@jcj:
What you think is not the issue here. I repeat - an AD is only necessary when a fault is severe enough to be likely to cause the loss of the aircraft every time it occurs - for example, the DC-10 cargo door failure leading to hydraulic failure.
If ADs were required in every case where a fault made it possible to lose the aircraft then a lot of the world's fleets would spend a lot of the time grounded.
For example, if you go back to the late 1990s, the 737 fleet was flying around with a known problem in the rudder PCU, they just did not know what that fault was at that stage. The NTSB were considering pushing the FAA and international authorities AD to ground the 737, but it was considered impractical (not to mention the fact that Boeing was fighting tooth-and-nail to get UA535 and US427 classified as pilot error - note that Airbus is *not* doing this in the case of AF447). The NTSB investigator in charge of the 737 issues literally had nightmares about another crash occurring - specifically nightmares in which he was called before Congress and asked why the type was not grounded after two fatal incidents.
Compare that situation - where you have two fatal incidents and an isolated issue, but not enough information to confirm it - with the situation around the Thales pitot tubes, where the issue was successfully solved in 12 incidents out of 13.
Boeing published a workaround which involved maintaining a higher approach speed in the 737 while the issue was being solved. I boarded a few 737s during that period, and I must confess I didn't feel 100% safe, but trusted the pilots enough to get us out of any difficulties.
Likewise, Airbus published a procedure to deal with UAS while the Service Bulletin was taking effect. Unlike with the 737 PCU, the pitot tube fix was known and was being implemented, and with the UAS procedure in place, theoretically things were safe. Unfortunately in the case of AF447 the procedure was not followed.
[NB : The Concorde accident was down to a failure mode which was not considered at the time the aircraft was designed, and no procedure could have saved the aircraft. With AF447, the failure mode was known and workarounds put in place (which, sadly, were not followed) - it's a completely different scenario. ]
Last edited by DozyWannabe; 8th May 2012 at 15:23.