WITW
Having been closely involved in airport planning processes before, I can assure you that the planning inspectors enter the process completely impartial, but their major and unequivecal remits when deciding if airport expansion is justified are:
1) the the economic justification for aviation related development compared with existing aviation infrastructure in the region along with enviromental concerns.
2) how much non aviation development the developer is applying for now, their stated position if their appeal fails, and
3) how much non aviation development could take place in the future.
It is significant that no one, not even the airport developers have commisioned surveys or investigated the cost per passenger of, for example, schedule flights to LCY, LHR or LGW, or the revenue they'd attract from air freight flown.
Perhaps they haven't done this because they know, as does anyone in the industry, that the investment required in getting the infrastucture at Carlisle back up to scratch for use by medium size jet/large turbo prop a/c, is around £25m, taking ino account the new runway, nav aids etc.
It's money that Stobart would have to justify to their shareholders, the City and to the Government - 3 out of those 3 would have grave doubts.