B737-Powerplant Systems Summary

7/27/2019 B737-Powerplant Systems Summary

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CopyrightSmartcockpit.comLudovic ANDRE / version 00

Smartcockpit.com BOEING 737 SYSTEMS REVIEW Page 1

POWERPLANT

1. GENERAL

The aircraft is powered by two CFM International high bypass ratio turbofan engines.

The engine is a dual rotor assembly consisting of a fan rotor (N1) and a compressor rotor (N2).

The N1 rotor consists of a single stage fan and a three stage booster section connected by athrough shaft to a four stage low pressure turbine.

The N2 rotor is a nine stage axial flow compressor connected by a through shaft to a singlestage high pressure turbine. The first four stages of the compressor are variable.

Fan air and combustion gasses exit through separate nozzles at the rear of the engine.

737 Classics PMC The Main Engine Control (MEC) schedules fuel to provide the thrust called for by the Thrust Lever

setting. This fuel flow is further refined electronically by the Power Management Control (PMC)without moving the Thrust Levers.

737 NG FADEC The Full Authority Digital Electronic Control (FADEC) schedules fuel to provide the thrust called for by

the Thrust Lever setting. The FADEC can adjust the fuel flow without moving the Forward ThrustLevers.

Reverser A sliding sleeve, fixed vane thrust reverser system is installed which redirects bypass fan air to aid in

stopping the aircraft.

2.MAIN COMPONENTS & SUBSYSTEMS

737 CLASSICS POWER MANAGEMENT CONTROL

The thrust control system consists of a hydromechanical MEC unit and a PMC unit mounted on eachengine. The PMC is an electronic system with limited authority over the MEC. The PMC uses MEC

thrust lever angle, N1 speed, inlet temperature and pressure to adjust, or trim, the MEC to obtain thedesired N1 speed. The PMC adjusts fuel flow as a function of thrust lever angle.

The PMC provides a constant thrust climb feature. When thrust is set for the climb, the PMCautomatically maintains that thrust throughout the climb with no further thrust lever adjustments. Ifthe thrust lever is repositioned, the PMC maintains the setting corresponding to the new thrust leverangle.

The PMC includes failure detection and annunciation modules which detect PMC failures and providea signal to the crew. For detectable failure conditions, the PMC schedules a slow N1 drift overapproximately 30 seconds and then illuminates the PMC INOP Light, the ENG System Annunciatorand the MASTER CAUTION Lights. For a PMC failure, the PMC can be selected OFF by a P/B on

the aft overhead panel. The engine speed is then controlled by the hydromechanical MEC only. ThePMC INOP Light is suppressed below starter cutout engine speed (46% N2).


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737 CLASSICS IDLE RPM

There are two engine idle speeds, low idle and high idle.

The minimum engine speed for all flight phases is high idle, which varies with flight conditions. Astemperature and airspeed decrease, high idle speed also decreases. The average high idle setting isapproximately 32% N1.

Engine idle speed is reduced to low idle, approximately 22% N1, four seconds after touchdown. Thisdelay is provided to enhance engine speed acceleration for reverse thrust.

737 NG FADEC

The FADEC consist of an Electronic Engine Control (EEC) and a Hydraulic Mechanical Unit (HMU).The EEC has two independent control channels and automatically switches channel if the operatingchannel fails. With each engine start or start attempt, the EEC alternates between control channels.The EEC receives thrust lever inputs to automatically control forward and reverse thrust and canoperate in Normal or Alternate mode.

The EEC also provides N1 and N2 redline exceedance protection in both Normal and Alternatemodes but does not provide EGT redline exceedance protection.

EEC NORMAL MODE

In the normal mode, the EEC uses sensed flight conditions and bleed air demand to calculate N1values. The EEC compares commanded N1 to actual N1 and adjusts fuel flow until actual N1 equalscommanded N1.

Full rated take-off thrust is available at a thrust lever position less than the forward stop. If the thrustlever is advanced to the forward stop, the EEC limits thrust to the maximum certified thrust ratings forcurrent conditions.

EEC ALTERNATE MODE

The EEC can operate in either of two alternate modes, soft or hard.

If required signals are not available to operate in the normal mode, the EEC automatically changes tothe soft alternate mode. When this occurs, the ALTN switch illuminates and the ON indicationremains visible. In the soft alternate mode, the EEC uses the last valid flight conditions to defineengine parameters. Thrust rating shortfalls or exceedances may occur as flight conditions change.The soft alternate mode remains active until the hard alternate mode is entered by either retarding thethrust lever to idle or by manually selecting ALTN with the EEC switch on the aft overhead panel.

