TM 1-1520-238-10 Change 10 9-9 9.5.4 Dual Engine Failure. WARNING In the event of an inadvertent activa- tion of the engine chop collar, initial in- dications from N_P and N_r could be in- terpreted as a dual engine failure. Indications of engine chop collar ac- tivation are the ENGINE CHOP light il- luminates and engine idle indications on the N_G, TGT and N_P. There is NO illu- mination of the ENGINE OUT 1 or 2 lights on the MASTER CAUTION panel. If both engines fail, immediate action is required to make a safe autorotative descent. The altitude and air- speed at which a two engine failure occurs will dictate the action to be taken. After the failure, main rotor rpm will decay rapidly and the aircraft will yaw to the left. Un- less a two-engine failure occurs near the ground, it is mandatory that autorotation be established immediate- ly. At gross weights above 15,000 lbs, immediate con- sideration should be given to jettisoning the external wing stores. During cruise at airspeeds to V_ne, reduce collective immediately to regain N_r and then adjust as required to maintain rpm. The cyclic should be adjusted as necessary to attain and maintain airspeed in the opti- mum range (fig 9-3). An airspeed between 64 and 98 KIAS should be maintained except for high altitude high gross weight conditions where the maximum allowable autorotation airspeed should be maintained if it is less than 64 KIAS. A landing area must be selected immedi- ately after both engines fail, and control inputs must be made to fly to the intended site. Throughout the de- scent, adjust collective as necessary to maintain N_r within normal range. At high gross weights, the rotor may tend to overspeed and the collective must be used to maintain the desired rotor rpm (fig 5-1). N_r should be maintained at or slightly above 100% to allow ample rpm before touchdown, and heading maintained by pedals. Main rotor rpm will increase momentarily when the cy- clic is moved aft with no change in collective pitch set- ting. An autorotative rpm of approximately 100% pro- vides for a good rate of descent. N_r above 100% may result in a higher than desired rate of descent. At 100 to 125 feet AGL, use aft cyclic to decelerate. This reduces airspeed and rate of descent and causes an increase in N_r. The degree of increase depends upon the amount and rate of deceleration. An increase in N_r can be desir- able in that more inertial energy in the rotor system will be available to cushion the landing. Ground contact should be made with some forward speed. If a rough landing is selected, a more pronounced deceleration is necessary and touchdown speed should approach zero. It is possible that during the autorotative approach, the situation may require additional deceleration. In that case, it is necessary to assume a landing attitude at a higher altitude than normal. Should both engines fail at low airspeed, initial collective reduction may vary widely. The objective is to reduce collective as necessary to maintain N_r within normal range. In some instances at low altitude or low airspeed, settling may be so rapid that little can be done to avoid a hard-impact landing. In that case, it is critical to maintain a level landing attitude. Cushion the landing with remaining collective as heli- copter settles to the ground. 9.5.5 Dual Engine Failure Low Altitude/Low Air- speed and Cruise. 1. AUTOROTATE. 2. Chop Collar – Reset (only if ENGINE CHOP light is illuminated) 3. STORES JETT switches – Activate as desired (time permitting) 9.5.6 High RPM Rotor (Warning Light On) N_P Failed High. 1. Collective – Adjust to Maintain N_r within limits. If condition persists: 2. PWR lever (affected engine) – Retard to equalize torque on both engines. 3. LAND AS SOON AS PRACTICABLE. 9.5.7 Low RPM Rotor (Warning Light On) N_P Failed Low. 1. Collective – Adjust to Maintain N_r within limits. If condition persists: 2. PWR lever (affected engine) LOCKOUT – then retard to equalize torque output of both engines. NOTE Advancing the PWR lever of the engine with low torque and TGT to LOCKOUT locks out the signal from the ECU orDECU . The engine must be controlled manually to ensure that it does not exceed operating limits. LOW ROTOR RPM indications may be the result of one or both 701 or 701C engines having entered a perfor- mance–limiting condition. Refer to paragraph 9.5 Engine Failure and En- gine Power Loss. If manual control is not possible: 3. PWR lever (affected engine) – IDLE. 4. LAND AS SOON AS PRACTICABLE.