19 CFR § 122.35 - Emergency or forced landing.
(2) Coming into the U.S. from a foreign area.
(b)Notice. When an emergency or forced landing is made, notice shall be given:
(c)Passengers and crewmembers. The aircraft commander or other person in charge shall keep all passengers and crewmembers in a separate place at the landing area until Customs officers arrive. Passengers and crewmembers may be removed if necessary for safety, or for the purpose of contacting Customs.
(d)Merchandise and baggage. The aircraft commander or other person in charge shall keep all merchandise and baggage together and unopened at the landing area until Customs officers arrive. The merchandise and baggage may be removed for safety or to protect property.
(e)Mail. Mail may be removed from the aircraft, but shall be delivered at once to an officer or employee of the Postal Service.