Flight
coupons shall be honored only in sequence as shown on the passenger
coupons. Such flight coupon(s) shall not be accepted for carriage, exchange
or refund and are not valid unless accompanied by the passenger coupon.
The
use of a flight coupon renders all unused preceding flight coupons invalid,
and a flight coupon may not be honored for carriage if it appears that
a succeeding flight coupon has already been used.