AF 447 Thread No. 11

[Chris Scott]

Hi Winnerhofer,

Thanks for your link to the "full" Transcription CVR from the Rapport d'Expertise of 2012 (sometimes referred to as the judicial report), and the Conclusions.

It fills in some of the "(...)"s in the transcript pubished in Appendix 1 of the BEA Final Report, and there are some split-second variations in timing. However, I've yet to find any evidence of supernumerary presence in the cockpit, which you claimed a few days ago?

Re your latest post, quote:
e) As a system, the A330 is not tolerant to single failure of the Pitot probes, which is contrary to all the rules of reliability and dependability . For an event of this severity (catastrophic , in the sense of the term dependability , i.e. which can cause victims), the system must be fail-safe design (it must guarantee the safety of the flight despite the failure ), and even FS / FS that is tolerant to double down.

I've never been involved in engineering or standards of certification, but venture to suggest that, as a system, the A330 and its crew is indeed tolerant to a failure of all 3 airspeed probes, provided the crew acts in a manner that might be expected of one which is properly qualified in terms of training and experience. Having said that, it is clear that the training, SOPs and the UAS drills/checklist left much to be desired.

Quote:
Namely redundancy probes (actually 3 ) is false redundancy since all the sensors are the same technology therefore likely to fail at the same time , under the effect of a single common cause .. . icing.

Yes, and this is not peculiar to Airbus, When we discussed this a couple of years ago on an AF447 thread, I commented that it had sometimes crossed my mind - during external checks on various a/c, incuding Airbuses - that the policy of mounting pitot probes and AoA probes symmetrically left and right invites the coincidence in timing of any icing problems. This tends to pertain to the #1 & #2 probes, with the #3 being asymmetric to them. One can understand the traditional philosophy of similarity of the two primary detectors, but it will be interesting to see if AF447 leads to a rethink at least in terms of the siting of probes, if not dissimilar specifications of the probes (and/or probe-heaters) themselves.