Here is the relevant paragraph from the rules
Quote:
4.1.1 Aerospace Formations
Aerospace units are organised into formations just like
any other unit. However, although aerospace formations
do receive Blast markers, they cannot be broken or
suppressed. In addition, they can’t be assaulted, lend
support to an assault or be used by another formation to
claim a crossfire, etc, while in the air. Once landed, an
aerospace unit may be assaulted and be used in a
crossfire, and is affected by Blast markers normally.