Loss of Tail Rotor Thrust in Cruise Flight

TM-1-1520-238-10 Helicopter Attack AH-64A Apache Manual
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TM 1-1520-238-10 9-12 Change 9 suitable landing area can be accomplished by maintaining or increasing airspeed. The degree of side-slip and the amount of roll may be varied by changing airspeed and by varying collective pitch. Neither, however, can be com- pletely eliminated. 9.9.3 Loss of Tail Rotor Thrust in Cruise Flight. WARNING If the airspeed is allowed to approach ef- fective translational lift, the sideslip angle may become quite severe and heli- copter control may be lost. a. Continued Flight Possible. At cruise airspeeds, it may be possible that level flight at some stabilized yaw angle can be maintained. The degree of sideslip will de- pend on the airspeed and power required to maintain flight. Some left cyclic should be used to stop the slow right turn induced by loss of thrust. Care should be taken to avoid slowing the helicopter. The airspeed indicator may not provide useful information once the sideslip is es- tablished, but true airspeed, yaw angle, engine torque, and rate of climb or descent should provide the cues nec- essary to maintain flight. If yaw angle becomes excessive, reduce power and lower the nose to regain adequate air- speed. A minimum of 80 knots during a shallow approach to a roll-on landing should be maintained until approxi- mately 10 to 20 feet above the touchdown point. Begin a gradual deceleration to arrive at approximately 5 to 10 feet above touchdown as the yaw angle begins to in- crease (to the right). At this point, retard the PWR levers as necessary to align the helicopter fuselage with the landing direction. Care should be taken to use minimum collective pitch to cushion the landing during touchdown. After touchdown, the wheel brakes should be used to maintain heading and the collective should be lowered to minimize torque. 1. Airspeed – 80 KTAS minimum (until 10 to 20 feet above touchdown). 2. Wing Stores Jettison – As appropriate 3. PWR levers – Reduce as necessary (5 to 10 feet above touchdown). b. Continued Flight Not Possible. If powered flight at an airspeed sufficient to maintain helicopter con- trol is not possible, enter autorotation and CHOP collar – CHOP. In autorotation, the sideslip and roll angles may be significantly reduced by maintaining a sufficiently high air- speed to allow the fuselage to streamline. A roll-on land- ing during touchdown will minimize the required pitch ap- plication and should be used if terrain permits. Before touchdown, time permitting, the engine PWR lev- ers should be retarded to OFF. 1. AUTOROTATE. 2. CHOP collar – CHOP. 3. WING STORES JETTISON – As appropriate 4. PWR levers – OFF (prior to touchdown). 9.9.4 Loss of Tail Rotor Thrust At Low Airspeed/Hov- er. CAUTION Continuous right rotation during de- scent and touchdown can be expected. Loss of tail rotor thrust at low speed may result in extreme yaw angles and uncontrolled rotation to the right. Immedi- ate collective pitch reduction should be initiated to reduce the yaw and begin a controlled rate of descent. If the heli- copter is high enough above the ground, an attempt should be made to increase airspeed to streamline the he- licopter. This may permit continued flight with a stabilized and manageable yaw angle. If this increase in airspeed does reduce yaw angle, proceed as outlined in LOSS of TAIL ROTOR THRUST in CRUISE FLIGHT (Continued Flight Possible) paragraph 9.9.3. If the aircraft cannot be accelerated into forward flight, initiate a power-on de- scent. Collective should be adjusted so that an acceptable compromise between rate of turn and rate of descent is maintained. At approximately 5 to 10 feet above touch- down, perform a hovering autorotation by CHOP collar – CHOP or PWR levers – OFF. 1. Collective – Reduce. 2. PWR levers or chop collar – OFF or CHOP (5 to 10 feet above touchdown).

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