davidjohnson6 - yes the population is small if we use the area given in your example and I would have agreed with you until recently. However if the Scottish Government abolish APD as they have indicated they want to I think quite a few folks would travel to save the fee, particularly if its a long haul flight and a family of 4. In this example your going to save a fortune.
Whilst I am unsure as to whether any data exists as to whether folks travel long distances we do have a recent example to draw upon. Continental lobied hard to have the NI assembly reduce APD in NI as they were loosing long haul passengers from Belfast to Dublin which of course did not have APD. I think we can draw on this example as evidence that given the chance to save a few hundred quid folks will drive a couple of hours up the road rather than 15 minutes to the local airport. Ive done it a few times myself driving to Manchester rather than flying from Newcastle to see my brother in the US as on average I can save £600 (family of 4). If APD is abolished in Scotland I would simply drive to Glasgow and save even more, its a no brainer and I live 5 minutes from Newcastle Airport terminal entrance.