Graybeard
"Maybe the TCAS Fail was like the Wiring Fail reported: the plane could have been getting the crap shaken out of it."
The autopilot dropped due to A) unreliable airspeed, B) exceeded control limits.
The a/p needn't be commanded to drop by the FMS (AD disagree). It will drop involuntarily all by itself if it cannot control the airplane, (within its limits). If it drops for this reason, Normal Law is retained with Stall protections and overbank protections. If for whatever reason the pitots inhale 30 knot disacrepant airflow, there we have AD disagree, though not ice caused, but turbulence caused. Now it drops to Alternate Law, but ostensibly for other than Unreliable Airspeed. If turbulence induced, one could argue it is not truly unreliable, but for 30 seconds some form of local upset in airflow has discreped the pitot tubes (perhaps both on the same side).
Any turbulence of this description can be sudden in onset. An updraft of 100 knots could be proposed, (Let's give it a radial component just to be mean). An argument could ensue whether its borders would be crisp enough to differentiate long enough between fuselage halves to cause UAS. Either way, there is an in and out (out and back in?) Law exchange that may have occurred. Musical protections? goddamitey, what a handful. (The radial component, from the left, would give it a left wing high result).
An updraft would give it a boost in lift, and a diminution of IAS. Enough of a drop in IAS to cause "UAS"?
IF AoA is AS and Vane reliant, a temporary boost in indicated AoA, reduction of IAS, and rising VS, does this fool the FCS? Was 447 in a transient and turbulence induced Phantom Upset? Something a hand flying pilot may have patiently sat through?
Autoflight into severe Turbulence? VIABLE?
Last edited by bearfoil; 31st May 2011 at 02:42.