From various posts:
If it is "PFD-limited" i.e. off scale at the bottom, you are most definitely stalled...
And yes most of the time the "bird" is off , but they had over 3 minutes to hit the button and call it up.
Most of the time - it is turned off because the SOP is to use FDs. If you turn the FDs off, you then have to press another button to turn the PFV on.
...HDG-V/S was selected on AF447, never was TRK-FPA asked by the crew.
FPA/TRK was selected at some point or they would not have had FPV FLAGS reported on the PFD.
FPV was flagged because all three ADR's were simultaneously unreliable at various times. With Airbus you need at least one good ADR to get an FPV. It is not totally inertial dependent. At any time at least one ADR became reliable, the FPV would have returned (possibly not visible), if selected. On a B737 you can fail all (both of 2) ADR's and still have a full-time FPV. It is totally inertial.
The FD does not have be turned off to select FPA/TRK. When FPA/TRK is selected, the HDG/VS dual cue steering is replaced by the FPV FD symbol and the "bird" (FPV) is "displayed".
If the FPV is offscale of the PFD when it returns, how do you know what its status is?
It is not "ghosted" or caged at the lower limit (bottom) of the PFD like a HUD FPV. It is GONE.