Below is a list of conclusions from the official investigation. I think it is correct to post the list here, as the accident has been discussed much and the stories we find from the internet about really do not give a proper picture of this crash. Thanks to Rob Osborne (Great Ozzie) for providing the necessary information!
Findings
- 1.
The occurrence aircraft was operating under an EXPERIMENTAL category of CAR 4b; the aircraft had acquired an accumulated flight time of 23 hours in its modified configuration.
2.
The aircraft was loaded within the weight and balance constraints published in the Aircraft Flight Manual.
3.
The aileron and elevator trim tabs were near their neutral positions.
4.
No flight control check was observed prior to commencement of the take-off roll.
5.
The take-off ground run was 20 per cent longer than the performance charts predict.
6.
Aft elevator authority existed at rotation.
7.
The aircraft's initial climb attitude was significantly higher than on previous take-offs under similar environmental conditions.
8.
At approximately 35 feet agl, the aircraft made a noticeable pitch-up movement; from that point onwards, the elevator control surfaces remained in their neutral position.
9.
Airspeed remained above the stall speed throughout the in-flight manoeuvre.
10.
The flight control system had not been modified during the conversation process; there was no evidence of pre-impact faults in this system.
11.
The propeller blades contained significant rotational energy at the time of the crash; blade angles had been captured at approximately 26 degrees and were consistent with a high engine power setting.
12.
Both engines were under high power at impact; neither engine displayed any pre-impact anomaly or distress that would have prevented normal operation prior to impact.
13.
While the aircraft was in flight, the elevator spring tabs were deflected upward with no corresponding movement of the elevator; this situation occurs when forward control column pressure is applied and the elevator control lock is engaged.
14.
The rudder gust lock's mechanical actuating lever-arm was captured in the ENGAGED position at impact.
15.
A sprocket assembly that interconnects the rudder and elevator control lock actuation mechanisms was oriented midway between the gust lock ENGAGED and gust lock DISENGAGED position.
16.
Damage to the aileron control quadrant's centre pivot-bearing structure is consistent with the aileron control lock being engaged at impact.
17.
Post-accident tests show that, in situations where one or more gust lock pins does not fully disengage, it is possible to have aft (nose-up) elevator authority with no forward (nose-down) elevator control.
Causes
- The gust lock system was not fully disengaged prior to flight and one or more of the gust locking pins became re-engaged for undetermined reasons after lift-off. It is unlikely that a control check had been completed prior to take-off and, once airborne, the crew were unable to disengage the gust lock mechanism before losing control of the aircraft.
In safety action taken, it is stated that:
- Subsequent to this occurrence, the Transportation Safety Board forwarded an Aviation Safety Advisory to Transport Canada concerning the adequacy of pre-take-off checklists and procedures pertaining to the removal of aircraft control gust locks.
A few additional points. The information that the gust lock interaction with throttle levers was changed during modification is false. The throttles could not be moved beyond to approximately 40 per cent of maximum engine power with gust lock handle ENGAGED in the modified aircraft either. The gust lock lever was in a fully DISENGAGED position when recovered, and it was concluded that it would necessarily have been released from its locked position "
prior to, or during, the take-off roll" as otherwise take-off power would not have been available.
Importantly, it was tested that if the elevator gust lock mechanism was left to mid-range position, "
the elevator gust lock pin disengaged sufficiently to allow the elevator to be deflected to command a nose-up pitch attitude. However, because of the system design, when the elevator controls were moved forward to command a nose-down pitch attitude, the control lock would re-engage as the elevator returned to its neutral position."
I hope this gives some kind of conclusion to the case, at least by pointing out what kind of event chain was involved.
-Esa