Tuesday, June 2, 2009

Air France 447

I've been tracking the tragic loss of Air France flight 447 in the news. As usual, the major news outlets are only reporting a fairly broad overview, while more details are available for those who look. For instance, what about these automated message coming from the airplane before contact was lost. One aviation blog seems to have an inside source about these:
Sources within Air France reported, that the automatic message did not only report an electrical short circuit, but also the loss of cabin pressure. This information has been confirmed by FAB, who also stated, that the position of the airplane was given as N3.5777 W30.3744 in that message.

New information provided by sources within Air France suggests, that the ACARS messages of system failures started to arrive at 02:10Z indicating, that the autopilot had disengaged and the fly by wire system had changed to alternate law. Between 02:11Z and 02:13Z a flurry of messages regarding ADIRU and ISIS faults arrived, at 02:13Z PRIM 1 and SEC 1 faults were indicated, at 02:14Z the last message received was an advisory regarding cabin vertical speed. That sequence of messages could not be independently verified. (source)

ACARS is the data-link that also carries all kinds of useful information between the airplane and the ground. Many news reports seem to be surprised to discover that this exists, though actually it has been around for a long time and is now being phased out in favor of even more advanced communications systems.

Anyway, this series of messages has caused a lot of speculation in online forums devoted to airplane stuff. Many people are pointing to some previous problems with the ADIRU (Air Data Inertial Reference Unit) on the airbus A330 (same type aircraft as this recent crash). In the previous incident, the failure of one of three ADIRU caused the flight computer on Quantas Flight 72 to pitch down violently. 72 passengers were injured, some badly, but the airplane was able to make an emergency landing. There are are three such units onboard so that flight can proceed normally even if two of the three are rendered inoperable. Part of the mystery of flight 72 was why the flight computer didn't recognize and ignore the faulty data.

There other incidents involving "uncommanded" maneuvers as flight computers reacted to faulty data from ADIRU units, so this is naturally the first place people are looking. Yet many other things could have caused this sequence of system failures and messages--a fire being an obvious example (Cf. Swissair 111). We probably won't know the real cause for many months.

Reflecting on this today I thought about how much attention air safety gets compared to, say, car safety. So much more could be done to lessen traffic fatalities. Yet something about the horror of airplane accidents make them much more provocative. I just pray for the families and all who work and travel in the skies....


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