Per FAA?? Where is that written???  

§135.601   Applicability and definitions.

(a) Applicability. This subpart prescribes the requirements applicable to each certificate holder conducting helicopter air ambulance operations.

(b) Definitions. For purposes of this subpart, the following definitions apply:

(1) Helicopter air ambulance operation means a flight, or sequence of flights, with a patient or medical personnel on board, for the purpose of medical transportation, by a part 135 certificate holder authorized by the Administrator to conduct helicopter air ambulance operations. A helicopter air ambulance operation includes, but is not limited to—

(i) Flights conducted to position the helicopter at the site at which a patient or donor organ will be picked up.

(ii) Flights conducted to reposition the helicopter after completing the patient, or donor organ transport.

(iii) Flights initiated for the transport of a patient or donor organ that are terminated due to weather or other reasons.

(2) Medical personnel means a person or persons with medical training, including but not limited to flight physicians, flight nurses, or flight paramedics, who are carried aboard a helicopter during helicopter air ambulance operations in order to provide medical care.

(3) Mountainous means designated mountainous areas as listed in part 95 of this chapter.

(4) Nonmountainous means areas other than mountainous areas as listed in part 95 of this chapter.