14 CFR § 121.389

No certificate holder may operate an airplane outside the 48 contiguous States and the District of Columbia, when its position cannot be reliably fixed for a period of more than 1 hour, without—

A flight crewmember who holds a current flight navigator certificate; or

Specialized means of navigation approved in accordance with § 121.355 which enables a reliable determination to be made of the position of the airplane by each pilot seated at his duty station.

Notwithstanding paragraph (a) of this section, the Administrator may also require a flight navigator or special navigation equipment, or both, when specialized means of navigation are necessary for 1 hour or less. In making this determination, the Administrator considers—

The speed of the airplane;

Normal weather conditions en route;

Extent of air traffic control;

Traffic congestion;

Area of navigational radio coverage at destination;

Fuel requirements;

Fuel available for return to point of departure or alternates;

Predication of flight upon operation beyond the point of no return; and

Any other factors he determines are relevant in the interest of safety.

Operations where a flight navigator or special navigation equipment, or both, are required are specified in the operations specifications of the air carrier or commercial operator.