Quick search by citation:
10 U.S. Code § 2245 - Use of aircraft for proficiency flying: limitation
An aircraft under the jurisdiction of a military department may not be used by a member of the armed forces for the purpose of proficiency flying except in accordance with regulations prescribed by the Secretary of Defense.
(b) Such regulations—
may not require proficiency flying by a member except to the extent required for the member to maintain flying proficiency in anticipation of the member’s assignment to combat operations; and
may not permit proficiency flying in the case of a member who is assigned to a course of instruction of 90 days or more.
In this section, the term “proficiency flying” means flying performed under competent orders by a rated or designated member of the armed forces while serving in a non-aviation assignment or in an assignment in which skills would normally not be maintained in the performance of assigned duties.
Provisions similar to those in this section were contained in Pub. L. 101–165, title IX, § 9006, Nov. 21, 1989, 103 Stat. 1130, which was set out as a note under section 2241 of this title, prior to repeal by Pub. L. 101–510, § 1481(e)(3).