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Jun 9, 2009

AF447: what we know so far

If a reasonable guess is to made about what was happening on AF447 that night, it was that the jet was flying at perhaps the worst possible speed into a storm cell. Ben Sandilands explains.

Ben Sandilands — Editor of Plane Talking

Ben Sandilands

Editor of Plane Talking

While nothing will stop the torrent of speculation about the causes of the Air France crash in the mid-Atlantic on 1 June, the recovery of a large section of the tail removes some theories.

The rudder, which is a moveable control surface, didn’t break off the vertical stabiliser or “fin”.

They broke off together where they were bolted on to the top of the rear fuselage, exactly where they should break first if subjected to great violence.

No-one knows yet if that violence occurred in the air, where the jet may have been subjected to fierce bending and twisting forces, or when the plunging wreck tore into the surface of the sea.

But there is now a progression of events confirmed by the statements made by the accident investigator and the airline, a sequence of what is known to have occurred in the final minutes of AF447, the flight that killed all 228 people who were on their way to Paris from Rio de Janeiro.

Less than half an hour after the pilots talked to the operations centre in Paris, mentioning strong turbulence, a series of automated service messages relayed by satellite indicate a rapidly mounting series of problems.

They begin with the autopilot disconnecting because of problems with the systems that provide it with essential data, including air speed.

They extend through the control architecture of the jet, with an early report of the rudder travel limiter, a function that restricts rudder deflection at higher speeds, no longer being available as an automatic protection against inputs that could put a flight at risk.

Almost every Airbus or Boeing anyone is likely to fly on has a system for restricting rudder deflections with rising speeds.

We also know the pilots no longer had reliable consistent indications of their airspeed. Air France attributes this to faults in the external pitots used to inform the flight control computers and pilots how fast the jet is going.

Air France was so concerned about these pitot failures (which are not the same as those in Qantas A330s) that it began replacing them in April, with work due to have been completed on all of its A330s by the end of this month.

If a reasonable guess is to made about what was happening on AF447 that night, it was that the jet was flying at perhaps the worst possible speed into what may have been one of the worst possible places to go, a storm cell, and everyone on board paid the worst possible penalty.

We do not know if the jet experienced a high speed stall before it crashed, or was retarded into a stall or otherwise crippled by running into severe updrafts and downdraughts in a storm cell.

But we do know that if you fly a jet airliner into the “wrong” violent storm it can be destroyed in mid air or rendered uncontrollable. Hitting a severe storm cell is like hitting something almost as solid as a dense sheet of water. The jet decelerates so rapidly, the load limits on critical parts of its structure are taken beyond breaking point.

The chances of finding the two “black boxes” recording flight data and the cockpit conversations have been enhanced by the recovery of the fin, as they are mounted in the back of the fuselage near the vertical stabiliser.

Working backwards from best guesses of wreckage drift caused by currents and winds, the submersible recovery vessels due in the area later this week will have a much smaller area in which to listen for signals and locate and recover the devices.

The AF447 accident has spawned an incredible amount of garbage in some newspaper, even the Sunday Times, and on websites about “scarebuses” and the “dangers of computers” and so forth.

Reality check. There are at any one time current safety issues with most types of airliners arising from in flight errors or other experiences. Dozens of them are dealt with every year. And there are issues with the way some airlines fly their Airbuses and Boeings, without prejudicing Air France, which unlike some carriers, invests heavily in flight standards.

At least 24 bodies have now been recovered from the crash zone.

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2 thoughts on “AF447: what we know so far

  1. John Bennetts

    Thanks for wrapping up that which is currently known about this accident and addressing the worst of the scare stories in this short, precise article.

    Not a wasted word.

    I hope that all of the grieving can come to terms with the facts and not become trapped in an emotional search for some one to blame.

  2. Bonnie Ember

    Hello Ben,

    Great, Objective articles.
    I have read everything from Aliens to Meteors, hit AF 447.

    We do know that the Pilot from Iberia saw a flash of white light that broke into 6 pieces & fell vertically to earth, about the same time as the AF flight, & about in, the same flight path.
    We do know that, Whatever happened to that plane during those 4 minutes of Computer generated error messages, The Pilots could not send a May Day call.

    It reminds me of the film: Westworld, where the computers take over, & murder the people.

    Although this is Life, imitating Art,
    There are so many Hackers out there, that I do not like the idea of a plane flown by computers.
    We need a better system for measuring air speed on a plane.

    I just got back from the ITCV filming an HD film on Tahiti which can be seen on: