19 CFR 122.26: Entry and clearance.

Private aircraft, as defined in § 122.1(h), arriving in the United States as defined in § 122.22, are not required to formally enter. No later than 60 minutes prior to departure from the United States as defined in § 122.22, to a foreign location, manifest data for each individual onboard a private aircraft and departure information must be submitted as set forth in § 122.22(c). Private aircraft must not depart the United States to travel to a foreign location until CBP confirms receipt of the appropriate manifest and departure information as set forth in § 122.22(c), and grants electronic clearance via electronic mail or telephone.