THE CURRENT CASE in Norway concerning the 1990 crash of a Wideroe Flyveselskap DHC-6 Twin Otter is the latest in a long line of challenges to accident reports. In this case, as in the others, the controversy stems more from the procedures for making a challenge than from the scientific basis of the challenge itself. That this aircraft crashed is not in question; that it crashed because of a loss of control following a failure in the tail of the aircraft is equally not in question. On the surface, the dispute is over which failure precipitated that loss of control. In reality, it is over who has the final say when an accident finding is challenged.
The official report and a subsequent review of that report, pinpoint an aerodynamically induced structural failure in the tailplane itself. Independent experts claim that the tailplane only failed when the aircraft hit the water, and that the initial cause of failure was the fatigue failure of an elevator control rod.
If the findings of the official report are correct, the aircraft crashed because a crucial part had been stressed beyond the design limits in bad weather. That would have few implications for the aviation community beyond the need to remind pilots of the inadvisability of knowingly flying into extreme weather.
If, however, the independent investigators were shown to be right, the implications would be far greater. If a part fails because of fatigue within its fatigue life, either the part was wrongly designed for its intended service, or the service conditions to which it has been subjected are more severe than it was designed for. Either way, the design and/or operation of the aircraft could be called into question. So could the ability or integrity of the original investigation team, and that of the team from a separate institution, which reviewed their findings.
Air-accident investigation is, by and large, a painstakingly thorough science: short-cuts are rarely taken; theories are rarely discarded without cause; decisions are rarely compromised. Investigation findings are rarely challenged, because the aviation community has a great deal of faith and trust in investigators.
That frees accident investigators from the constant review and challenge, which bedevils most legal systems - but it also means that the investigation system does not have the same formalised appeal and review mechanisms. In most countries, an investigation can be challenged via some form of judicial review. In very few countries is that a simple or quick exercise, and in some countries such as the UK it has been made positively harder in recent times. By its very nature, that form of review is more likely to be legalistic than scientific.
The investigative equivalent of a legal re-trial, in which a new team of investigators might start from scratch armed with all the original evidence plus any new evidence which has subsequently come to light, is almost unheard-of. The review of the Norwegian case appears to have followed this pattern: an independent review body has reviewed the findings of the original investigation.
Its findings must inevitably concentrate more on the interpretation of evidence than on the quality of that evidence. If a potentially material fact was discarded as being incidental at the start of the process, such a review may be able to do little to rectify the situation. The wrong questions, in effect, may be being asked of or by the review body.
Obviously, the last thing the air-accident process needs is a lot of second-guessing, no matter how well informed that second-guessing may be. However, there are occasions when a fundamental review may be justified. The question then becomes - who is qualified to do that review?
The only possible answer can be that it must be a non-partisan body of investigating excellence - and that means a review body drawn from the best of the existing, practising investigators. To conduct reviews in such a way would be expensive, inconvenient and time-consuming, and would require a formalised universal international agreement - but to review such serious matters in any other way seems almost irresponsible.
Source: Flight International
