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 a through 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 single stage 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 Thrust Levers. 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 each engine. 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 the desired 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 PMC automatically maintains that thrust throughout the climb with no further thrust lever adjustments. If the thrust lever is repositioned, the PMC maintains the setting corresponding to the new thrust lever angle. ¡ The PMC includes failure detection and annunciation modules which detect PMC failures and provide a signal to the crew. For detectable failure conditions, the PMC schedules a slow N1 drift over approximately 30 seconds and then illuminates the PMC INOP Light, the ENG System Annunciator and 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. The PMC INOP Light is suppressed below starter cutout engine speed (46% N2). Copyright Smartcockpit.com Ludovic ANDRE / version 00 Smartcockpit.com BOEING 737 SYSTEMS REVIEW Page 2 737 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. As temperature and airspeed decrease, high idle speed also decreases. The average high idle setting is approximately 32% N1. ¡ Engine idle speed is reduced to low idle, approximately 22% N1, four seconds after touchdown. This delay 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 operating channel 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 can operate in Normal or Alternate mode. ¡ The EEC also provides N1 and N2 redline exceedance protection in both Normal and Alternate modes 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 N1 values. The EEC compares commanded N1 to actual N1 and adjusts fuel flow until actual N1 equals commanded N1. ¡ Full rated take-off thrust is available at a thrust lever position less than the forward stop. If the thrust lever is advanced to the forward stop, the EEC limits thrust to the maximum certified thrust ratings for current 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 to the soft alternate mode. When this occurs, the ALTN switch illuminates and the ON indication remains visible. In the soft alternate mode, the EEC uses the last valid flight conditions to define engine 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 the thrust 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 thrust lever position. The maximum certified thrust rating can be exceeded. If the hard alternate mode is entered 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 ON indication is blanked. Copyright Smartcockpit.com Ludovic ANDRE / version 00 Smartcockpit.com BOEING 737 SYSTEMS REVIEW Page 3 737-800 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 most phases of flight. ¡ Approach idle is selected in flight if flaps are in landing configuration or engine anti-ice is ON for either engine. Approach idle provides a higher % RPM than flight minimum idle improving engine acceleration time in the event of a go-around. Approach idle is maintained until TBD-seconds after touchdown, 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 active below FL 150. 2. ENGINE FUEL SYSTEM B737 CLASSICS ¡ Fuel leaves the fuel tank and enters through the Engine Fuel Shutoff Valve, located at the engine mounting wing station. The Engine Fuel Shutoff Valve is electrically controlled by the Engine Start Lever and the Engine Fire Warning Switch. When the engine fuel shutoff valve is closed, the FUEL VALVE 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 a filter. Provisions are made to bypass the 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 Main Engine Control (MEC). As the fuel leaves the second stage fuel pump, a portion of the fuel is diverted to operate the MEC. This fuel is filtered again and then routed through the fuel heater a second time. The fuel heater uses engine oil to heat the fuel for anti-icing purposes. ¡ The MEC, in conjunction with the Power Management Control (PMC), uses thrust lever angle, fan inlet 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 valve is mechanically controlled by the Engine Start Lever. A fuel flow transmitter measures the rate of fuel flow from the MEC. 737 NG ¡ Fuel leaves the fuel tank and enters through the Spar Fuel Shutoff Valve. The Spar Fuel Shutoff Valve is electrically controlled by the Engine Start Lever and the Engine Fire Warning Switch. When the Spar Fuel Shutoff Valve is closed, the SPAR VALVE CLOSED light located on the forward overhead panel illuminates dim. Copyright Smartcockpit.com Ludovic ANDRE / version 00 Smartcockpit.com BOEING 737 SYSTEMS REVIEW Page 4 ¡ Fuel from the first stage fuel pump passes through two heat exchangers where the fuel is heated by IDG oil and engine oil. Fuel then flows through a filter. Provisions are made to bypass the main engine 