41 C.F.R. § 102-33.255
Declassify a Federal aircraft
(a) To declassify a Federal aircraft, you must send a letter to the Deputy Associate Administrator, GSA, requesting approval to declassify the aircraft, stating it is non-operational. Include the following:
(1) Relevant Federal Supply Classification (FSC) groups, if applicable; and
(2) Description of the aircraft's condition.
(b) When an aircraft is lost or destroyed, or is otherwise non-operational and you want to retain it, you may declassify it and remove it from your Federal aircraft inventory.