The rules for dropping troops during game play begin on page 90 of AS.
IRT High altitude drops: air-to-air attacks are explicitly permitted against dropping troops.
Attacks Against Dropping Units: Standard air-to-air attacks
(but not ground-to-air attacks) may be made against dropping
units during the turn they are on the Radar Map. These attacks
apply the normal air-to-air combat rules, but do not apply the
airborne aerospace target modifier. In the turn the dropping
units arrive on the ground map, they may be attacked as normal
ground units, but apply a +3 target to-hit modifier in place of the
unit’s normal target movement modifier.
The text prior to this paragraph establishes that the language referring to a unit from which troops were dropped is the "transporting unit", which means "dropping units" must be referring to the dropped troops. In that window of time where aerospace units may shoot up dropping troops whilst they are still airborne, the quoted rules are basically saying "treat it like any other air-to-air engagement". It doesn't mention omitting making the standard engagement control check, but it seems pretty off for the dropped troops to be required (much less
able) to maneuver and jockey for position in a dogfight...
1) Should the engagement control check be waived in the instance of aerospace units attacking dropping units that are still on the radar map?
2) If there is no engagement control check, then how is the range for such attacks established?
