In my experience as a contractor, contractors are not allowed to charge for unused airline tickets. There is only a downside for purchasing nonrefundable tickets that might not be used, and no real upside from saving money, so the contractor purchases expensive fully refundable tickets. A small portion of an approved travel budget in a contract should be usable to reimburse for unused nonrefundable tickets, keeping some limit in place to avoid abuse. Alternatively, the contractor could track and report savings by comparing fully refundable to non-refundable ticket prices, and the COTR could review invoices to ensure that expensed unused nonrefundable tickets do not exceed some portion (say, 50%) of the savings.
Idea No. 11081