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Old 26th Feb 2014, 23:46
  #558 (permalink)  
DozyWannabe
 
Join Date: Jul 2002
Location: UK
Posts: 3,182
Originally Posted by roulishollandais View Post
@Others:
I wonder why Asseline want to fly his Airbus at "alphamax" and uses that word in his briefing?
Because that was the point of that part of the sortie as briefed.

Why doesn't he mention Alpha Prot? Both pilots seem to have approximative knowing of their plane?
Alpha Max is the maximum achievable AoA when in High AoA Protection mode, whereas Alpha Prot (the value) is the AoA it will achieve without additional back-stick. It follows that if his intent was to achieve Alpha Max, then Alpha Prot would not require coverage in the briefing.

What can be confusing to people who are not as obsessive over the technical details as many of us is that some parties, when referring to the *mode* that Airbus name in their own documentation as "High AoA Protection", abbreviate that name as "Alpha Protection".

The "High AoA Protection" mode and "Alpha Prot" value are two very distinct things, and should not be confused.

It should be noted that Airbus themselves do not, to the best of my knowledge, use that particular abbreviation in their technical documentation.

Why is the value of Alpha Prot from the BEA final report for Alpha Prot incidence 14.5 and differs from Asseline's book shematic p.420 where Alpha Prot is 12 ?
Honestly, I don't know - it would depend on the sources Asseline is using, particularly with regard to the publishing dates.

I'm also unsure as to what point Asseline is trying to make, as the AoA of the aircraft during the phase where the protection logic commanded nose-down elevator was a little over 15 degrees, which is in excess of both stated values.

From the same book, page 432, why does Bernard Ziegler requests to R.DEQUE, G.PICHON, B.BISSEY, P.BAUD an improvment of Alpha Floor to alpha 12 (14 feb 1990, two months after Bengalore) and the Habsheim final report is giving Alpha Floor =15 ?
Presumably because that request (which - if accepted - would have reduced the Alpha Floor AoA trigger by some three degrees) was made over a year after Habsheim. Alpha Floor behaviour is somewhat moot in any case, because A/THR (and thus Alpha Floor) was supposed to have been disabled in order to maintain Alpha Max at a steady altitude - and in the event was inhibited by allowing the aircraft to descend below 100ft RA.

How many degrees incidence are given in books today to A320 pilots and correspondant speed for steady level flight, in the conditions of Habsheim flight and MLW for :
If you look at the graphs posted earlier in the thread, degrees incidence (at least of the Alpha values) are neither specified nor annotated in Airbus's recent pilot documentation, and I'd guess that they weren't then either.

The graphs can therefore convey only a qualitative idea of how the High AoA Protection responds, and this makes sense for at least two reasons I can think of off the top of my head.

Firstly, production A320s are not fitted with an AoA gauge - and so to annotate the graph with precise values would be of little use to flight crews.

Secondly, and as the general direction of the thread has indicated, the values themselves represent only what can *possibly* be achieved - i.e. in optimum conditions. In the case of Habsheim, the aircraft was low, slow - and with the engines spooled down until far too late it was continuing to decelerate until possibly a second or so prior to impact. These are pretty much the polar opposite of optimum conditions, and in such events the systems will comply as best they can with what they have to work with.

There's also (IMO less important) the aspect that the precise trigger values may change due to operational experience and feedback from the line, as the A. Floor request you mentioned hints at, but the overall behaviour pattern will not. No need to republish the FCOM if the values aren't specified.

Last edited by DozyWannabe; 27th Feb 2014 at 00:16.
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