AF 447 Thread no. 4

[RR_NDB]

Redundancy, Fault Tolerance and Graceful Degradation

Lomapaseo

...that has gone wrong in this accident to make this the only so-far upset accident associated with a probable icing failure of the pitot system. Re: Thanks for the incentive, creating more motivation.

Chris Scott

In replying to my post, you have missed the point I was trying to make,...Re: Actually just after reading your post, i was "briefing me" to write what i detected some weeks ago and was not longer concentrated in your arguments. I will think on your key point in respect to the need of graceful degradation.

PJ2,

A very good discussion which resulted from BOAC and Nigel-on-Draft's extended discussion...Re: Thanks for rich information.

mm43,

So why not provide a Normal 2 Law that implements itself in a non latching manner when UAS becomes an issue. This Law would provide a continually updated pseudo KCAS based on all the other environmental data available, including inertial data, and allow the aircraft to maintain stable flight.
Notify the crew and allow them to monitor the situation and ensure that a return to Normal Law occurred when pitot derived airspeeds had stabilized. The object is to remove the "startle factor" and ensure a smooth transition in flight laws to cover what is normally a short period of unreliable airspeed.

Allowing the crew to "monitor" small "crisis", raises the alert level and allows learning from subtle events that are routine (masked by System processing in many cases).

IMHO the crew, specially PF must be capable to immediately understand what´s going on. Obviously to a certain extent. Simultaneous "failure" of critical elements should be reported immediately. The masking (a normal characteristic of a System) of certain faults is not the best approach and can led to delays in implementing proper, precise and in extreme cases, decisive actions.