Others have said that a telescope suitable for astronomy would be overpowered for viewing aircraft, but this isn't true. Manually keeping aircraft in the field of view would be difficult, but you can use software to automatically steer a computer-controlled telescope and get great results.
For example, here's a photo of an aircraft being tracked by the tracking application OpticTracker:
This demo video shows both a Meade LX200 and a Celestron NexStar 4E being used with OpticTracker to track various aircraft.
There may be other tracking applications out there; OpticTracker is just one I've researched. In order to select an appropriate telescope, I would start with the requirements for whatever tracking software you're considering using. For example, you can see the list of telescopes compatible with OpticTracker on the compatibility page.