Quote from Conf_iture:
Originally Posted by BEA [see its Habsheim final report of 1990/04/24]
1.16.1.2. Lois de pilotage de l'Airbus A320
Cette loi de pilotage assure en particulier une protection automatique empêchant l'avion d'atteindre une incidence supérieure à 17.5 degrés, pour conserver une marge suffisante par rapport au décrochage, même si le pilote maintient sa demande au plein cabré.
In case it helps anyone, this is my translation into received English:
This flight law provides a special automatic protection preventing the aeroplane from reaching an incidence [angle of attack]
greater than 17.5 degrees, to conserve a sufficient margin with respect to the stall, even if the pilot maintains a full climb [pitch-up]
demand.
Note that this BEA description does not specify that an alpha of 17.5 deg will be achieved if the pilot maintains full back-stick.
An earlier part of 1.16.1.2 sheds light on the question of whether any engagement of
Landing Mode might have at any stage affected the ability of the pilot to achieve Alpha Max. Many of you will prefer to read the original in French, but for those who don't and to save space I'll simply offer this translation:
During all flight-phases prior to the moment the machine reaches a height of 50 feet, measured by the radio altimeter, the flight law is the usual one, called C*.... [there follows a description of the latter]
...
During the phase of descent between 50 and 30 feet, the flight law is modified progressively to take into account (*), instead of the term of load factor [normal G]
, a term in pitch (difference between the pitch recorded passing 50 feet, called the reference pitch, and the instantaneous actual pitch);
when passing 30 feet, a supplementary order intended to simulate an effect of conventional landing is introduced to complement [modify]
the previous pitch law: this order progressively reduces the the reference pitch (established at 50 feet) to -2 degrees in 8 seconds, creating a dive [pitch-down]
moment that the pilot must counteract ("derotation").
At all times, if the angle of attack reaches 14.5 degrees, the flight law is modified and the term of load factor or the term of pitch (whether modified or not by the derotation order) is replaced by a term of incidence [Alpha Prot]
(difference between the current angle of attack and 14.5 degrees). This flight law provides a special automatic protection preventing the aeroplane from reaching an angle of attack greater than 17.5 degrees, to conserve a sufficient margin with respect to the stall, even if the pilot maintains a full climb [pitch-up]
demand.
This latter flight law, by the name of Alpha Prot (angle-of-attack protection), is a priority mode once the angle of attack reaches 14.5 deg. It does not constitute a degraded mode and cannot be de-activated by the crew.
[The section continues with a description of Alpha Floor.]
(*) This transition is progressive: the change of law is effected in one second.
The reference to Alpha Prot being a priority mode suggests that it would take priority over all others, including Landing mode. The report states that the modes/laws of engagement were specifically recorded by the DFDR as follows, where the time base is in seconds relative to the time of "impact", notated as "t" (see also my
previous post). These are listed as follows:
Before [and including?] t - 22, Normal C*;
between t - 21 and t - 20, in transition to landing mode;
between t - 20 and t - 18, progressive return to C*;
between t - 18 and t - 04, landing mode (a reference pitch of +6 deg having been measured passing 50 ft);
at t - 4, switch to Alpha Prot, the angle of attack having exceeded 14.5 degrees; this law maintained thereafter.
Confit and others,
Please let me know soonest of any anomalies in my translations...