When the hard alternate mode is entered, the EEC reverts to the alternate mode thrust schedule.Hard alternate mode thrust is always equal to or greater than normal mode thrust for the same thrustlever position. The maximum certified thrust rating can be exceeded. If the hard alternate mode isentered by reducing the thrust lever to idle while in the soft alternate mode, the ALTN switch remains

illuminated and the ON indication remains visible. When ALTN is selected manually, the ONindication is blanked.


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737-800 IDLE RPM

The EEC automatically selects ground minimum idle, flight minimum idle and approach idle.

Ground minimum idle is selected for ground operations and flight minimum idle is selected for mostphases of flight.

Approach idle is selected in flight if flaps are in landing configuration or engine anti-ice is ON for eitherengine. Approach idle provides a higher % RPM than flight minimum idle improving engineacceleration time in the event of a go-around. Approach idle is maintained until TBD-seconds aftertouchdown, when engine idle speed is reduced to ground minimum idle.

In flight, if a fault prevents the EEC from receiving flap or anti-ice signals, approach idle is activebelow FL 150.

2. ENGINE FUEL SYSTEM

B737 CLASSICS

Fuel leaves the fuel tank and enters through the Engine Fuel Shutoff Valve, located at the enginemounting wing station. The Engine Fuel Shutoff Valve is electrically controlled by the Engine StartLever and the Engine Fire Warning Switch. When the engine fuel shutoff valve is closed, the FUELVALVE CLOSED Light located on the forward overhead panel illuminates dim.

Fuel passes from the first stage of the engine driven fuel pump through a fuel/oil heat exchanger to afilter. Provisions are made to bypass the heat exchanger or the filter in the event of failure orblockage. Illumination of the FILTER BYPASS Light indicates an impending or actual bypass of thefuel filter due to contamination.

The second stage fuel pump provides high pressure fuel to the Main Engine Control (MEC). As thefuel leaves the second stage fuel pump, a portion of the fuel is diverted to operate the MEC. This fuelis filtered again and then routed through the fuel heater a second time. The fuel heater uses engineoil to heat the fuel for anti-icing purposes.

The MEC, in conjunction with the Power Management Control (PMC), uses thrust lever angle, faninlet pressure and temperature, N1 RPM and N2 RPM to meter the correct amount of fuel to the

combustor. Fuel flows from the MEC through the MEC fuel shutoff valve. The MEC fuel shutoff valveis mechanically controlled by the Engine Start Lever. A fuel flow transmitter measures the rate of fuelflow from the MEC.

737 NG

Fuel leaves the fuel tank and enters through the Spar Fuel Shutoff Valve. The Spar Fuel ShutoffValve is electrically controlled by the Engine Start Lever and the Engine Fire Warning Switch. Whenthe Spar Fuel Shutoff Valve is closed, the SPAR VALVE CLOSED light located on the forwardoverhead panel illuminates dim.


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Fuel from the first stage fuel pump passes through two heat exchangers where the fuel is heated byIDG oil and engine oil. Fuel then flows through a filter. Provisions are made to bypass the mainengine oil heat exchanger or the filter in the event of failure or blockage. Illumination of the FILTER

BYPASS Light indicates an impending or actual bypass of the fuel filter due to contamination.

The second stage fuel pump provides high pressure fuel to the Hydraulic Mechanical Unit (HMU).Excess fuel from the HMU is directed back to the main engine oil cooler.

The EEC uses thrust lever angle, fan inlet pressure and temperature, N1 and N2 RPM to calculatethe correct amount of fuel. The EEC sends electric commands to the HMU. The HMU controls thefuel flow. Fuel flows from the HMU through the Engine Fuel Shutoff Valve. The Engine Fuel ShutoffValve is controlled electrically by the engine start lever and the Engine Fire Warning Switch. Whenthe Engine Fuel Shutoff Valve is closed. The ENG VALVE CLOSED light located on the forwardoverhead panel, illuminates dim. Afuel flow transmitter measures the rate of fuel flow from the HMU.

3. ENGINE OIL SYSTEM

Oil from the engine oil tank is circulated through the engine to lubricate the engine bearings andaccessory gearbox. Oil quantity is displayed on the Oil Quantity Indicator.

