How do you build an air transport on Tiberian Sun?
If you the version of your Tiberian Sun is lower than 2.0 (no Firestorm), use Category=AirTransport. It should work correctly. If you want your mod to have Firestorm and use the latest TS version, then you’ll need to use CarryAll=yes tag, but that will make the transport land and take off to unload each passenger and vehicles will also be transported by your aircraft. Unfortunately, there is no user made game patch that fixes this limitation yet on Firestorm.