TM 1-1520-238-10 Change 9 9-5 9.5 ENGINE FAILURE AND ENGINE POWER LOSS–GENERAL. The various conditions under which an engine may fail or experience a power loss, prevent a standard procedure for all cases. A thorough knowledge of both emergency procedures and flight characteristics will enable the pilot to respond correctly and automatically in an emergency. Engines may fail partially, or performance limit, and the degree of the failure/amount of power loss is factored into crewmember response. The engine instruments often provide ample warning of an impeding failure by deviating from normal indications. An impending engine TGT limiter activation will not provide any cues prior to functioning. During performance–limiting the engine(s) will continue to display normal Ng and oil pressure indications, and as power demand increases, Np and Nr will collectively decay, TGT will remain at the engine limiter setting and torque indications will vary as a result of collective manip- ulation. Engine failure is normally indicated by a rapid drop in Ng, Np, torque, TGT, oil pressure, and the symbol- ic torque value will flash when there is a difference in torque greater than 12% between both engines. The EN- GINE OUT 1 or 2 warning lights will illuminate and an au- dio signal will be heard through both headsets. A partial engine power loss may follow certain mechanical failures, such as an ECU/DECU malfunction, or an opera- tor may induce demands that exceed an engine’s perfor- mance capabilities. An engine’s performance may envi- ronmentally (high ambient temperature, high pressure altitude/gross weight) limit as a result of: 1) TGT, 2) fuel flow and 3) Ng speed. When a loss of rotor RPM and/or a performance limitation is encountered, the pilot on the controls should immediately: 1) Adjust the collective to maintain Nr within limits and as the condition warrants, 2) jettison the aircraft wing stores. The jettisoning of the wing stores will immediately reduce the aircraft’s gross weight, power requirements and minimum single–engine air- speed values. Additionally, at low airspeeds the pilot on the controls should coordinate flight into the prevailing wind. When practical, consideration may be given to mak- ing a right banking turn and/or a right pedal turn to aid in reducing the immediate power requirements. A left bank- ing turn or left pedal turn will require more power. Proper use and understanding of performance planning calcula- tions will significantly reduce the potential for inducing en- gine performance limiting factors. Caution must be exer- cised when operating close to an engine performance limit. For example, when operating near the dual engine TGT limiter setting, a gust of wind from the aircraft’s rear or left or an activation of the engine anti–ice could result in a reduction of available power. The aircrew should not en- gage attitude/hover hold when operating near the dual en- gine TGT limiter setting. When an engine fails completely, the engine PWR lever and FUEL panel switch of the failed engine should be turned OFF. The reduction required in collective after en- gine failure will vary with altitude and airspeed at the time of failure. For example, the collective should not be re- duced when an engine fails while the helicopter is hover- ing below 15 feet. During cruise flight, when altitude and airspeed permit a significant reduction in collective pitch, N_r can be restored to 100% before landing. During single- engine flight or during autorotation airspeed should be kept at the optimum. Optimum autorotation airspeeds are shown in figure 9-3. In autorotation, as airspeed increases above 70 – 80 KIAS, the rate of descent and glide dis- tance increase significantly. As airspeed decreases below 64 KIAS, the rate of descent will increase and glide dis- tance will decrease. Autorotation during an out-of-trim condition will increase the rate of descent and decrease the glide distance. 9.5.1 Engine Failure Flight Characteristics. The flight characteristics and the required crewmember con- trol response after a dual engine failure are similar to those during a normal power-on descent. Full control of the helicopter can be maintained during autorotational de- scent. When one engine has failed, completely or partially, the helicopter can often maintain altitude and airspeed un- til a suitable landing site can be selected. Whether or not this is possible becomes a function of such combined vari- ables as aircraft weight, density altitude and airspeed at the time of the engine failure. The jettisoning of wingstores will immediately reduce the aircraft’s gross weight, power requirements, and minimum single engine airspeed val- ues. Crewmember response time and control technique may be additional factors. 9.5.2 Single Engine Failure. CAUTION Prior to movement of either PWR lever, it is imperative that the malfunctioning en- gine and the corresponding PWR lever be identified. Proper response to an engine failure depends on various factors: density altitude, airspeed, aircraft weight, single engine performance, and environmental conditions. The SAFE region in the height velocity diagram (fig 9-2) de- fines the airspeed (in Knots Indicated Airspeed–KIAS) and wheel-height combinations at various gross weight