I think He/She should:
Write to the owners of the former airport, informing them that, since they refused to allow him to remove the aircraft from their property by the most expeditious/economical means available,(by air) they became responsible for the safe keeping of the aircraft, and for any damage/deterioration occurring during it's unlawful detention.
Call the Police, and report the aircraft stolen.
Make
every effort to publicise the situation.
MJ
Ps. All of the above assumes that there isn't more to the situation than meets the eye, which there probably is.