49 CFR § 175.704 - Plutonium shipments.
Shipments of plutonium which are subject to 10 CFR 71.88(a)(4) must comply with the following:
(a) Each package containing plutonium must be secured and restrained to prevent shifting under normal conditions.
(b) A package of plutonium having a gross mass less than 40 kg (88 pounds) and both its height and diameter less than 50 cm (19.7 inches) -
(1) May not be transported aboard an aircraft carrying other cargo required to bear a Division 1.1 label; and
(2) Must be stowed aboard the aircraft on the main deck or the lower cargo compartment in the aft-most location that is possible for cargo of its size and weight, and no other cargo may be stowed aft of packages containing plutonium.
(1) May not be transported aboard an aircraft carrying other cargo required to bear any of the following labels: Class 1 (all Divisions), Class 2 (all Divisions), Class 3, Class 4 (all Divisions), Class 5 (all Divisions), or Class 8; and
(2) Must be securely cradled and tied down to the main deck of the aircraft in a manner that restrains the package against the following internal forces acting separately relative to the deck of the aircraft; Upward, 2g; Forward, 9g; Sideward, 1.5g; Downward, 4.5g.