PF Transition from AP with Normal Law to AP-OFF with ALTN 2 Law
I wrote (currently post #3556), in the light of the TSB of Canada’s report[FONT=Verdana][SIZE=2]
of an A319 wake-turbulence encounter:
"In view of the possibility that AF447 encountered sudden, severe turbulence, perhaps we should be adding another scenario to the list of possible causes of LOC and Control-Law degradation. Could it be compatible with the analysis of ACARS messages? I think it might be."
Was the original fault that led to the degradation from Normal Law to Alternate-2 (ALTN2) Law either:
(a) AoA-probe anomalies caused by pilot-induced yaw;
or
(b) pitot-probe anomalies caused (perhaps) by icing?
CONF iture points out:
"...the message related to the pitot tubes which, in my opinion, is absolutely central in the AF447 ending."
So (a) looks less likely than (b).
However, CONF iture continues:
"We know how easy it is to over control especially with the sidestick.
The indicated airspeed may be little, but the real true airspeed would not cope well with anything more than tiny sidestick solicitations ..."
During the minute from 0210z, for whatever reason, the PF undoubtedly found himself in Alternate Law (probably ALTN 2), sans-AP, trying to keep the wings level (or fly a safe turn) and control the pitch. ALTN 2 does not apply in the case of the A320 family, but the DFDR trace (reproduced above by Machinbird) shows an experienced PF trying to cope with the transition from AP to sidestick and Alternate Law in moderate-severe turbulence on an A319.
Again in the light of the TSB of Canada’s report, I also wrote:
Should rudder ever be used in cruise-flight, apart from the asymmetry case?
If the answer to that is in the negative, there is now more than anecdotal evidence that some pilots do use rudder at any speed, and that undesired yaw-cycling can be the result. This may compromise aerodynamics and/or structure; and even the quality of sensor-data in the ADRs.
Last edited by Jetdriver; 18th April 2011 at 15:59.