I believe the same weekend coincides with a paradropping event of some description.
However, not wishing to put anyone off, there isn't actually a great deal at Carlisle worth coming over to see (except the fab scenery). Some rusty, sorry-looking, badly maintained old hulks they call an air museum, a bar/cafe that closes early, and that's about it. The people are generally friendly and helpful, but they are rather anal about hi-viz jackets.
If the fly-in happens to be well attended that would be great, especially as the airfield is hardly thriving at the best of times. It always seems like the kind of place you go because you need to, rather than because you want to.
Shame really.