NFHS
A1 has the ball in A's frontcourt and passes to A2 who is airborne from backcourt, catches the ball while airborne and lands in frontcourt. I recall reading a similar case but can't find it in the book so I'm thinking I saw it on one of the many pre-tests I took in the fall.
Is this a backcourt violation and if so what's the reference?

It is a violation because A2 (still) has backcourt status.
While airborne, your status is where you last touched the floor. The reference is Rule 4-35 Art. 3 (Player Location).
Also, Rule 9-9 (Backcourt) Art. 1.