A MCO is a miscellaneous charge order issued by either the airline or agency to process the payment of travel arrangements, usually to pay for services other than airfares. (i.e. can be used for residual balance for future travel, paper ticket fees, tour payments, etc.) If you’ve been issued an MCO by CheapAir.com, you will need to call our offices at 1-800-243-2724 to use it. Rules and restrictions apply.