49 CFR § 192.705 - Transmission lines: Patrolling.
(a) Each operator shall have a patrol program to observe surface conditions on and adjacent to the transmission line right-of-way for indications of leaks, construction activity, and other factors affecting safety and operation.
(b) The frequency of patrols is determined by the size of the line, the operating pressures, the class location, terrain, weather, and other relevant factors, but intervals between patrols may not be longer than prescribed in the following table:
|Maximum interval between patrols|
|Class location of line||At highway and railroad crossings||At all other places|
||15 months; but at least once each calendar year.|
(c) Methods of patrolling include walking, driving, flying or other appropriate means of traversing the right-of-way.