Now, the automatic speed protection you mention applies if VLS is approached from above, but would it apply if the airspeed is already and suddenly well below VLS ?
Also, such automatic speed protection applies for a climb scenario. Would the FDs command a temporary descent in order to get back to VLS ?
CONF: This is as you say definitely interesting.
The specific failure mode that put you into alternate law will determine whether VLS is computed and displayed or not.
From simulations (using manual deselection & reselection of the FD's), if the failure mode does not preclude computation and display of VLS on the PFD with an operative FD then the following appears to apply:
1. If above VLS and decelerating when the FD's are reselected, the FMA vertical mode will default to VS and display the current VS and the FD pitch bar will command that specific VS (i.e. +1500) until such time that VLS is reached and then command nose down (
decrease in pitch) to honor VLS. The FMA annuciation will remain VS with the displayed command (i.e. +1500) that was in effect when the FD was reselected even though the pitch bar is honoring VLS.
2. If below VLS when the FD's are reselected, and VLS computations available, the pitch bar will immediately command nose down (
decrease in pitch) to honor VLS, but the FMA will still default to VS and display the specific rate in effect at the time the FD's were reselected (i.e. +400, etc.)
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If the failure mode responsible for alternate law precludes computation and display of VLS (i.e. VSW only zipper with flap position sensor problems and VLS dashes on the PERF page), then the following appears to apply:
1. Regardless of whether above or below the actual but uncomputed and undisplayed VLS, when the FD is reselected, the system will default to VS and the current rate (i.e. +1500) and the pitch bar will command that rate right into the stall,
if followed.
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I would guess that recovery from actual dual or triple ADR problems that result in 'latched' ALT 2 would result in no VLS computation or display but I'm not positive. Maybe you or
A33Zab would know.
Simulations that allow for dual or triple ADR failure are directed at the failure remaining in effect until landing so that if the ADR's are 'revived' the aircraft returns to normal, not latched ALT 2.
Possibly a new simulation requirement? I'm always in the market for good tech info.
