Slitherine

I'm a beginner in PC2, and have been trying the Crete tutorial scenario (a few times). After defeating the Allied airforce, I'd like to convert my fighters to bombers, but haven't been able to disband the fighters. According to Google (I might have found this somewhere in these forums), I need to have the fighters at the airbase, then move them to a supply hex adjoining the airbase. In the next turn, they won't automatically return and be re-assigned randomly to the airbase and surrounding hexes, so they should remain on the supply hex and it should be possible to disband them.

Everything works except the last step, meaning the air unit does remain on the adjacent supply hex after being moved there, but I'm still unable to disband it. Is there something else I should be aware of? Or does the scenario specifically disallow disbanding of air units? Or something else?

Units can only be disbanded during placement [Turn 0].
The instruction you are following are for upgrading. You 'upgrade' your Fighters to TB, not disband and buy.

Don't know how I posted this topic twice. I'll continue on the other thread.