In the Campaign it is possible to right click on a base and choose "add package". This could be convienient so that you could choose a base close to the FLOT and not have to fly 100 miles to get into a combat area.

It allows you to choose your takeoff time and then click on New and it brings up the "add flight" menu and you choose the type of aircraft you want and how many in the flight, etc. It appears to be allowing you to add a flight on the base of your choice.

But when you hit OK on the add flight screen you get a message "no aircraft available".

I am now assuming that this is not possible

Anyone know anything about this

It's because the game is using all available aircraft. You should unset the "set by HQ" for this squadron, then you can create flights.