14 CFR §91.223

1. (a)Airplanes manufactured after March 29, 2002. Except as provided in paragraph (d) of this section, no person may operate a turbine-powered U.S.-registered airplane configured with six or more passenger seats, excluding any pilot seat, unless that airplane is equipped with an approved terrain awareness and warning system that as a minimum meets the requirements for Class B equipment in Technical Standard Order (TSO)-C151.
2. (b)Airplanes manufactured on or before March 29, 2002. Except as provided in paragraph (d) of this section, no person may operate a turbine-powered U.S.-registered airplane configured with six or more passenger seats, excluding any pilot seat, after March 29, 2005, unless that airplane is equipped with an approved terrain awareness and warning system that as a minimum meets the requirements for Class B equipment in Technical Standard Order (TSO)-C151.
3. (c)Airplane Flight Manual. The Airplane Flight Manual shall contain appropriate procedures for—
   1. (1)The use of the terrain awareness and warning system; and
   2. (2)Proper flight crew reaction in response to the terrain awareness and warning system audio and visual warnings.
4. (d)Exceptions. Paragraphs (a) and (b) of this section do not apply to—
   1. (1)Parachuting operations when conducted entirely within a 50 nautical mile radius of the airport from which such local flight operations began.
   2. (2)Firefighting operations.
   3. (3)Flight operations when incident to the aerial application of chemicals and other substances.