Each employee's reimbursement request shall include: The Comptroller of the Treasury's GAD Form X-3A, “Individual Request for Out-of-State Travel,” in accordance with Regulation .10 of this chapter; The Comptroller of the Treasury's GAD Form X-5, “State of Maryland Expense Account”; Itemized receipted bills and such other supporting documentation of expenses as may be required by the Comptroller. Payment for Airline and Rail Tickets (Common Carrier). The following conditions shall be effective upon written notification of the Secretary to the unit head: Units shall pay for employee common carrier tickets issued by the contractor travel service using the credit account number provided by the contractor selected for that purpose. Each unit or appropriate unit division shall be issued one account number and shall be centrally billed by the contractor for all charges. The identity of and access to all unit account numbers shall be restricted by the unit to the essential personnel. Each unit shall have a written policy and assigned responsibility for obtaining and controlling common carrier tickets. Wholly unused, fully refundable tickets shall be returned by the employee to the designated unit official to obtain credit. The unit official immediately shall return any unused portions of tickets to the contractual travel agency for credit to be applied.