14 CFR §135.609

1. (a)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:
2. (b)A certificate holder may designate local flying areas in a manner acceptable to the Administrator, that must—
   1. (1)Not exceed 50 nautical miles in any direction from each designated location;
   2. (2)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
   3. (3)Take into account the operating environment and capabilities of the certificate holder's helicopters.
3. (c)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.