19 C.F.R. § 122.84 – Intermediate airport.

(a) Application. The provisions of this section apply at any U.S. airport to which an aircraft proceeds with residue cargo, and passengers, or crewmembers and their purchases not cleared by Customs. They do not apply to aircraft arriving at the last domestic port of discharge.
(b) Entry. When an aircraft arrives at the next airport, the aircraft commander or agent shall make entry by filing the:
1. (1) Abstract general declaration and manifest;
2. (2) Traveling general declaration and manifest; and
3. (3) Permit to proceed.
  The Declaration on Entry of Aircraft at Following Airport, found on the permit to proceed, shall be properly signed before filing for entry.
(c) Crew declarations. The declarations and entries, Customs Form 5129, of any crewmembers who leave the aircraft with their purchases at the intermediate airport shall be detached from the traveling general manifest. The declaration and entries are to be detached by the Customs officer in charge and are kept at the airport.
(d) Departure. When the aircraft leaves an intermediate airport carrying residue cargo, and passengers or crewmembers and their purchases are not yet cleared by Customs or another interested Federal agency, the procedure is the same as at the first arrival airport. All documents required by this section, except those detached under paragraph (c) of this secticn, shall be returned to the aircraft commander or agent for filing at the next entry airport.