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For starting engines inflight, or for other conditions inflight that require high-energy ignition, the IGN switch is placed in OVRD position to supply high energy ignition power to both igniters on both engines. Engine ignition power supplied to the IGN switch for OVRD function bypasses the START switches and the fuel shutoff switches.
Continental
Rev. 12/01/00 #29 Flight Manual
OVRD and GRD START modes are powered by the DC Transfer bus. CONTIN mode is powered by left and right AC. With a loss of normal AC power, the IGN switch must be moved to the OVRD mode to provide engine ignition. There is no automatic supply of energy from the Emergency Inverter on this system.
The CONTIN mode is used for takeoff, landing, and when using engine anti-ice. The OVRD mode is used for inflight emergencies or engine restart.
Engine Oil System
Oil is pumped from the oil tank by the main oil pump and delivered to the system through an oil filter. Oil quantity is sensed in the oil tank and displayed on the OIL QUANTITY gauge. A differential pressure transmitter senses pressure on both sides of the filter. When the differential pressure reaches a predetermined value, the OIL STRAINER CLOGGING annunciator light and the MASTER CAUTION light illuminate to indicate excessive differential pressure. A pressure regulating valve maintains engine oil system pressure at approximately 45 psi. The oil is cooled as it flows through the fuel / oil heat exchanger. Oil temperature is then sensed by an oil temperature sensor, and the oil temperature is displayed on the OIL TEMP gauge. Oil pressure is sensed by a pressure transmitter, and oil pressure is displayed on the OIL PRESS gauge. If oil pressure drops below normal, a pressure switch is actuated and the OIL PRESS LOW annunciator light and the MASTER CAUTION light illuminate to indicate a low pressure condition.
Engine Fuel System
Fuel pressure into the engine is monitored by an inlet pressure switch. When the inlet pressure is too low the INLET FUEL PRESS annunciator light and MASTER CAUTION light illuminate. Fuel from the fuel supply system passes through the engine driven first stage centrifugal pump.
From the pump, fuel flows through the air / fuel heat exchanger. Bleed air (13th stage) is supplied to the air / fuel heat exchanger through a shutoff valve. The shutoff valve is controlled by a FUEL HEAT switch and timer. When the FUEL HEAT switch is placed to ON (momentary), the valve will open, and bleed air is supplied to the air / fuel heat exchanger for one minute. After one minute, the timer automatically closes the shutoff valve. The FUEL HEAT ON annunciator light illuminates when the valve is open and extinguishes when the valve is closed. Fuel heat is used to prevent or remove ice on the fuel filter. Fuel temperature is sensed downstream from the air / fuel heat exchanger, and temperature is displayed on the FUEL TEMP gauge.
Fuel is filtered before entering the fuel control. If the differential pressure switch senses clogging at the filter, the FUEL FILTER PRESS DROP annunciator light and MASTER CAUTION light illuminate. A bypass valve allows fuel to bypass a clogged filter.
Fuel flow is shut off at the fuel control unit until the FUEL lever is moved out of the OFF position. An engine driven second stage high pressure gear pump pressurizes fuel prior to entering the fuel control unit. The fuel flow transmitter measure fuel delivered to the engine from the fuel control. Fuel flow is displayed on the FUEL FLOW gauge. Heat from engine oil is transferred to the fuel through the fuel / oil heat exchanger.
Thrust Reversers
The thrust reversers are used on the ground only. The reversers are hydraulically powered, target type, and actuation time is approximately 2 seconds. The thrust reverser on each engine consists of two doors (deflectors), which form the aft nacelle fairing when stowed. The door linkage system overcenters to provide positive locking in the stowed position. When extended, the doors direct exhaust gases over and under the nacelle. To prevent accidental extension, separate hydraulically actuated latches prevent the reversers from moving out of the stowed position until the thrust reverser lever is moved toward the reverse thrust position.
As the thrust reverser unlatches, a latch switch turns on an ENG REVERSE UNLOCK light on the center instrument panel. When the reversers are extended, a reverse extended switch turns on an ENG REVERSE THRUST light, also on the center instrument panel.
On the ground, each reverser system receives hydraulic pressure from the respective hydraulic system. Inflight, the hydraulic system is isolated from the reverser system. Each reverser system is equipped with an accumulator, which keeps the reverser locked in flight, and provides energy for one extend actuation after landing. A L or R REVERSER ACCUMULATOR LOW light illuminates if the associated reverser accumulator pressure is below normal.
Continental
Rev. 12/01/00 #29 Flight Manual
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MD-80 Flight Manual 麦道80飞行手册 2(189)
