All civil, private aircraft entering the U.S. must first land at an airport of entry before continuing to their destinations, unless other arrangements are made with U.S. CBP. Advance notification must be provided electronically to CBP by means of the eAPIS. See the APIS section for more information.
Customs will expect aircraft to land at the arrival time entered on their flight plan. Arriving up to 10 minutes late is acceptable. Passengers and crew should remain with the aircraft until a Customs official arrives and be prepared to show valid documents for persons and aircraft.
Some aircraft arriving from foreign locations south of the United States must land for Customs processing at the nearest airport to the border or coastline crossing point, unless an overflight exemption has been granted (CFR Title 19, 122.24).
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https://www.faa.gov/air_traffic/publications/us_restrictions/airspace/