19 CFR §122.43

1. (a)When required. A general declaration, Customs Form 7507, shall be filed for all aircraft required to enter under § 122.41 (Aircraft required to enter).
2. (b)Exception. Aircraft arriving directly from Canada on a flight beginning in Canada and ending in the U.S. need not file a general declaration to enter. Instead, an air cargo manifest (see § 122.48) may be filed in place of the general declaration, regardless of whether cargo is on board. The air cargo manifest shall state the following:
3. (c)Form. The general declaration shall be on Customs Form 7507 or on a privately printed form prepared under § 122.5. The form shall contain all required information, unless the information is given in some other manner under subpart E of this part.