on the performance of the aircraft; and whether the pilot might have either intentionally or inadvertently manoeuvred the aircraft to the left of the runway immediately after lift-off.

Given that all of the baggage was observed being stowed in the aircraft cabin, there was minimal potential for the baggage distribution on takeoff to have adversely affected the lateral control of the aircraft. The pilot's high and recent experience operating the aircraft minimised the possibility that he might have neglected to check the correct engine fuel selections on the three occasions (at least) required by the POH during the flight to El Questro. Similarly, had the pilot inadvertently mis-selected the engines' fuel supply, the nature of the aircraft checks meant that it was unlikely that a mis-selection would remain undetected by the pilot for the duration of the flight to El Questro. Therefore, it was considered that the potential for a lateral fuel load imbalance, and therefore aircraft weight imbalance to have developed during the flight to El Questro was minimal.

In any case, given the short taxi to runway 32 from the parking area and the rolling takeoff, any disparity that may have existed in the lateral fuel distribution for the takeoff was estimated to have been within 50 pounds of that for the landing at El Questro. That meant that the pilot would have been aware of the potential for any associated aircraft roll during the takeoff and would have been ready to compensate. In addition, as indicated in the POH, the relatively benign nature of the ambient conditions and reported 'normal' appearance of the takeoff ought to have allowed the pilot to control the aircraft even had there been a lateral fuel imbalance.

The aerodynamic factors with the potential to have affected the lateral control of the aircraft included the effects of asymmetric or 'split' flap and a wing stall. The damage to the left flap meant that, in the first instance, the investigation could not discount that split flap might have occurred during the lift-off. However, given that the right flap was confirmed retracted at ground impact, the only possibility was that the left flap might have self-extended. In that case, the aircraft would have rolled to the right after lift-off. That was not consistent with the witness reports that the aircraft banked to the left after lift-off before striking the trees to the left of the runway. On that basis, the investigation discounted that split flaps had occurred.

It was considered most likely that the experienced and proficient pilot would have raised the nose wheel at 95 knots indicated air speed (KIAS) and lifted the aircraft from the runway at 100 KIAS in accordance with the procedures recommended in the POH.

The pilot witness's description of the takeoff and initial slight left bank after takeoff could be construed as normal manoeuvring. In that case, and given the reported lack of a very steep pitch angle after takeoff, it ought to have been difficult for the pilot to have stalled the aircraft. In addition, the pilot's high experience and proficiency in the aircraft, and intimate knowledge of its systems meant that it was highly unlikely that he might have: allowed the speed to decrease to between about 88 to 93 KIAS in order for the stall warning to have activated; to have then reacted inappropriately, or not at all to that warning; to have finally not, or inappropriately, reacted to any developing mild and then increasing aerodynamic buffet; and, instead allowed a continuing reduction in airspeed until reaching about 83 KIAS whereupon the aircraft stalled. On that basis, it was concluded that an aerodynamic stall had most likely not occurred.

Given the pilot's predominant recent experience during the flight to Australia of landing and taking off from major or international aerodromes, the occurrence takeoff was potentially his first from an airstrip and surface such as that at the El Questro ALA for some time. In addition, as a result of the pilot having landed the aircraft on runway 14, the takeoff from runway 32 was potentially his first opportunity to have comprehended the relative proximity of the trees to the left of the runway. That comprehension was probably only possible during the conduct of the occurrence takeoff and may have influenced the pilot's awareness of the need to maintain the aircraft overhead the runway centreline during the takeoff.

The absence of bird or other animal remains along the runway surface, and the reported absence of any thermal activity or dust devils, indicated that the pilot most likely was not required to intentionally manoeuvre the aircraft as a result of those potential influences on the takeoff. Also, the nature of the pilot's recent flying experience, the number and variety of the exotic locations visited during his flight to Australia, the pilot's age and total flying experience, and his probable desire to not compound any apprehension on the part of the passenger meant that it was most unlikely that the pilot was performing the early stages of any sort of intentional low-level manoeuvre.

The investigation could not discount that the pilot might have been momentarily distracted during the lift-off from the runway to the extent that the aircraft developed an unintended slight left bank and drift. The probable small amount of time for the pilot to have reacted once he perceived any unintended movement of the aircraft would have minimised the possibility for the pilot to have avoided impacting the trees to the left of the runway.

Summary

There was no documentary, physical or witness evidence identified during the investigation that indicated that an anomaly or failure in the aircraft or its systems contributed to the development of the occurrence. In addition, there was no evidence to indicate that the reported slight left bank after lift-off from the runway was the result of a lateral imbalance of the aircraft, an aerodynamic effect or an intentional control input by the pilot. However, the investigation was unable to determine whether the pilot might have been distracted during the lift-off by an unidentified event to the extent that he did not notice, or was unable to react to any unintentional left bank and drift of the aircraft in sufficient time to prevent the aircraft impacting the trees to the left of the runway.

CONCLUSIONS

Findings

Pilot

  • The pilot was qualified and appropriately endorsed for the flight.
  • The pilot was reported to have 975 hours experience flying the Cessna 421 B and C models over the preceding 10 year period and at least 2,100 total flying hours.
  • The pilot held a valid Class 2 medical certificate.
  • The pilot was reported to be fit and well and in good spirits prior to the flight.
  • There was no evidence of any pre-existing medical disease, sudden illness or incapacitation that may have affected the pilot's ability to control the aircraft.

Aircraft

  • Export Certificate of Airworthiness number 3588/04 was issued for the Swiss-registered aircraft by Swiss regulatory authorities on 27 February 2004.
  • The quality of the fuel that was supplied from the Broome supplier was not a factor in the occurrence.
  • There was sufficient fuel onboard the aircraft to complete the flight to Broome.
  • The aircraft weight and balance was estimated to be within the published limits at the time of the takeoff.
  • The ability of the pilot to lift the aircraft from the runway meant that the control column lock and optional rudder gust lock were unlocked at that time.
  • There was no break-up of the aircraft or detachment of the aircraft's control surfaces prior to the impact with the trees and ground at the accident site.
  • There was no evidence of any pre-existing failure or anomaly in either engine or their supporting assemblies or components.
  • Comparable amounts of power were being delivered to both propellers from within both engines' upper operating range when the aircraft impacted the ground.

Other findings

  • Witness reports indicated that, shortly after lift-off from the runway, the aircraft banked and drifted to the left slightly, before striking the trees to the side of the runway and impacting the ground.
  • There was no evidence that the ambient conditions contributed to the circumstances of the occurrence.
  • The pilot indicated that the El Questro ALA was suitable for his operation.
  • There was no distress radio transmission by the pilot.
  • Based on the available evidence, it was considered most unlikely that the pilot was performing the early stages of any sort of intentional low-level manoeuvre.
  • The investigation could not discount that the pilot might have been momentarily distracted during the lift-off, resulting in the development of an unintentional slight left bank and drift of the aircraft.
  • The relative proximity of the trees to the left of the runway would have adversely affected the time available for the pilot to have reacted to the development of any unintentional left bank and drift.
  • The destruction of the aircraft cockpit and cabin from the combined effects of the impact forces and post-impact fire rendered the accident non-survivable.
 
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