The good thing for you is that you know you are dealing with an End User. Hence, you shouldn't ask for a wholesale price or the amount you would normally charge another domain reseller/webmaster. On the other hand, I don't think the name is very valuable. (Of course, I do not know the aviation credit field very well.)
Considering both the good and bad, I'd be ambitious with an asking price - but not too ambitious as to scare off a rare potential buyer for the domain. You may consider trying to fish an offer from them first. Something along the lines of...
"I may be interested in parting with this domain for a reasonable price. Please submit your offer, etc."
This will give you an indication of how serious they are about owning this domain. Most likely they won't give you their top offer to start off with, but it will get the ball rolling. Then you can see how they respond and go from there.
Good luck.
