Maybe try this:

Exceptions to the Fly America Act

There are some circumstances where it’s not reasonable to use a U.S. flag air carrier, and you can make an exception to the Fly America Act. These circumstances are:

1. When a U.S. air carrier is not available.
2. When using a U.S. carrier service would extend the travel time by 24 hours or more.
3. When a U.S. carrier does not offer a nonstop or direct flight between origin and destination, and using a U.S. carrier:
   • Increases the number of aircraft changes outside the United States by two or more;
   • Extends travel time by six hours or more; or
   • Requires a connecting time of four hours or more at an overseas interchange point.
4. When the flight time from origin to destination is less than three hours and using a U.S. flag carrier doubles the flight time.
5. When there is an applicable Open Skies Agreement in effect that meets the requirements of the Fly America Act.

The exceptions provided by the Open Skies Agreements for government-funded travel do not apply if your transportation is funded by the Department of Defense (DOD).

Note: Ticket cost and convenience are NOT exceptions to the Fly America Act.