Section 135.605 - Helicopter terrain awareness and warning system (HTAWS)(a) After April 24, 2017, no person may operate a helicopter in helicopter air ambulance operations unless that helicopter is equipped with a helicopter terrain awareness and warning system (HTAWS) that meets the requirements in TSO-C194 and Section 2 of RTCA DO-309.(b) The certificate holder's Rotorcraft Flight Manual must contain appropriate procedures for- (1) The use of the HTAWS; and(2) Proper flight crew response to HTAWS audio and visual warnings.(c) Certificate holders with HTAWS required by this section with an approved deviation under § 21.618 of this chapter are in compliance with this section.(d) The standards required in this section are incorporated by reference into this section with the approval of the Director of the Federal Register under 5 U.S.C. 552(a) and 1 CFR part 51 . To enforce any edition other than that specified in this section, the FAA must publish notice of change in the FEDERAL REGISTER and the material must be available to the public. All approved material is available for inspection at the FAA's Office of Rulemaking (ARM-1), 800 Independence Avenue SW., Washington, DC 20591 (telephone (202) 267-9677) and from the sources indicated below. It is also available for inspection at the National Archives and Records Administration (NARA). For information on the availability of this material at NARA, call (202) 741-6030 or go to http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html.(1) U.S. Department of Transportation, Subsequent Distribution Office, DOT Warehouse M30, Ardmore East Business Center, 3341 Q 75th Avenue, Landover, MD 20785; telephone (301) 322-5377. Copies are also available on the FAA's Web site. Use the following link and type the TSO number in the search box: http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgTSO.nsf/Frameset?OpenPage.(i) TSO C-194, Helicopter Terrain Awareness and Warning System (HTAWS), Dec. 17, 2008.(2) RTCA, Inc., 1150 18th Street NW., Suite 910, Washington, DC 20036, telephone (202) 833-9339, and are also available on RTCA's Web site at http://www.rtca.org/onlinecart/index.cfm.(i) RTCA DO-309, Minimum Operational Performance Standards (MOPS) for Helicopter Terrain Awareness and Warning System (HTAWS) Airborne Equipment, Mar. 13, 2008.