TM  1-1520-240-10            8-4-1 SECTION  IV.  ADVERSE ENVIRONMENTAL CONDITIONS 8-4-1.  Cold Weather Operation. Refer to FM 1-202, Environmental Flight. 8-4-2.  General. Operating the helicopter in an environment of extreme low temperature and the associated weather phenome- na requires that certain techniques and operating proce- dures be implemented in addition to the normal operating procedures in Section II. The following operating tech- niques and procedures have been developed from actu- al arctic flight testing and other pertinent information. 8-4-3.  Preparation for Flight. The following additional exterior checks are to be per- formed during cold weather operation. a.  Check that all ice, snow, and frost have been re- moved from the exterior surfaces, particularly the rotor blades. CAUTION Ice  removal  should  never  be  accom- plished by chipping or scraping. Deicing fluid should be used. b.  Landing gear shock struts, wheel brakes and flight control  system  actuators  should  be  checked  to  make certain that exposed piston areas are free of dirt, ice, etc. c.  While   checking   the   engines,   the   compressor should  be  manually  checked  for  freedom  of  rotation. Heat must be applied if the compressor is frozen. d.  When operating the ramp, it may be necessary to cycle it once or twice to achieve proper closure. e.  Ensure that the manually operated vent valves on the rotary-wing shock absorbers are open at tempera- tures below –18_C. At temperatures between –18_C and –1_C, the vent valves may be opened or closed. At tem- peratures above –1_C, the vent valves must be closed. f.  If seasonal temperatures are +4_C and below, the aft rotor droop stop shrouds should be installed. g.  At temperatures below –18_C, preheating aircraft is recommended for a minimum of 1–1/2 hours. Empha- sis should be placed on engine fuel control units. h.  Refer to Chapter 5 for icing limitations. 8-4-4.  Heater Normal Operation. CAUTION Cycling of the heater blower may disable power steering control. a.  Starting. 1.  Inlet and outlet coverers — Remove. 2.  BATT switch — ON. 3.  APU — Start (para. 8-2-18). 4.  APU GEN switch — ON. RECT OFF caution capsule extinguishes. 5.  R (right) MAIN FUEL PUMP switches — ON (only if heater is to started). CAUTION Pull the cockpit air knobs slowly to pre- clude dirt and debris from being blasted into the air and pilot’s eyes. 6.  Push in the air control knobs. 7.  Heater function switch — As desired (BLWR ONLY or HTR ON if BLWR only, steps 8 and 9 below do not apply). 8.  HTR START switch — Press. NOTE If the left side of the helicopter is exposed to the sun, the cabin thermostat may be heated to 34_C which is sufficient to prevent starting the heater. 9.  CABIN TEMP SEL switch — As desired. b.  Heat Distribution. 1.  For  maximum  cockpit  heat  proceed  as  fol- lows: (a)  Pilot and copilot cockpit air control knobs — Pull. (b)  DEFOG or DEFROST handle — Pull. (c)  CABIN AIR handle — Push. (d)  CABIN TEMP SEL switch — Full clock- wise. 2.  For maximum cabin heat proceed as follows: (a)  Pilot and copilot cockpit air control knobs — Push. (b)  DEFOG or DEFROST handle — Push.