Saturday, August 06, 2005

Air France Flight 358 - the Likely Cause (2)

Now it seems theories are flooding in on the likely cause for Air France 358's accident at Toronto airport. Until the plane's black boxes can be analysed for the actual data pertaining to the crucial moments of the pilot's loss of control, we may at best speculate.

First there was the suggestion of lightning strike associated with a weather red alert for the airport. While lighting strikes in some rare cases could be fatal or have drastic consequences, in most cases they were not. The real danger in a red alert would be the thunderstorms rather than the potential (not necessarily dead certain) lightning strikes associated with such storms.

The dangers of thunderstorms are the reduced visibility due to heavy rain and low clouds, and the severe and at times violent wind gusts. Reduced visibility means that pilots have to rely on instrument procedures to position the plane for a landing, sometimes known incorrectly as 'blind flying'.

Flying an instrument procedure is never about flying blind. In fact the instrument procedures would have been carefully designed, tested, calibrated, approved and properly documented. Then the pilots would have to be trained, qualified and certificated, or in aviation term be instrument-rated, and as required by aviation rules, practise regularly to retain competency. Both the aircraft and airport radio navigation aids have to be functioning for such an activity to take place.

Modern aircraft such as the Airbus 340 has the most up-to-date instrumentations which together with a modern airport like Toronto having the necessary associated instrument landing radio navigation systems, can even enable automatic instrument landing in the worst possible form of visibility - basically in zero visibility.

It requires consummate skills to either fly the aeroplane manually or operated the automatic instrument landing system which most airline pilots would have trained to - note I mentioned 'most airline pilots' because there would be a few rather dodgy (usually small operators) airlines that may skip such regular training for their pilots after they have been instrument-rated, or may not equip their aeroplanes with the required technology - obviously to save costs.

So, thunderstorms, other than the violent wind gusts, don't threaten that much with poor visibility unless of course the pilots err in their flying or operating of the automatic instrument landing system. Mind you, the gusts can have severe consequences, but in Flight 358 case, the landing seemed to be successful. It was only in its landing run that proved to be disastrous. So we may dismiss the question of gusts, other than the element of an unwanted tailwind which would add to the landing distance.

Then there was my earlier suggestion of asymmetric reversing, which I based on a witness' report. Admittedly I might have leapt to conclusion just a wee too eagerly, based on the wirness' limited observation. Then, I followed that up with the more likely case of aquaplaning, which was touted by several experts. Aquaplaning still remains a big possibility.

There is a new theory now being considered. Could the pilots have landed too far down the runway, and feeling or assessing (pilots prefer the word 'assessing' rather than the rather unprofessional 'feeling') they might have not enough distance to stop, decided to put on engine power in an attempt to take-off again and fly around for a second and hopefully better landing?

Making decisions of this nature can be dicey as a decision left too late is a decision that is bad. A Qantas B747 crashed at Bangkok airport in September 1999 in more or less the same manner, running out of runway in a bad weather landing but fortunately without the breakup and bursting into flames. Some experts pondered whether it could be a case of a late decision to take-off again. As people would say, "Too little, too late."

If an automatic instrument landing had been conducted, then it would be unlikely that the aeroplane had landed too far down the runway, as the approach-to-land would have been governed by electronic signals 'talking' between the runway instrument landing device and the reciprocal aeroplane automatic instrument landing system. If the pilots had flown the aeroplane manually, then human errors could have crept in.

But I reckon aquaplaning is still the most probably culprit.

Related post:
Air France 358 – the Likely Cause!

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