Originally Posted by
11K-AVML
I did wonder if there was some kind of mistake with the resetting to a A1000 or similar at first, but this wasn't the case - it actually changed the the Mode A to that of another aircraft and so there were two a/c with the same call signs present. Very uncommon I know. I also know that both these aircraft were airbourne at the same time.
A1000 is the
Mode S conspicuity squawk. If the aircraft doesn't need a discrete Mode A code because it is being tracked using Mode S flight ID, it (along with any others) can be assigned A1000.
The only reason I can think of for reassigning in flight is to release the discrete Mode A code for re-use. But I have no idea if that is actually done, and final approach seems like a bad place to request it.