My understanding, on which I'd be happy to be corrected, is that the same applies as to battlefields and shipwrecks where life was lost. You may visit and view them, but not disturb them.
The book mentions the wing centre-section of a USAAF C47 visible at a spot where there had been a number of fatal crashes in the Carnedd range, which wouldn't be all that far from RAF Valley. Again according to the book, after being visible for several decades (which presumably means into the 1970) it fell into Llyn Dulyn
Llyn Dulyn . Might that be it?
G