Control of fuel to the combustion system is provided by the HMU. The HMU, mounted on the rear center of the accessory gear box, contains a high pressure pump that delivers fuel to the ODV. Various parameters are sensed by the HMU and influence fuel flow, variable geometry position, and engine anti-ice start bleed valve operation. There are two mechanical inputs from the cockpit to the HMU. The load demand system provides mechanical input directly from the collective output of the flight control mixer to the engine HMU to reduce transient engine and NR droop. This system acts as a load anticipator that immediately inputs a load change to the HMU, which resets NG as required to maintain a nearly constant NP. This system makes gross corrections which are fine-tuned by the load sharing and power turbine governing functions of the DEC. If the ENG POWER CONT lever is moved to LOCKOUT and then to an intermediate position, the engine will still vary power in response to collective signals. Collective movement is transmitted directly to the MMU. A bellcrank on the mixer provides input to the push-pull load demand spindle (LDS) cables, and then to the engine HMUs via a rotary actuator. The rotary actuator is spring loaded to increase the collective direction to minimize system freeplay, and will also drive the LDS to maximum demand (corresponding to full up collective), in case of a separation in the system, resulting in full engine power available. At the mixer end of the cable, a shear pin/roll pin is provided to prevent a flight control jam in the event of a load demand system malfunction. If the pin shears, the LDS cable to the HMU for that engine will drive full aft and produce the maximum LDS demand. This may under certain flight conditions produce a torque split. If the pin shears and the load requirement of the engine is reduced (e.g., an autorotation) the DEC will not have enough down trimming authority to reduce torque to zero. Under this condition the excess engine torque produced may be sufficient to drive the engine or NR to NP1 or NP2 overspeed.

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The ENG POWER CONT lever operates the Power Available Spindle (PAS) in the HMU. When the engine is operating in FLY, the LDS and DEC control have maximum power available to be utilized. If the ENG POWER CONT lever is placed in LOCKOUT, the NP1 or NP2 servo normally controlled by the DEC is locked out to its maximum power position. Engine power must now be set manually by adjusting the ENG POWER CONT lever. The engine will still 17

 increase/decrease power in response to (LDS) collective changes. DEC/EDECU functions which utilize the NP1 or NP2 servo (TGT limiting, NP1 or NP2 governing, LOAD sharing) are inoperative in LOCKOUT.

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WARNING

Going to DEC LOCKOUT to obtain additional power does not remove Maximum Fuel Flow or NG limits. NR may still decrease below normal operating range if Maximum Fuel Flow or NG limits are reached.

NOTES concerning engine indications

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The change in the engine oil temperature lower limit of (-20°C) is not an actual temperature / functional limit change; it is based on the physical reporting limits of the Engine Instrument Caution Advisory System (EICAS). The indication is not reportable below (-20°C).

The UH-60M DEC/EDECU bias has been changed to -112°C, this provides for similar displayed limit indicating numbers when compared to the UH-60L. The UH-60L was biased to show lower than actual indicating numbers on the central display unit due to the display’s inability to show four digit numbers. On the UH-60M TGT display an indication of 903°C is in reality 1015°C actual temperature.