The exceptions are:
(a) If a U.S. flag air carrier offers nonstop or direct service (no aircraft change) from your origin to your destination, you must use the U.S. flag air carrier service unless such use would extend your travel time, including delay at origin, by 24 hours or more.
(b) If a U.S. flag air carrier does not offer nonstop or direct service (no aircraft change) between your origin and your destination, you must use a U.S. flag air carrier on every portion of the route where it provides service unless, when compared to using a foreign air carrier, such use would:
(1) Increase the number of aircraft changes you must make outside of the U.S. by 2 or more; or
(2) Extend your travel time by at least 6 hours or more; or
(3) Require a connecting time of 4 hours or more at an overseas interchange point.