Clandestino
Two of you are referring to low G stall, which is gentle due to low speed! AF447 a) never achieved that b) did suffer from pretty heavy pre-stall buffet. I see no point in further developing this line of discussion, except some entertainment.
BEA FR 2.3.3 Stall warning (operation and identification)
Furthermore, in alternate or direct laws as featured in the manufacturer’s manual (FCOM), the stall warning is described as being the combination of the aural warning, the illumination of the Master Warning light on the FCU and the indication on the speed tape, displayed as a red and black strip (Vsw). No clear mention of the buffet phenomenon is ever made.
safetypee
Clandestino, your conclusion “Both pilots commented that speed display was faulty” (#819) assumes a particular interpretation. The absence of airspeed does not imply URA as depicted by the abnormal drill. Also, if the speed display had disappeared off-scale low this may have reinforced the idea of a stall because of the decreasing speed.
BEA FR 3.1 Findings
The crew, progressively becoming de-structured, likely never understood that it was faced with a “simple” loss of three sources of airspeed information.
safetypee
Re “Stall...recovery...in...normal...law...was...never...traine d”.
You may have overlooked the nuance of my hypothesis, in that because stall ‘wasn’t possible’ in normal law there was a mental conflict with a stall warning and low speed / decreasing speed, before any appreciation (if at all) that the aircraft was in Alt Law. The erroneous mental model might also have been reinforced by the concern over turbulence from adjacent Cbs.
Thus whether trained or not, the PF chose a course of action closest to the perceived situation based on previous experiences / bias. This was to fly a stall recovery based on a false mental model, and with both supportive and conflicting indications of that model.
BEA FR 3.1 Findings
The aeroplane went into a sustained stall, signalled by the stall warning and strong buffet. Despite these persistent symptoms, the crew never understood that they were stalling and consequently never applied a recovery manoeuvre. The combination of the ergonomics of the warning design, the conditions in which airline pilots are trained and exposed to stalls during their professional training and the process of recurrent training does not generate the expected behaviour in any acceptable reliable way.
In its current form, recognizing the stall warning, even associated with buffet, supposes that the crew accords a minimum level of “legitimacy” to it. This then supposes sufficient previous experience of stalls, a minimum of cognitive availability and understanding of the situation, knowledge of the aeroplane (and its protection modes) and its flight physics. An examination of the current training for airline pilots does not, in general, provide convincing indications of the building and maintenance of the associated skills
I hope that helps in the discussion.