41 C.F.R. § 102-33.45 What is a Government aircraft?
Title 41 - Public Contracts and Property Management
A Government aircraft is one that is operated for the exclusive use of an executive agency and is a— (a) Federal aircraft, which an executive agency owns, bails, loans, or borrows; or (b) Commercial aircraft hired as commercial aviation services (CAS), which an executive agency— (1) Leases or lease-purchases with the intent to take title; (2) Charters or rents; or (3) Hires as part of a full service contract or an inter-service support agreement (ISSA).
Title 41: Public Contracts and Property Management
PART 102–33—MANAGEMENT OF GOVERNMENT AIRCRAFT
Subpart B—Acquiring Government Aircraft and Aircraft Parts
Overview
§ 102-33.45 What is a Government aircraft?