The oil system is pressurized by the engine driven oil pump. The oil leaves the oil pump, passesthrough an oil filter, and continues to the engine bearings and gearbox. Sensors for the Oil PressureIndicator and the LOW OIL PRESSURE warning are located downstream of the oil filter, prior toengine lubrication. The oil is returned to the oil tank by means of engine driven scavenge pumps.From the scavenge pumps the oil passes through a scavenge filter. Should the filter become

contaminated, oil automatically bypasses the filter. Prior to the oil bypassing the filter, the OILFILTER BYPASS warning illuminates. The oil then passes through the fuel/oil heat exchanger whereit is cooled by engine fuel to maintain proper oil temperature prior to returning to the tank. Oiltemperature is displayed on the Oil Temperature Indicator and is measured B737 Classics in thescavenge line; B737 NG in the supply line.

4. ENGINE START SYSTEM

The engines may be started with air from the APU, from a ground source, or by using enginecrossbreed. The Engine Start Switch GRD position uses DC power from the battery bus to open thestarter valve and allow pressure from the pneumatic manifold to rotate the starter.

When the starter valve is not closed, the amber START VALVE OPEN indication illuminates.

The starter is a turbine-type air motor which rotates the N2 compressor through the accessory drivegear system. When the Engine Start Lever is advanced to the IDLE position, fuel is supplied to thecombustor where the fuel ignites.

At cutout speed (B737 Classics 46% N2 RPM; B737 NG 56% N2 RPM), power is interrupted to thestart switch holding solenoid, allowing the Engine Start Switch to return to the OFF position and thestarter valve to close.

During an engine shutdown, the start switch holding-solenoid is held in the cutout position untilengine speed falls below 30% N2 RPM. The starter should not be re-engaged until engine speed hasdecreased below 20% N2 RPM.


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5. IGNITION SYSTEM

Two high energy AC systems are provided. The ignitors can only be energized when the EngineStart Lever is in the IDLE position. With the Engine Start Switch in the GRD position, the starter valveopens and the selected igniter(s) are energized.

The CONT position energizes the selected igniter(s).

The FLT position energizes both igniters.

The Ignition Select Switch selects either the LEFT, RIGHT or BOTH igniters for both engines. TheIgnition Select Switch is bypassed when the Engine Start Switch is in FLT.

IGN L, powered by the AC transfer bus, provides single high energy ignition to the left igniter.

IGN R, powered by the AC standby bus, provides single high energy ignition to the right igniter.

737 NG ABNORMAL START PROTECTION

During ground starts, the EEC monitors engine parameters to detect impending hot starts, EGT startlimit exceedances, and wet starts. These protection features do not function during inflight starts.

If an impending hot start is detected by a rapid rise in EGT or EGT approaching the start limit, thewhite box surrounding the EGT digital readout flashes. The flashing white box resets when the startlever is moved to CUTOFF or the engine reaches idle N2.

If the EGT exceeds the starting limit, the EGT display, both box and dial, turn red. The EEC

automatically turns off the ignition and shuts off fuel to the engine. The alert terminates and thedisplay returns to white when EGT drops below the start limit. Following engine shutdown, the EGTbox turns red to remind the crew of the exceedance.

A wet start occurs if the EGT does not rise after the start lever is moved to IDLE. If a wet start isdetected, the EEC turns off the ignition and shuts off fuel to engine 15 seconds after the start lever ismoved to IDLE.

737 NG Auto Relight

An auto-relight capability is provided for flameout protection. Whenever the EEC detects an engineflameout with the ENGINE START switches in OFF, both ignitors are activated. A flameout is

detected when an uncommanded rapid decrease in N2 occurs or N2 is between 57% and 50%.

6. THRUST REVERSER

Each engine is equipped with a hydraulically operated thrust reverser, consisting of left and righttranslating sleeves. Aft movement of the reverser sleeves causes blocker doors to deflect fandischarge air forward, through fixed cascade vanes, producing reverse thrust.

Hydraulic pressure for the operation of engine No. 1 and engine No. 2 thrust reversers comes fromhydraulic systems A and B, respectively. If hydraulic system A or B fails, alternate operation for the

affected thrust reverser is available through the standby hydraulic system. When the standby systemis used, the affected thrust reverser will deploy and retract at a slower rate and some thrustasymmetry can be anticipated.


