Originally Posted by GerardC, Post #3020
Well... not really. According to AF book (see BEA's report appendix 9), when ALL IAS are unreliable "sécurité du vol" must be considered "affectée" and 5° NU/TOGA drill MUST be performed.
I don't read or speak French. If I may, could I ask that the paragraph beginning with the statement, "
Si la sécurité du vol est affectée", be translated? I would like to understand exactly what it is saying. Specifically, I would like to know where it says, "
and 5° NU/TOGA drill MUST be performed." Thanks very much.
In the UAS drill's design, the memorized items are for when the crew doesn't have time to look up the pitch and power, and instead must react very quickly, for example on takeoff. Remember, this drill has evolved from the original ones written a few years after the Birgenair and Aeroperu accidents.
When in stable cruise flight at FL350, a loss of any or all airspeed indications is not an emergency like the loss of engine thrust, loss of cabin pressure or a fire warning. One is not required to instantly act and "do something".
I think a mandatory pitch of 5degrees at cruise altitude if the airspeed is suddenly unreliable is a serious error in checklist design and the wrong guidance to the response given what would result if one pitched the aircraft from 2.5deg to 5deg.
The result would be destabilizing because level flight has been lost in the resulting climb and there is no longer any pitch and power reference with which to stabilize the speed because 5deg NU is going to cause a loss of energy/speed and if one is pitched up, one has no idea what one's speed is regardless of the power setting. At cruise altitude, there isn't much reserve power and pitch attitudes for most climbs when changing altitudes are usually a half to one degree higher than cruise pitch. A 2.5degree increase in pitch is huge.
Further, if the memorized drill requires "5deg" when the aircraft is clearly above both the MSA and circuit altitude" (the last memorized item in the box), then the drill is open-ended and does not provide for a level-off point from which to troubleshoot. It might be argued that at some point a crew flying this airplane, knowing that it is losing speed and energy, (one would hope they knew!), would level off because the result of a continued pitch-up is obvious. Of course, that then begs the question of the mandatory pitch-up in the first place, does it not, so why would anyone ever do it?
I think that if a mandatory pitch-up to 5deg whenever the aircraft is above FL100 which may have been the last training on this abnormal that the PF had received, then perhaps we have the reason why the PF pitched up almost instantly, and unannounced to the PNF, upon the loss of the speed indication. But I can't for the life of me really believe that that is what the drill means or requires, is it?
Pitching the aircraft up like that rather than maintaining level, stable flight is a guaranteed loss of situational awareness and potential loss of control as happened here, whereas maintaining level flight with pitch and power settings "as they were", keeps all factors in the "known" territory while the speeds sort themselves out.
I don't understand why two things aren't abundantly clear to everyone upon pitching up to 5deg - a) what the airplane would immediately do, and b) regardless of the memorized items which would mostly be applied during takeoff or early in the climb, why is there any support at all for a pitch-up to 5deg at cruise altitudes, when the outcome of such a manoeuvre is quite clear?
The question might be rephrased thus: Do we follow a bad checklist and place the flight at serious risk or are we pilots who think and fly to stay alive?
It isn't complicated and it certainly wasn't an emergency requiring the instant action that occurred.