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 calculate the correct amount of fuel. The EEC sends electric commands to the HMU. The HMU controls the fuel flow. Fuel flows from the HMU through the Engine Fuel Shutoff Valve. The Engine Fuel Shutoff Valve is controlled electrically by the engine start lever and the Engine Fire Warning Switch. When the Engine Fuel Shutoff Valve is closed. The ENG VALVE CLOSED light located on the forward overhead panel, illuminates dim. A fuel 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 and accessory 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, passes through an oil filter, and continues to the engine bearings and gearbox. Sensors for the Oil Pressure Indicator and the LOW OIL PRESSURE warning are located downstream of the oil filter, prior to engine 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 OIL FILTER BYPASS warning illuminates. The oil then passes through the fuel/oil heat exchanger where it is cooled by engine fuel to maintain proper oil temperature prior to returning to the tank. Oil temperature is displayed on the Oil Temperature Indicator and is measured B737 Classics in the scavenge 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 engine crossbreed. The Engine Start Switch GRD position uses DC power from the battery bus to open the starter 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 drive gear system. When the Engine Start Lever is advanced to the IDLE position, fuel is supplied to the combustor where the fuel ignites. ¡ At cutout speed (B737 Classics 46% N2 RPM; B737 NG 56% N2 RPM), power is interrupted to the start switch holding solenoid, allowing the Engine Start Switch to return to the OFF position and the starter valve to close. ¡ During an engine shutdown, the start switch holding-solenoid is held in the cutout position until engine speed falls below 30% N2 RPM. The starter should not be re-engaged until engine speed has decreased below 20% N2 RPM. Copyright Smartcockpit.com Ludovic ANDRE / version 00 Smartcockpit.com BOEING 737 SYSTEMS REVIEW Page 5 5. IGNITION SYSTEM ¡ Two high energy AC systems are provided. The ignitors can only be energized when the Engine Start Lever is in the IDLE position. With the Engine Start Switch in the GRD position, the starter valve opens 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. The Ignition 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 start limit 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, the white box surrounding the EGT digital readout flashes. The flashing white box resets when the start lever 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 the display returns to white when EGT drops below the start limit. Following engine shutdown, the EGT box 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 is detected, the EEC turns off the ignition and shuts off fuel to engine 15 seconds after the start lever is moved to IDLE. 737 NG Auto Relight ¡ An auto-relight capability is provided for flameout protection. Whenever the EEC detects an engine flameout 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 right translating sleeves. Aft movement of the reverser sleeves causes blocker doors to deflect fan discharge 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 from hydraulic 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 system is used, the affected thrust reverser will deploy and retract at a slower rate and some thrust asymmetry can be anticipated. Copyright Smartcockpit.com Ludovic ANDRE / version 00 Smartcockpit.com BOEING 737 SYSTEMS REVIEW Page 6 ¡ The thrust reverser can be deployed when either radio altimeter senses less than 1 0 feet altitude, or when the air/ground sensor is in the ground mode. Movement of the Reverse Thrust Levers is mechanically restricted until the Forward Thrust Levers are in the idle position. When reverse thrust is selected, 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 mechanism restricts further movement of the Reverse Thrust Lever until the reverser sleeves have approached the deployed position. The movement of the Reverse Thrust Levers into reverse thrust engages locking pawls which prevent the Forward Thrust Levers from moving. Terminating reverse thrust removes the locking pawls and restores forward thrust lever movement ability. ¡ When either reverser sleeve moves from the stowed and locked position, the 737 Classics REVERSER UNLOCKED Light, located on the center instrument panel, illuminates; 737 NG amber REV 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 allowing hydraulic pressure to stow and lock the reverser sleeves. After the thrust reverser is stowed, the isolation valve closes. ¡ The REVERSER Light, located on the aft overhead panel, illuminates when the thrust reverser is commanded to stow and extinguishes 1 0 seconds later when the isolation valve closes. Anytime the REVERSER Light