14 CFR § 121.121

Except as provided in paragraph (b) of this section, no certificate holder conducting supplemental operations may conduct any operation over a route (including to any destination, refueling or alternate airports) unless suitable navigation aids are available to navigate the airplane along the route within the degree of accuracy required for ATC. Navigation aids required for routes outside of controlled airspace are listed in the certificate holder's operations specifications except for those aids required for routes to alternate airports.

Navigation aids are not required for any of the following operations—

Day VFR operations that the certificate holder shows can be conducted safely by pilotage because of the characteristics of the terrain;

Night VFR operations on routes that the certificate holder shows have reliably lighted landmarks adequate for safe operation; and

Other operations approved by the responsible Flight Standards office.