TM  1-1520-240-10 9-1-26            9-1-65.  Emergency Descent. CAUTION In  executing  any  emergency  descent,  re- gardless  of  engine  power  available,  it  is imperative  that  the  helicopter  be maneu- vered into a position from which a survivable landing  can  be  accomplished.  Transition from the following descent techniques into an appropriate landing attitude/airspeed/R/D should begin prior to descending below 600 feet  AGL.  The  emergency  descent  proce- dures below will result in R/D which exceed the rates displayed on the VSI. An emergency descent is a maximum performance ma- neuver in which damage to the helicopter or power plants must be considered secondary to getting the helicopter on the ground. No one procedure can be considered the best for all given situations. The pilot must consider his flight profile in selecting the emergency descent procure- ment that he will execute. RRPM greater than102 per- cent significantly increase airframe vibration and should serve as a good RRPM cure during the maneuver. The following techniques will produce the greatest R/D from higher altitude. High Speed Straight Ahead Decent: This procedure pro- duces  the  highest  (R/D),  but  also  produces  high  air- speeds which must be dissapated prior to landing. The actual  touchdown  area  may  vary  from  the  apparent touchdown point due to the glide angle change during the initial deceleration to reduce high airspeed. 1.   Thrust  control  —  Lower.  Adjust  RRPM  to maintain approximately 104 percent. 2.   Airspeed — Adjust (approximately 130 to 150 KIAS). 3.   Recovery — Initiate at or above 600 feet AGL and decelerate to 70 - 80 KIAS to enter the autorotative corridor. NOTE Allowing the RRPM to increase during decel- eration will reduce the floating effect which will occur when the deceleration is initiated. Out-of-Trim Descent: This procedure places the helicop- ter in a high R/D and allows simultaneous execution of smoke  and  fume  elimination  procedure.  In  addition,  it allows good landing area predictability. 1.   Thrust  control  —  Lower.  Adjust  RRPM  to maintain approximately 104 percent. 2.   Airspeed — Adjust to maintain approximately 100 KIAS. 3.   Trim  —  Adjust  cyclic  and  pedals  to  obtain aminimum of one ball width out of trim to the right (left pedal forward) equivalent to a bank angle of approximately 8 to 10 degrees right and a zero turn rate. 4.   Recovery  —  Initiate  at  or  above  600  feet AGL,retrim the ball to centered flight and ad- justairspeed to approximately 70 KIAS. Low Speed Maneuvering Descent. Maneuvering the he- licopter in steep turns as described below should allow the pilot to fly the helicopter over his intended area during the descent, observe his area of intended touchdown, and make adjustments as required. 1.   Thrust  control  —  Lower.  Adjust  RRPM  to maintain approximately 102 percent. 2.   Airspeed — Adjust to maintain 70 to 90 KIAS. 3.   Bank angle — Adjust as required. Bank angles of up to 60 degrees will result in thedesired rates-of-descent. 4.   Recovery — Initiate at or above 600 feet AGL. Helicopter should be returned to wings level. 9-1-66.  Autorotative Landing. a.  An autorotative landing will be accomplished after the failure  of  both  engines.  Maintain  speed  at  or  above  the minimum (R/D) airspeed in autorotation with cyclic. b.  At approximately 50 to 75 feet above ground level, apply  aft  cyclic  control  as  necessary  (not  to  exceed  2_ nose-high   altitude)   to   initiate   a   smooth   deceleration. Maintain RRPM below 108 per cent by adjusting thrust as necessary. Do not allow RRPM to decay below 91 percent prior to deceleration for touchdown. c.  At   approximately   15   feet   aft   gear   height,   apply suffucuent thrust to slow the R/D, assist deceleration, and effect a smooth touchdown in ETL. The amount of thrust applied and the rate at which it is applied will vary depending on the wind, load, and other influencing factors. Maintain the landing  attitude,  if  possible,  with  cyclic  and  thrust  until forward speed has ceased, then smoothly lower thrust until the forward landing gear touches the ground. Apply brakes as required. d.  Whenever a touchdown into the wind under fully con- trolled  conditions  cannot  be  made,  execute  a  crosswind landing. It is better to perform a crosswind landing, which can  be  executed  from  sufficient  altitude  to  stop  drift  and reduce R/D, than to continue a turn into the wind with the great possibility of a hard landing and damage to the heli- copter.  Decelerate  the  helicopter  at  the  same  altitude  as though the helicopter were making the entire approach into the wind.