Subsonic

Subsonic (鳳凰翼風(サブソニック)) is a small transport aircraft developed by Usamimi, introduced in Toaru Majutsu no Index Struggle Battle. It has an autopilot feature that allows the aircraft to do navigate on its own.

Background
It is seemingly made as if in jest, as it was supposed to be still kept in the laboratory and to be tested.

In the game, it was used by Usamimi and the Player to escape the institution where it was taken as it was being invaded by Anti-Skill and organizations from the Dark Side of Academy City. The dark side prepared combat helicopters to take down the aircraft but it managed to evade it. However, it was ultimately blown up by a bomb planted by Tsuchimikado Motoharu to prevent their escape, forcing the aircraft to make an emergency landing. Moreover, the long-distance navigation of the aircraft failed to work.