Monday, 15 March 2010

Lives and Cost/benefit analysis

Bristol lost three schoolkids last year in crashes. The anniversaries of the deaths of two will be next month, deaths that should not have happened.

The one we haven't covered yet was an 11 year old, Alexander Bjoroy, flying to Clifton College from Brazil. Here's the school with a US flag at half mast. Why the US flag? At half mast? The Omaha Beach landings of D-Day were planned here by the US army. Decisions were made there that impacted the lives of people all round the world. After the war, the US army presented their flag -this one is apparently a replacement which formerly flew above the US Congress.

US flag over Clifton College

In 2009, Alexander Bjoroy died because of other decisions made. Der Spiegel has put up a fairly bleak an analysis of what happened on AF-447.
  1. With the passenger and freight loads of the flight from Rio to Paris, the only way the Airbus 330  had the fuel capacity for flight + minimum emergency fuel was by pretending the destination was Bordeaux, and then, if when they get close to there and they "happen" to have enough fuel, continuing to Paris. Yet the landing costs and delays aren't included in the schedule, so it's not something the pilots are actually encouraged to do.
  2. There was a storm, and without the surplus fuel, the pilots chose to fly through it, rather than round.
  3. All three pitot tubes, which measure airspeed, froze. The online computer didn't know what to do.
  4. The airplane stalled and fell out the sky. Attempts to restart the flight computer were recorded by messages sent from the airplane's computer to Air France, but they clearly had no effect.
  5. The plane crashed into the sea with a force of 36G; so hard the tailfin sheared off. The oxygen marks didn't deploy, nobody had life jackets out and the stewardesses weren't in their emergency seats.
  6. Everybody died. 
The coverate of the airspeed sensors, the pitot tubes is poignant. 
  • Military airplanes heat their pitot tubes to prevent freezing
  • The civilian FAA test requirements predate jet planes and only test for temperatures expected at or below 9km, yet this plane (and all other planes for which pitot tube freezes have been recorde) was at 10km.
  • Air France has opted not to spend the €300K per plane needed to add some software that Airbus sells to help pilots angle the plane correctly after airspeed indicator failure.
Given the size of the AF fleet,  €300K per plane probably adds up. But for anyone who lost a friend or relative on the flight, the money would have been justifed. Some questions may need to be asked of Airbus itself, however, and this brings us back to Bristol, where parts of the planes come from. If the pitot tubes are known to fail, and are used at heights/temperatures outside their test space, why doesn't Airbus provide this software for free. Surely it exists to correct a design defect in the plane itself?

[some coverage in the software engineering community. The A320 was the first civilian fly-by-wire plane, and there's still debate about whether it was a wise decision for it, its successors, and recent Boeing planes.

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