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The thrust reverser can be deployed when either radio altimeter senses less than 1 0 feet altitude, orwhen the air/ground sensor is in the ground mode. Movement of the Reverse Thrust Levers ismechanically restricted until the Forward Thrust Levers are in the idle position. When reverse thrust isselected, the isolation valve opens and the thrust reverser control valve moves to the deploy position,

allowing hydraulic pressure to unlock and deploy the reverse sleeves. An interlock mechanismrestricts further movement of the Reverse Thrust Lever until the reverser sleeves have approachedthe deployed position. The movement of the Reverse Thrust Levers into reverse thrust engageslocking pawls which prevent the Forward Thrust Levers from moving. Terminating reverse thrustremoves the locking pawls and restores forward thrust lever movement ability.

When either reverser sleeve moves from the stowed and locked position, the 737 ClassicsREVERSER UNLOCKED Light, located on the center instrument panel, illuminates; 737 NG amberREV indication on the upper DU is displayed. As the thrust reverser reaches the deployed position,the Reverse Thrust Lever can be raised to detent No. 2 and 737 NG the REV indication turns green.This position provides adequate reverse thrust for normal operations. When necessary, the Reverse

Thrust Lever can be pulled beyond detent No. 2, providing maximum reverse thrust.

Downward motion of the Reverse Thrust Lever past detent No. 1 will command the reverser to stow.Once the thrust reverser is commanded closed, the control valve moves to the stow position allowinghydraulic pressure to stow and lock the reverser sleeves. After the thrust reverser is stowed, theisolation valve closes.

The REVERSER Light, located on the aft overhead panel, illuminates when the thrust reverser iscommanded to stow and extinguishes 1 0 seconds later when the isolation valve closes. Anytime theREVERSER Light illuminates for more than approximately 12 seconds, a malfunction has occurredand the MASTER CAUTION and ENG System Annunciator Light illuminate.

When the reverser sleeves are in the stowed position, a locking actuator inhibits motion of eachreverser sleeve until reverser extension is selected. Additionally, an auto-restow circuit compares theactual reverser sleeve position and the command reverser position. In the event of incompletestowage or uncommanded movement of the reverser sleeves toward the deployed position, the auto-restow circuit will open the isolation valve and command the control valve to the stow positiondirecting hydraulic pressure to stow the reverser sleeves. Once the auto-restow circuit is activated,the REVERSER light will illuminate, the isolation valve remains open and the control valve is held inthe stowed position until the thrust reverser is deployed or until corrective maintenance action istaken.

WARNING: Actuation of the thrust reversers on the ground without suitable precautions is dangerousto ground personnel.

7. AIR BLEED SYSTEM

COMPRESSOR SECTION

The N1 compressor, or booster section, produces low pressure air and delivers it to the N2compressor which produces high pressure air. The single stage fan, which is an extension of the firststage of compression, produces very large volumes of bypass air. Each compressor section is drivenby its own separate turbine at its own best speed. The high pressure compressor (N2) is governedby the MEC (B737 Classics) or HMU (737 NG) while the fan and low pressure compressor (N1) isdriven by its turbine and is free to select the best speed to ensure optimum airflow. This airflowmatching feature allows the compressor sections to adjust themselves automatically throughout theoperating range of the engine.


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FAN BYPASS / BLEED AIR

Fan bypass air is used for thrust reversal, generator drive and generator cooling. Fifth stage bleed air isused for the Pneumatic and Engine Anti-ice systems. However, at low thrust settings, fifth stage air

pressure is inadequate, so ninth stage bleed air is used instead.

8. CONTROLS & INDICATORS

Engine start leversINIDLE :- energizes the ignition system- B737 Classics : Electrically opens engine fuel shutoff valve & mechanically opens the Main Engine

Control (MEC) shutoff valve.- B737 NG : enables the EEC to open the spar fuel valve & the engine fuel shutoff valve.

CUTOFF :- B737 Classics : closes the engine fuel shutoff valve in the wing & the MEC shutoff valve.- B737 Classics : Ignition system is de-energized- B737 NG : commands the EEC to close the spar fuel valve & the engine fuel shutoff valve.

