TM  1-1520-240-10 8-4-2            (c)  CABIN AIR handle — Pull. (d)  Cabin adjustable outlets — Full open. (e)  CABIN TEMP SEL switch — Full clock- wise. c.  Stopping. 1.  Heater function switch — OFF. NOTE After heating and ventilating system has been stopped with the generator(s) ON, the blower will continue to operate until the temperature within the heater combustion chamber is be- low 49_C. 2.  Wait two minutes before turning generator(s) off. 8-4-5.  Alternate  Operation  —  Heating  and  Ventila- tion System. The following paragraphs describe heating and ventilat- ing system failure modes. 8-4-6.  Vibrator Contact Failure. The  heater  may  be  equipped  with  either  a  solid  state vibrator or an electromechanical vibrator. The electrome- chanical vibrator may experience vibrator contact failure, which will result in failure of the heater to operate. Heat- ers equipped with electromechanical vibrators are identi- fied by a rotary selector switch on the heater junction box. The electromechanical vibrator is equipped with two sep- arate  sets  of  contacts  designated  NORMAL  and  RE- SERVE. Upon failure of the normal contacts, the reserve set may be brought into operation by placing the switch on the junction box to RESERVE. The junction box is on the ignition unit next to the heater. 8-4-7.  Heater Overheat Condition. If the HEATER HOT caution illuminates, proceed as fol- lows: CAUTION The  heater  function  switch  shall  remain ON while performing steps a. through c. a.  Wait two minutes for cool down. b.  HTR START switch — Press. c.  HEATER HOT caution — Monitor. The HEATER HOT  caution  light  will  not  extinguish  until  combustion chamber temperature is below 177_C and HTR START switch is pressed. 8-4-8.  Engine Starting. No special cold weather start procedures are required. 8-4-9.  Warmup and Ground Tests. Allow the engine and transmission oil pressures and tem- peratures to stabilize prior to takeoff. This will require several minutes of operation at FLT. To prevent unnecessary scratches, allow electrical wind- shield heating to completely soften frost, snow, or ice before using the windshield wipers. 8-4-10.  Taxiing. Difficulty will be encountered when taxiing on ice and snow  covered  surfaces  where  braking  action  is  poor. Taxiing on the aft gear (front wheels off the ground) is recommended;  however,  caution  should  be  taken  be- cause of the poor visibility resulting from blowing snow. 8-4-11.  Takeoff. No unusual problems are associated with either the hov- ering, rolling, or vertical type takeoffs other than the ef- fects of blowing snow and slippery surfaces. Depending on the weight of snow and ice accumulated on or in the fuselage, takeoff and overall performance can be seri- ously affected. 8-4-12.  During Flight. Initial hovering with cold hydraulic fluid may produce in- sensitive  control  inputs.  Hovering  above  10  feet  (aft wheel clearance) is recommended under these condi- tions until operation is normal. With AFCS on, light pitch and roll oscillations can be expected during the first 10 or 20 minutes of flight 8-4-13.  Descent. No unusual problems are encountered during a descent. Use windshield heat if necessary. 8-4-14.  Landing in Snow. Landing in loose snow from a hover presents the unusual problem of low visibility caused by blowing snow. This helicopter  does  not  produce  this  effect  to  any  greater extent than other helicopters; however caution should be exercised during this type landing. 8-4-15.  After Landing. Maneuvering the helicopter into a slippery parking area may be difficult to accomplish and towing may be neces- sary. Taxiing on the aft gear should not be used to posi- tion the helicopter among other parked aircraft. 8-4-16.  Engine Shutdown. No  unusual  problems  are  encountered  during  engine shutdown as long as the procedures in Section II are adhered to.