Dan Truesdell wrote in news:40BBB5F8.1090404
@ceaPLsofAtwNarEe.cSom:

Unless I'm mistaken, I believe that you need to have an "official" clock
in the plane to fly actual. Doesn't mean that you have to use it, but I
believe it has to be there and has to be working. We are replacing ours
right now. (Seems like a silly reg.)

Why is that silly? Imagine... You're holding over your MAP point waiting
for your next opportunity to shoot. All of a sudden, the battery in your
watch decides to go out. What do you do then? Without the clock in the
plane, you'd probably have to inform ATC and become a real PITA...

Yeah, it might be a longshot, but Murphy's law dictates that if the battery
is going to die in flight, it's going to happen during a critical point...