Contemporary FCOM extracts
Quote from rudderrudderrat:
"From my FCOM:
• αfloor is activated through the A/THR system, when
α is greater than αfloor (9.5 ° in configuration 0; 15 ° in configuration 1, 2; 14 ° in configuration 3; 13 ° in configuration FULL)"
I guess that must be a FCOM from a later era than June 1988? Here is the equivalent paragraph from the BCAL Tech Manual, dated 17FEB1988, around the time of A320-100 type-certification. [I'm stuck with transcribing it in plain script.]
Alpha-floor is activated when:
- alpha > alpha-floor (9.5 deg in conf 0; 15 deg in conf 1, 2, 3; 14.5 deg in conf FULL, or
- sidestick deflection > 14 deg nose-up and pitch-attitude > 25 deg or in angle-of-attack protection [sic...].
[The ambiguous mix of "and" and "or" in the final, un-punctuated sentence is as printed.]
A slightly earlier, late-1987 edition of the Airbus FCOM Flight Controls chapter (1.09.10 P8, REV 03, SEQ 001) omits any specific alpha figures; instead providing the following figures of the relationship between the alphas at the protection stages and the alpha at Vs.
All configurations at low speed:
alpha-prot >= alpha (1.13 Vs)
alpha-floor = alpha (1.1 Vs)
alpha-max = alpha (1.06 Vs)
Clean configuration at high speed:
alpha-prot = alpha (buffet)
alpha-max = Czmax
When alpha protection is active nose-up auto-pitch-trim is inhibited.
One might assume in the above that Vs is a speed associated with the alpha at CL -max, but it does not state whether that Vs is at 1.0G or a lower figure. And whether it is the same value used in the "Stalling Speeds" graph (FCOM 3.01.20 P5) is unclear.
Therefore, I think any attempt, using a combination of the above sources, to infer specific values of alpha for the three different protection levels might be ill-founded. Also, the two versions may originate either side of the FBW certification process.
Hi Jesse,
"A FLOOR doesn't work below 100'RA."
Yes, we have discussed that previously, although my 1988 manuals only seemed to mention it in the Power Plant section (A/THR automatic-engagement criteria). The Habsheim crew had planned to disable Alpha-Floor to ensure it did not intervene at their briefed display height of 100ft.