41 CFR § 301-10.108 - What requirements must be met to use a non-contract fare?
(a) Before purchasing a non-contract fare you must meet one of the exception requirements listed in § 301-10.107 and show approval on your travel authorization to use a non-contract fare; and
(b) If the non-contract fare is non-refundable, restricted, or has specific eligibility requirements, you must know or reasonably anticipate, based on your planned trip, that you will use the ticket; and
(c) Your agency must determine that the proposed non-contract transportation is practical and cost effective for the Government.
Carrier preference is not a valid reason for using a non-contract fare.