You may use a reduced group or charter fare when your agency has determined, on an individual case basis before your travel begins, that use of such a fare is cost effective. Chartered aircraft are subject to the same rules as Government aircraft, and agencies in the executive branch of the Federal Government are subject to the requirements of Office of Management and Budget (OMB) Circular A-126 and 41 CFR part 102-33 in making such cost effectiveness determinations.
41 C.F.R. §301-10.124