Air Support is a support perk that is available at the beginning of the game for all heroes. Air Support will cause a Battlecruiser to permanently follow you throughout the game, similar to the Battlecruiser World Event. However, the Battlecruiser given by Air Support has certain other abilities. First, it has significantly higher attack damage than standard Battlecruisers. Second, unit kills secured by the Battlecruiser count towards your kill streak and kill score. Third, the Battlecruiser is a Detector, so while it has a relatively short sight range it does offer an early form of detection useful against the early Mental bosses. Additionally, the Air Support perk causes Dusk Wings to periodically spawn, as though the player had the Dusk Wings talent. This does stack with the Dusk Wings talent.
This perk is great for those who are building armies or who like an extra helping hand in both clearing and massacre bonuses. Furthermore, the Battlecruiser is counted as a minion, so the Leadership perk will affect its damage output. Characters without consistent ways to get vision on high ground such as Tychus, Swann, or Tassadar may find it useful as a spotter when trying to push into high ground areas filled with spine crawlers.
It is commonly argued that Air Support is one of the two strongest perks in the game alongside Bug Zapper, and can effectively be taken by almost any hero. Its combination of high-ground vision, steady long-ranged DPS, and Dusk Wing AoE damage make it extremely useful for both forward pushes and difficult defensive holds.