I think that you need to dig out and read the constitutions of both the sports union and the club that existed - which if you don't have it, should presumably be held by the SU.
But, I would put a small bet on that aeroplane now being the property of the SU; , and that the trustees technically (although not seriously) have failed in their duty to ensure that the ownership of the aeroplane was handed over to the SU more formally - and should do so now. They were certainly never owners of the aeroplane - the key is in the phrase "trustee" - it was in their trust, it wasn't theirs.
Presumably the flying club was wound up because it was no longer a viable club anyhow.
G