(a) Generally. Preliminary entry allows a U.S. or foreign vessel arriving under circumstances that require it to formally enter, to commence lading and unlading operations prior to making formal entry. Preliminary entry may be accomplished electronically pursuant to an authorized electronic data interchange system, or by any other means of communication approved by the Customs and Border Protection (CBP).

(b) Requirements and conditions. Preliminary entry must be made in compliance with § 4.30, and may be granted prior to, at, or subsequent to arrival of the vessel. The granting of preliminary vessel entry by Customs at or subsequent to arrival of the vessel, is conditioned upon the presentation to and acceptance by Customs of all forms, electronically or otherwise, comprising a complete manifest as provided in § 4.7, except that the Cargo Declaration, CBP Form 1302, must be presented to Customs electronically in the manner provided in § 4.7(b)(2) or (4). Vessels seeking preliminary entry in advance of arrival must do so: By presenting to Customs the electronic equivalent of a complete CBP Form 1302 (Cargo Declaration), in the manner provided in § 4.7(b)(2) or (4), showing all cargo on board the vessel; and by presenting CBP Form 3171 electronically no less than 48 hours prior to vessel arrival. The CBP Form 3171 will also serve as notice of intended date of arrival. The port director may allow for the presentation of the CBP Form 1302 and CBP Form 3171 less than 48 hours prior to arrival in order to grant advanced preliminary entry if a vessel voyage takes less than 48 hours to complete from the last foreign port to the first U.S. port, or if other reasonable circumstances warrant. Preliminary entry granted in advance of arrival will become effective upon arrival at the port granting preliminary entry. Additionally, Customs must receive confirmation of a vessel's estimated time of arrival in a manner acceptable to the port director.