illuminates for more than approximately 12 seconds, a malfunction has occurred and the MASTER CAUTION and ENG System Annunciator Light illuminate. ¡ When the reverser sleeves are in the stowed position, a locking actuator inhibits motion of each reverser sleeve until reverser extension is selected. Additionally, an auto-restow circuit compares the actual reverser sleeve position and the command reverser position. In the event of incomplete stowage or uncommanded movement of the reverser sleeves toward the deployed position, the autorestow circuit will open the isolation valve and command the control valve to the stow position directing 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 in the stowed position until the thrust reverser is deployed or until corrective maintenance action is taken. WARNING: Actuation of the thrust reversers on the ground without suitable precautions is dangerous to ground personnel. 7. AIR BLEED SYSTEM COMPRESSOR SECTION ¡ The N1 compressor, or booster section, produces low pressure air and delivers it to the N2 compressor which produces high pressure air. The single stage fan, which is an extension of the first stage of compression, produces very large volumes of bypass air. Each compressor section is driven by its own separate turbine at its own best speed. The high pressure compressor (N2) is governed by the MEC (B737 Classics) or HMU (737 NG) while the fan and low pressure compressor (N1) is driven by its turbine and is free to select the best speed to ensure optimum airflow. This airflow matching feature allows the compressor sections to adjust themselves automatically throughout the operating range of the engine. Copyright Smartcockpit.com Ludovic ANDRE / version 00 Smartcockpit.com BOEING 737 SYSTEMS REVIEW Page 7 FAN BYPASS / BLEED AIR Fan bypass air is used for thrust reversal, generator drive and generator cooling. Fifth stage bleed air is used 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 levers IN IDLE : - 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 start valve 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 Copyright Smartcockpit.com Ludovic ANDRE / version 00 Smartcockpit.com Page 8 BOEING 737 SYSTEMS REVIEW 9. FAULTS & INDICATIONS VALID FOR LIGHT ENGINE CONTROL LOW IDLE LOW OIL PRESSURE LOW OIL PRESSURE OIL FILTER BYPASS OIL FILTER BYPASS ON INOP ON ALTN INDICATION 400 500 ENGINE CONTROL LIGHT (amber) ILLUMINATED : - There is a fault in the engine control system Light operates when engine is operating, aircraft on Ground, < 80 kt prior to takeoff, approximately 30 sec after touchdown LOW IDLE LIGHT (amber) ILLUMINATED : - The thrust lever for either engine is near idle and the MEC on either engine is not commanded to maintain 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) > EICAS ILLUMINATED : - Indicates engine oil pressure is at or below the red radial (13 psi). OIL FILTER BYPASS LIGHT (amber) ILLUMINATED : - Indicates an impending or actual bypass of the scavenge oil filter. 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 POWER MANAGEMENT SWITCH (white) - ON (in view) : Indicates normal control is selected & engine ratings calculated by EEC from sensed atmospheric 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 600 700 800 900 X X X X X X X X X X X X X OIL FILTER BYPASS ALERT (amber) > EICAS ILLUMINATED : - Indicates an impending or actual bypass of the scavenge oil filter. Copyright Smartcockpit.com Ludovic ANDRE / version 00 300 X Smartcockpit.com REVERSER REVERSER UNLOCKED START VALVE OPEN START VALVE OPEN REVERSER LIGHT (amber) ILLUMINATED : - Indicates the thrust reverser is unlocked REVERSER UNLOCKED LIGHT (amber) ILLUMINATED : - Indicates the thrust reverser is unlocked 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 the Starter 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. Copyright Smartcockpit.com Ludovic ANDRE / version 00 Page 9 BOEING 737 SYSTEMS REVIEW X X X X X X Smartcockpit.com BOEING 737 SYSTEMS REVIEW Copyright Smartcockpit.com Ludovic ANDRE / version 00 Page 10 Smartcockpit.com BOEING 737 SYSTEMS REVIEW ENGINE FUEL & OIL SYSTEM - SCHEMATIC B737 CLASSICS Copyright Smartcockpit.com Ludovic ANDRE / version 00 Page 11 Smartcockpit.com BOEING 737 SYSTEMS REVIEW ENGINE FUEL & OIL SYSTEM - SCHEMATIC B737 NG Copyright Smartcockpit.com Ludovic ANDRE / version 00 Page 12 Smartcockpit.com BOEING 737 SYSTEMS REVIEW ENGINE START & IGNITION SYSTEM - SCHEMATIC B737 CLASSICS Copyright Smartcockpit.com Ludovic ANDRE / version 00 Page 13 Smartcockpit.com BOEING 737 SYSTEMS REVIEW ENGINE START & IGNITION SYSTEM - SCHEMATIC B737 NG Copyright Smartcockpit.com Ludovic ANDRE / version 00 Page 14 Smartcockpit.com BOEING 737 SYSTEMS REVIEW Copyright Smartcockpit.com Ludovic ANDRE / version 00 Page 15 Smartcockpit.com BOEING 737 SYSTEMS REVIEW FAN BYPASS / BLEED AIR Copyright Smartcockpit.com Ludovic ANDRE / version 00 Page 16