Disengage happens all at the same time. Thus aircrafts cannot fire each other during disengage.

Q: Do disengaging aircraft get to fire AA at each other?
A: No. Aircraft only fire AA at each other when movement ends within fire arc of AA weapons, not simply passing through as with ground flak. Disengage moves end off the board, so no AA attacks can occur.

Q: What order do aircraft disengage in?
A: It is simultaneous. As aircraft do not interact with each other during the disengage move, the order is not relevant.

Q: I have a landed aircraft that has AA attacks, so it could potentially shoot at a disengaging aircraft as a ground unit. Does it get to fire flak attacks at disengaging aircraft before it disengages?
A: No. Disengaging is simultaneous, so if the landed aircraft is disengaging it is not a ground unit when the enemy passes by and no flak attack is applicable.
If it becomes critical at some point to determine which landed aircraft are remaining in place and which are
disengaging, take turns specifying which units are disengaging and which are staying in place, then perform all the disengage moves simultaneously as normal.

2 1.4.1 Sequence of Play
Q: Can we get a Sequence of Play table that includes all the clarifications about
what happens when in the Strategy Phase and the end Phase?
A: Sure.
Strategy Phase
a) Teleports placed and all other “beginning of turn” abilities go into
effect (alternating, Higher SR chooses who goes first)
b) Roll for Strategy (simultaneous)
End Phase
1. Aircraft disengage (simultaneous)
2. Resolve criticals and other “end of turn” effects (alternating, higher
SR chooses who goes first)
3. Rally (alternating, Higher SR goes first)
4. Daemons disappear (simultaneous)
5. Check victory conditions by scenario rules (varies by scenario and
may come at a different point in the sequence)

Thank you. Then we played it false for years.

Some relevant FAQ's: