Great domain in my opinion. I occasionally visit the local flying club and there are always notices advertising light aircraft or shares in light aircraft for sale. There are existing sites that offer classifieds, but there's probably still room in the market. My dad has a PPL and I started my journey towards my PPL(H) until it got too expensive... learning to fly helicopters is significantly more expensive than planes! There's a lot of demand for training, equipment, or even just experiences.
I've got airstrips.co.uk and have often thought an airstrip directory would be useful, though since buying many years ago other people have attempted it so I have focused on other things.
All I'd say is it's a very specialist market. But if you can get into flying clubs you're marketing is sorted. What were you thinking of doing with it?