TM  1-1520-240-10 8-4-4            8-4-30.  Flight in Thunderstorms. Flight in or in close proximity to thunderstorms is to be avoided  because  of  the  accompanying  severe  turbu- lence and restricted visibility. If a thunderstorm is inad- vertently encountered during flight, the procedures for flight in turbulent air are to be followed and the flight path altered to leave the area. Should a thunderstorm be en- countered during a night flight, the cockpit dome light should be turned on with white light selected to minimize the  blinding  effect  of  lightning.  Refer  to  chapter  5  for limitations. 8-4-31.  Ice and Rain. 8-4-32.  Ice. The helicopter is equipped with pitot tube, AFCS yaw port heating, and windshield anti-icing systems to enable safe flight in light icing conditions. Operation of these systems is  described  in  Chapter  2.  Additional  information  and specific procedures are also included in this section un- der  Cold  Weather  Operations.  The  greatest  damage caused by ice accumulation is lowered rotor blade effi- ciency resulting in decreased range and endurance. If icing  is  encountered  during  IMC  flight,  consideration must be given to reduced range and endurance due to increased fuel consumption. Refer to chapter 5 for limita- tions. 8-4-33.  Exterior Inspection. Refer to paragraph 8-2-10. 8-4-34.  Taxiing. Taxi  at  slow  speeds  to  ensure  positive  braking  action during turns. The forward tilt of the rotors will cause the helicopter to continue moving forward if icy conditions prevent braking. 8-4-35.  Before Takeoff. When  the  takeoff  is  to  be  accomplished  into  possible icing conditions, the following are to be accomplished as part of the Before Takeoff Check. ANTI-ICE switches — ON. Refer to chapter 5 for limita- tions. 8-4-36.  During Flight. Since  all  of  the  systems  on  this  helicopter  are  of  the anti-icing rather than the de-icing type, always start sys- tems  at  least  5  minutes  before  entering  a  suspect  or forecast icing area. In addition, engine icing can occur at temperatures above freezing. a.  Extended flight in light icing conditions may result in lateral and vertical vibrations caused by asymmetric self-shedding of ice. Minor rotor blade damage may oc- cur from ice shedding at 10_C and below. One-per-rev lateral vibrations from asymmetric shedding at any tem- perature may occur. If vibrations are encountered, air- speed should be reduced and the aircraft should be flown out of the icing area. b.  Extended flight in icing conditions can result in ice accumulating on the helicopter heater fuel drain. If the heater shuts down during icing, do not attempt restart until ice is removed from the heater intake, exhaust, and heater fuel drain. 8-4-37.  Approach and Landing. Accomplish a normal approach and landing; but if icing is present, increased power will be required. The forward and aft wheels accumulate ice, which can result in the brakes freezing. If icing conditions have been encoun- tered, a zero forward ground speed landing should be accomplished. 8-4-38.  Rain. It is considered that rain will have no detrimental effect on the flight characteristics or performance of the helicopter. The windshield wipers should be adjusted to FAST dur- ing an instrument approach in rain, as rain may present a  restriction  to  visibility.  Pitot  heat  should  be  used  for flights in rain to prevent moisture from accumulating in the pitot tube and AFCS yaw ports and tubing. 8-4-39.  Salt Water Operation. 8-4-40.  Power Deterioration. Salt spray ingestion in turbine engines may result in a loss in performance as well as a loss in compressor stall margin. This reduction in stall margin makes the engine susceptible to stalls during acceleration, and more partic- ularly,  under  deceleration  conditions.  As  spray  is  in- gested  and  strikes  the  compressor  blades  and  stator vanes, salt is deposited. The resulting buildup gradually changes the airfoil sections, which in turn affects perfor- mance. This deterioration will be noticed as a decrease in torque and an increase in PTIT for a given N1. Should the deterioration reach the point where the compressor actually stalls, PTIT will increase, while N1 and torque will  decrease.  The  circumstances  under  which  power deterioration may occur during salt water operation vary with   a   number   of   factors.   The   flight   regime,   gross weight,wind direction and velocity, pilot technique, dura- tion of maneuver, salinity of the water, and the relative density of the salt spray, all have a bearing on perfor- mance deterioration. Intermittent operation in moderate salt   spray   conditions   could   expose   the   engines   to enough salt spray to cause noticeable performance de- terioration.  During  prolonged  operations  (such  as  low hovering) in heavier spray conditions, power deteriora- tion will be apparent and is more critical. Maneuvers such as hovering close to the water in light winds, or low flights at low speeds will generate maximum rotor downwash spray conditions. Careful operation, following the proce- dures and limitations contained herein, in strict adher- ence to the prescribed maintenance procedures when