Originally Posted by NW Contract of Carriage

B) NONREFUNDABLE TICKETS
1) IF, AFTER A NONREFUNDABLE TICKET/NONREFUNDABLE UNTICKETED
PREPAID TICKET ADVICE (PTA) HAS BEEN ISSUED AND BEFORE ANY
PORTION HAS BEEN USED, A DECREASE IN THE FARES OR CHARGES
APPLICABLE TO THE TRANSPORTATION COVERED BY THE TICKET (SAME
ORIGIN, DESTINATION, AND STOPOVER POINT (S) BECOMES EFFECTIVE
OR A NEW FARE FOR WHICH THE PASSENGER CAN QUALIFY BECOMES
EFFECTIVE THE PASSENGER WILL RECEIVE THE DIFFERENCE IN FARES
IN THE FORM OF AN MCO/TRAVEL CREDIT VOUCHER AFTER SUBTRACTING A
USD50.00 ADMINISTRATIVE SERVICE FEE.
ONCE A DECREASE IN THE FARES/CHARGES AND/OR THE ADDITION OF A NEW
FARE HAVE BECOME EFFECTIVE, THE ORIGINAL TICKET MUST BE REISSUED
AND ALL CONDITIONS OF THE DECREASED FARES/CHARGES OF THE NEW FARE
MUST BE MET INCLUDING ADVANCE RESERVATION/BOOKING CODE/TICKETING
REQUIREMENT.
NOTE: 1. AN MCO IS NONTRANSFERABLE.
2. MCOS MAY BE USED AS PAYMENT FOR AIR TRAVEL OR TRAVEL
RELATED SEVICES ON NWA.
3 .MCOS REDEEMED FOR TRAVEL OR TRAVEL RELATED SERVICES
MUST BE REDEEMED OR EXCHANGED FOR A TICKET WITHIN
ONE YEAR OF THE MCO ISSUE DATE.
4. PARTIALLY USED MCOS WILL NOT HAVE RESIDUAL VALUE.