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Friday, 31 December 2010

Flight 447: The conclusion

In my post last year regarding the crash of Flight 447, I asked five burning questions. But I only answered four:
I'll answer Question Number Five now, as Question Number Four will take a while.
It's taken a while all right, but I'm now ready to answer Question Four, "Could it have been caused by bad weather?"

I actually brought up the issue in my opening post:
. . . or perhaps had actually flown into the ocean in bad weather.

None of these things happen now.
No, as it appears, this is precisely what did happen--but it shouldn't have. Let me break the incident down into a chain of events, and we can perhaps see why, despite all the advances in technology that the Air France Airbus A330 represented, engineers had not yet succeeded in designing out the Human Factor that inevitably plays a part in every flight incident. Or, to put it another way, they had succeeded a bit too well-and still, yet not enough.

1. The Airbus 330 was designed with a computer-controlled flight system, that will only hand control back to the pilot in case of an extreme emergency. A crucial aspect of this system is that the fuel setting is adjusted directly by the computer, without any input from the hand throttle. This is unlike the cruise control of an automobile or even the computer controls of other aircraft, in which the throttle can be seen or felt to physically move as speed is adjusted.

2. Pilots being trained to fly the Airbus were never trained on the scenario of computer flight control failure due to loss of speed input. In such a case, standard operating procedure would call for controlling air speed by pitch and power alone.

3. In the weeks leading up to June 1, 2009, several incidents were reported of 300-series Airbus aircraft losing speed input due to Pitot Tube blockage. Airbus ordered modifications, and as of June 1, Air France had not yet finished implementing them on its Airbus fleet--particularly not on the plane flown on Flight 447. This was an Equipment Failure waiting to happen.

4. At 5700 miles, the Rio de Janieiro to Paris route was the longest nonstop distance regularly flown by a twin-engine aircraft--and most of it was over the Atlantic. Flight rules prohibiting a plane from flying on its fuel reserves meant that going around the 250-mile wide Intertropical Front that had developed on June 1, 2009 could burn up enough fuel to require the pilot to land and refuel short of his destination--adding time and expense to the trip when he actually had enough fuel on board to make it. Knowing this would put pressure on a pilot to seek a way through, rather than around, the Front. Thus the Economic Factor enters the picture.

5. As Flight 447 approached the Front, a small storm between the plane and the Front could have blocked the pilot's weather radar from picking up the huge storm behind it. Changing the sensitivity setting on the radar could have overcome the problem, but it doesn't appear that this was done. The First Thing had gone wrong, and there was a Human Factor compounding it.

6. As Flight 447 entered the thunderstorm, it encountered turbulence. Standard procedure in such a situation is to cut power to slow the aircraft. At 35,000 feet, the air is so thin that only a slight power reduction is safe. Too much, and the wings will lose lift. Since the computer was flying the plane, the pilot dialed in a lower power setting; the hand throttle remained in its previous position. So far so good, but the Design Factor has now entered the picture, and it will take only a small Human Error to cause further complications. As it turns out, Airbus Pilots will be shown to have been generally inattentive to speed settings during flight incidents involving Pitot Tube failure. The Oversight Factor had just added to the complications, and the Flight Incident hadn't even quite begun.

7. The Air France pilots must have been aware that they were entering a major thunderstorm, but at over 500 miles an hour, they were entering it, controlled by the flight computer, at a rate of a mile every seven seconds. Downdrafts of up to 100 feet per second, coupled with instant icing by supercooled water, meant that at the very instant the Pitot Tubes froze over and loss of airspeed indication shut down the autopilot, the pilots would have had to scramble to gain control the aircraft. Flight 447 was now experiencing a Flight Incident caused by Severe Weather, and the Training Factor had just kicked in. Everything would go downhill from there.

8. The pilots then attempted to control the plane by pitch and power, but apparently forgot that the computer had already slowed the plane. The static tube had probably also frozen over at this point, leaving them with no altitude indicator short of ground-proximity radar. Training deficiencies, Design deficiencies, and inadequate Oversight now combined to take the aircraft into a stall--a maneuver in which a plane can lose half its altitude in just a few seconds. Pilots don't ever get to actually practice stalls on their expensive airplanes, especially not at night with no horizon visible. If the pilot was able to pull out of the stall in time, he apparently over-corrected, pulling the plane up into another stall, but this time too close to the surface to have room to recover. As the plane pulled out of this second stall, it ran out of airspace and hit the surface of the Atlantic. Indeed, Air France Flight 447 flew into the ocean in bad weather.

It all comes down to the human factor. An ex-fighter pilot, used to stick-and-rudder flying at a wide range of speeds and attitudes, probably could have flown the aircraft through the storm and safely out the other side, regardless of equipment failures. But a pair of air transport pilots, used to letting the computer fly the plane from just after takeoff to just before landing, weren't up to the job. When the Pitot Tubes failed, causing the flight control computers to fail, they were the last point of defense for Flight 447's 228 passengers and crew. And when they failed, everybody died.

I'm getting a lot of hits to this page, presumably from people looking for background information on the fate of Malaysian Airlines Flight  370. This is an even more curious case, as the Boeing 777 appears to have fallen out of a clear blue sky. My taken on the question is that it was blown up; I can't think of any other explanation. Whether it was by a missile, or an on-board explosion, time will tell; the information being released now isn't enough to go on.
There is yet one other possibility, far more chilling: that nothing will be found of Flight 370. It is explored here.
For my post of Flight 370, see here. It was apparently flown into the sea at stall speed, allowing it to sink slowly to the bottom in such a way that the wreckage will not be found for years.

1 comment:

  1. yes u r right t.....thnks for your report


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