Hi gums;
Re, "
THNX, Retired for discussing how easy using an AoA indication is.
Sucker shows stall or optimum approach speed or.... regardless of your weight. And we can still use rules-of-thumb to make a comparison - you know, 175 knots plus 5 knots for every thousand pounds above 3,000 ( F-101B VooDoo). If the AoA is really high or low at the textbook speed, check your flaps or fuel gauge or... And that's the OODA I was referring to, PJ, basic instrument crosscheck. "
Thanks - I learned something again...OODA. We have a slightly different approach but I believe the outcome is the same. Thanks for bringing it up.
I have a question regarding an AoA indicator and how airline crews would use it.
With reference to the following, from the BEA Interim Report #2, pg46, it states:
In alternate or direct law, the angle-of-attack protections are no longer available but a stall warning is triggered when the greatest of the valid angle-of-attack values exceeds a certain threshold. In clean confi guration, this threshold depends, in particular, on the Mach value in such a way that it decreases when the Mach increases. It is the highest of the valid Mach values that is used to determine the threshold. If none of the three Mach values is valid, a Mach value close to zero is used. For example, it is of the order of 10° at Mach 0.3 and of 4° at Mach 0.8.
My question is, how does one use the guage in operations, and how does one stay away from the stall AoA using an AoA guage when the AoA at which the aircraft will stall changes with Mach? Would the guage be calibrated, (
using much the same logic as the ECAM does in Alt/Dir Law - a table was posted around Thread 4 or 5 showing this AoA calculation at which the stall warning would sound).
I'm not arguing against installing/using an AoA guage here. I frequently interrogated the ACARS function to watch the flight data which included the AoA among many other interesting parameters.
But, if I may, I think that there is more to an AoA guage than just installing and selectively watching it. Clearly, the AoA at which a transport will stall at high Mach number at cruise altitude is different (due Mach effect) than an approach AoA which is typically 8 to 12deg depending. In cruise, a stall AoA may be as low as 4deg, as it was here when the first blip of the stall warning was heard, and later, at a much-reduced Mach but at FL376 or so, the aircraft was starting to stall at an AoA of around 7deg. I'm trying here to imagine how the guage would get the crew/PF of AF447 out of trouble and how the PF would use an AoA indication and what AoA he would be targeting.