Does the STC or 337 form have to be carried in the aircraft while flying?
ANSWER: An FAA Form 337 is required to be on board the aircraft when it is issued to document a fuel tank installation typically used for a ferry flights.
FAR 43, Appendix B, Paragraph (d) states:
"(d) For extended-range fuel tanks installed within the passenger compartment or a baggage compartment, the person who performs the work and the person authorized to approve the work by §43.7 shall execute an FAA Form 337 in at least triplicate. A completed copy of that form shall be—
(1) Placed on board the aircraft as specified in §91.417 of this chapter;
(2) Given to the aircraft owner; and
(3) Forwarded to the Federal Aviation Administration, Aircraft Registration Branch, AFS–751, Post Office Box 25724, Oklahoma City, OK 73125, within 48 hours after the work is inspected."
For other records (i.e., FAA Form 337) related to STC's (major alterations), they become part of the permanent records of the aircraft, but are not required to be carried on board.