Thanks, gents!
Originally Posted by Rudderrudderrat
As far as I'm aware, the PVD turns itself off after liftoff and is not available in flight. It is intended purely for guidance during the take-off roll.
On this point, I was wondering if it actually turns itself off, or the shutters just close (as happens when the system is armed prior to takeoff, and before entering the runway)
"PVD unshuttered -
PVD selected on, within valid localizer region, within 45 degs of runway heading, and on ground.
The manuals say that this "ground" signal is actually a "Rad Alt < 5feet" signal sent to the Flight Control Computer which then sends this and other data to the Para Visual Display Computer. The "in air" logic is actually RA>5 feet AND groundspeed > 80kts. I can't see the sense in the 80kt logic, but this rather low airspeed logic appears in a number of different systems.