What about a helicopter! You could use the Barckley brothers one. In my mind its down to three possible options 1) twoter already on UK register, 2) Dornier 228 again already on UK register - or - 3) You could down grade the capacity and use an Islander. Any of the above options will not require a runway extension. However there is still the potential issue of the lack of Jet A1 on Alderney.