The Germanwings A320 crash
At this stage there’s not more that can be said about the particulars of this tragedy that has claimed a 150 lives in a mountainous corner of France. Disturbingly again we have an A320 aircraft descending rapidly and apparently out of control, without the crew having any time to issue a distress call. Yet more disturbing is the though that the crash might be due to the crew failing to carry out the workaround for two blocked AoA probes promulgated in this Emergency Airworthiness Directive (EAD) that was issued in December of last year. And, as the final and rather unpleasant icing on this particular cake, there is the followup question as to whether the problem covered by the directive might also have been a causal factor in the AirAsia flight 8501 crash. That, if it be the case, would be very, very nasty indeed.
Unfortunately at this stage the answer to all of the above questions is that no one knows the answer, especially as the Indonesian investigators have declined to issue any further information on the causes of the Air Asia crash. However what we can be sure of is that given the highly dependable nature of aircraft systems the answer when it comes will comprise an apparently unlikely combinations of events, actions and circumstance, because that is the nature of accidents that occur in high dependability systems. One thing that’s also for sure, there’ll be little sleep in Toulouse until the FDRs are recovered, and maybe not much after that….
if having read the EAD your’e left wondering why it directed that two ADR’s be turned off it’s simply that by doing so you push the aircraft out of what’s called Normal law, where Alpha protection is trying to drive the nose down, into Alternate law, where the (erroneous) Alpha protection is removed. Of course in order to do so you need to be able to recognise, diagnose and apply the correct action, which also generally requires training.