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[Chris Scott]

A319 Wake-Turbulence Encounter

Salut Conf iture,

I think that sensor_validation and you raise a very relevant point about this serious incident or accident in 2008, which was exacerbated by the PF’s over-control in roll and yaw. The TSB of Canada’s report makes very interesting reading. I’m going to repeat the sentence you quoted:

“The automatic reversion to alternate law due to differences in computed angle of attack values was also a product of pilot control inputs.”

Here are some passages from the report’s description of the way the aircraft was handled after the PF disconnected the AP in unexpected wake turbulence, which he apparently mistook for AP misfunction.(Any highlighting is mine.)

Quote:
"During the 18-second duration of the event, heading varied from 065ºM to 086ºM. The captain reacted to the rolls with a total of nine sidestick roll inputs, accompanied by coordinated rudder pedal deflections. Five sidestick inputs were to full travel of 20º."

Quote:
"From 06:48:07 to 06:48:25, pilot sidestick roll inputs were 90º out of phase with aircraft motion. From 06:48:07 to 06:48:15, lateral accelerations and heading deviations were approximately 90º out of phase with the rudder pedals. This indicated that after the autopilot was disconnected, most of the aircraft motion in the roll axis resulted from pilot inputs and that lateral accelerations were due mostly to pilot rudder control inputs."

Quote:
“Abnormal accelerations in the normal or vertical axis were correlated with changes in angle of attack, and sidestick pitch control inputs opposed these aircraft angle of attack excursions.”

I think the expression “sidestick pitch control inputs” may have been unintended, because it goes on to say:
“...the accelerations in the vertical were a result of external influences on angle of attack associated with wake turbulence,”
　
In March 2008 – long before the issue of the TSB of Canada’s report – PPRuNe (as CONF iture, PJ2 and others will remember) was discussing at length a rough landing by an A320 in a limiting crosswind at Hamburg. The subject of SIDESTICK technique came up when someone gave a link to this

video" target="_blank">video

of a pilot using the sidestick during a crosswind landing. (N.B. This was NOT a video of the Hamburg incident!) One poster described it as coffee stirring. Having seen it before from the jump seat during 12 years’ line-checking, I called it “sidestick abuse” in this post:
http://www.pprune.org/tech-log/31609...ml#post3979423

[SIZE=2][FONT=Verdana]As for the use of "co-ordinated" RUDDER at cruise speeds, I would argue that it was nothing of the kind: the report suggests that, notwithstanding the rudder-travel limiter, A320-family pedal loads need to be increased. (No comment re the A330.) Should rudder ever be used in cruise-flight, apart from the asymmetry case? I remember being disturbed by one copilot, who moved a pedal significantly when stretching a leg that had "gone to sleep".

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.