Engine start switch

GRD (solenoid held, spring-loaded to OFF) :- opens the starter valve- provides high energy ignition when the Engine Start Lever is moved from CUTOFF to IDLE

B737 Classics & B737 NG ground start : the selected igniter(s) is energized & solenoid of the startvalve is held to 46 % N2 (B737 Classics) & 56 % N2 (B737 NG)

B737 NG air start : both igniters are energized

OFF :- No ignition- B737 NG Automatic ignition operates both igniters when engine start lever is in IDLE and :

an uncommanded rapid engine (N2) decrease or,

N2 is between 57 % & 50 % or,

In flight N2 is between idle & 5 %

CONT :- Energizes the selected igniter(s) with the Engine Start Lever in IDLE (used during takeoff, landing &

Engine anti-ice ops)- B737 NG provides (in flight) ignition to both igniters when N2 is < idle & engine start lever is in IDLE

FLT :- Energizes both igniters when the Engine Start Lever is in IDLE- The Ignition Select Switch is bypassed when the Engine Start Switch is in FLT


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9. FAULTS & INDICATIONS

VALID FORLIGHT INDICATION 300 400 500 600 700 800

900

ENGINE CONTROL LIGHT (amber)ILLUMINATED :- There is a fault in the engine control systemLight operates when engine is operating, aircraft onGround, < 80 kt prior to takeoff, approximately 30 secafter touchdown

X X X

LOW IDLE LIGHT (amber)ILLUMINATED :- The thrust lever for either engine is near idle and

the MEC on either engine is not commanded tomaintain high idle RPM inflight

- The speed of either engine is below 25 % N1 inflight

X X X

LOW OIL PRESSURE LIGHT (amber)ILLUMINATED :- Indicates engine oil pressure is at or below the red

radial (13 psi).

X X X

LOW OIL PRESSURE ALERT (amber) > EICASILLUMINATED :- Indicates engine oil pressure is at or below the red

radial (13 psi).

X X X

OIL FILTER BYPASS LIGHT (amber)ILLUMINATED :

- Indicates an impending or actual bypass of thescavenge oil filter.

X X X

OIL FILTER BYPASS ALERT (amber) > EICASILLUMINATED :- Indicates an impending or actual bypass of the

scavenge oil filter.

X X X

POWER MANAGEMENT SWITCH (white)- ON (in view) : Indicates the PMC is selected ON- INOP (in view) : indicates the PMC is INOP when

engine speed is > 46% N2

X X X

POWER MANAGEMENT SWITCH (white)- ON (in view) : Indicates normal control is selected &

engine ratings calculated by EEC from sensedatmospheric conditions & bleed air demand.

- ON (blanked)switches have been manually operated- ALTN (in view) : indicates EEC has automatically

switches to alternate control or it has been selected

manually + EEC provides rated thrust or higher

Note : Both ON & ALTN may be in view if EEC has

automatically switched to soft alternate mode. EGT

limits must be observed in both normal & alternate

control modes.

X X X

LOW

IDLE

OIL FILTER

BYPASS

LOW OIL

PRESSURE

OIL FILTER

BYPASS

LOW OIL

PRESSURE

ON

INOP

ON

ALTN

ENGINE

CONTROL


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REVERSER LIGHT (amber) ILLUMINATED :

- Indicates the thrust reverser is unlocked

REVERSER UNLOCKED LIGHT (amber)

ILLUMINATED :- Indicates the thrust reverser is unlocked

X X X X X X

START VALVE OPEN LIGHT (amber)

ILLUMINATED :

- Indicates the engine starter valve is open & air is

being supplied to the starter

X X X

START VALVE OPEN ALERT (amber) > EICAS

ILLUMINATED :

- Indicates the engine starter valve is open & air is

being supplied to the starter

Note : in case of uncommanded opening of theStarter valve, low oil pressure or oil filter bypass

(actual or impending), the associated alert flashes

for 10 seconds & solid amber boxes are displayed

flashing in the other two positions. After 10 seconds,

only the alert remains steady.

Flashing is inhibited :

- During takeoff between 80 kt & 400 ft RA, or 30 sec.

after reaching 80 kt (whichever comes first)

- During landing between 200 ft RA until 30 sec.

after touchdown

If flashing is inhibited, an alert illuminates steady

only.

X X X

REVERSER

UNLOCKED

START VALVE

OPEN

START VALVE

OPEN

REVERSER


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ENGINE FUEL & OIL SYSTEM- SCHEMATIC B737 NG


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ENGINE START & IGNITIONSYSTEM

- SCHEMATIC B737 CLASSICS


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ENGINE START & IGNITIONSYSTEM

- SCHEMATIC B737 NG


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FAN BYPASS / BLEED AIR

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B737-Powerplant Systems Summary

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