Air-to-Air is a little bit ambiguous because there are ground units which can be airborne. For example, an ASF can execute a strike (+2 penalty) against a VTOL (which may impose a significant TMM penalty) when it is airborne. The VTOL firing back in turn suffers no TMM, but it does have an angle of attack modifier and suffers an AMM when using cruise speed. To avoid ambiguity, you need to be precise about whether it's an aerospace unit (Aerospace fighter, but also conventional fighter, airship, or dropship) or an airborne ground unit (VTOL, WIGE, or oddball battle armor).