14 CFR § 135.609

Unless otherwise specified in the certificate holder's operations specifications, when conducting VFR helicopter air ambulance operations in Class G airspace, the weather minimums in the following table apply:

A certificate holder may designate local flying areas in a manner acceptable to the Administrator, that must—

Not exceed 50 nautical miles in any direction from each designated location;

Take into account obstacles and terrain features that are easily identifiable by the pilot in command and from which the pilot in command may visually determine a position; and

Take into account the operating environment and capabilities of the certificate holder's helicopters.

A pilot must demonstrate a level of familiarity with the local flying area by passing an examination given by the certificate holder within the 12 calendar months prior to using the local flying area.