Q: Air/oil cooling? A: Oil returns to the reservoir through the inlet scroll vanes. This cools the oil and provides full-time anti-ice to the scroll vanes.
Q: Start bleed / anti-ice valve? A: During start and low power a portion of the compressor air is bled at the 5th stage to prevent stalls and improve efficiency. This valve also directs air to the engine inlet for anti-ice.
Q: Anti-ice power reduction? A: Up to 18% percent power lost in normal operation. Up to 40% during a failure.
Q: Engine anti-ice bled air supply? A: With engine anti-ice on bleed air is always being supplied to the engine inlet, swirl vanes and variable inlet guide vanes. Engine anti-ice is provided to a valve that provides variable amounts of bleed air to the airframe inlet temperature dependent.
Q: APU bleed air? A: There is no valve that stops APU bleed air. Whenever the APU is running the air is available for engine starts or ECS regardless of the air source switch position (e.g. the start and ECS valves are always pressurized).
Q: Engine start valve operation? A: The engine start valve opens when the starter button is pushed. A holding circuit keeps the valve open until 52-65% Ng or the PCL is pulled down. ENG STARTER advisory indicates that the valve is open (energized).
Q: Engine bleed air shutoff valves? A: These control engine bleed air used for engine starts and ECS. Located in the piping aft of the start valves these valves are operated when the air source is set to engine. They are one-way check valves that prevent back flow when there is a significant pressure differential.
Q: Engine underpressure switches? A: These secure air from the donor engine to the ECS when pressure becomes too low.
Q: Ng sensing? A: Accomplished by the engine alternator. Sent to the MFD, ignition and decu. The HMU senses Ng separately through a mechanical connection.
Q: TGT sensing? A: Accomplished by seven thermocouples sent to the decu then to the MFD, torque motor, and overspeed/drain valve (hot start protection).
Q: Np sensing? A: Sent to the decu then the MFD and HMU/torque motor.
Q: Torque sensing? A: Accomplished by a coaxial shaft which sends signal to the decu then the MFD and torque motor as well as the other engine (torque sharing).
Q: Fire detection system? A: There are two detectors per engine compartment (one on the deck, one on the firewall) and one in the APU (fire wall only). The signal for a fire or overheat is sent to an amplifier then the associated cockpit lights.
Q: Fire extinguishing system? A: Two bottles and two ports. FWD bottle is the main for the #1 engine and the APU. AFT bottle is the main for the #2 engine.
Q: Impact switch? A: Located above the cabin door this sets off the fire bottles into each engine if over 10g’s is sensed in any direction.
Q: Extinguisher power? A: If you don’t have the #2 DC primary bus (or AC power) you only have the reserve extinguisher for the #1 and APU. You cannot fire a bottle for the #2 engine.
Q: Functions of the HMU? A: Fuel flow metering and positive cutoff, Ng governing, acceleration/deceleration flow metering, variable vane and start bleed control, collective pitch load anticipation (LDS), manual override control (lockout), and fuel priming.
Q: HMU inputs? A: PCLs, collective, and Ng drive connection, and monitors compressor discharge pressure (P3), and ambient air temp (T2).
Q: Ng spline? A: The HMU senses Ng through a spline (not the alternator). This Ng sensing is used to meter fuel and adjust the variable geometry vane servo for the variable vanes and start bleed valve. The Ng spline drives the high pressure HMU fuel pump.
Q: Lockout? A: Lockout takes away the functions of the torque motor servo. In lockout you lose TGT limiting, Np governing and load sharing.
Q: DECU? A: The decu trims the HMU for steady state operation and provides Np governing, Np overspeed protection, TGT limiting, hot start prevention, torque monitoring and load sharing, fault detection and indication, TGT, Np and torque indications. The decu sends signals via the torque motor servo amplifier to the torque motor servo for fuel flow input (various subsequent versions of the EDECU offer additional functionality such as auto contingency power and auto relight).
Q: DECU electrical power? A: The decu normally receives power from the engine driven alternator. It can also receive back up power from the aircraft’s AC power system.
Q: Contingency power? A: Contingency power increases the TGT limiting to provide more power.
Q: Np trim switch? A: Allows the pilot to adjust Np between 96-101%.
Q: DECU load sharing? A: The load sharing circuitry can increase the low engines Ng up to 3% to match the high engine’s torque (that is one of the reasons the Ng check is above 63% within 3%). Load sharing always increased the low engine to match. It never decreases the output of the high engine.
Q: Overspeed protection? A: The decu sends a signal to open the overspeed drain valve when Np is about 120%.
Q: Overspeed test? A: The overspeed threshold can be reset from 120% to 96% by pressing both A and B buttons together. In the EDECU the auto relight will be activated.
Q: ENG oil (sequence)? A: Dry sump, pump, filter bypass (cold oil relief valve to accessory module), Accessory module (pressure temp sensors/caution via VIDS), sumps (A, B, C), chip detector, fuel/oil heat exchanger, scroll vanes (air cooling), back to dry sump.
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