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BOEING 737 SYSTEMS REVIEW
Page 1
FLIGHT CONTROLS
1. GENERAL
¡ The primary flight controls, ailerons, elevators and rudders, are hydraulically powered. Hydraulic
power is provided from hydraulic systems A and B; either system can operate all primary flight
controls.
¡ The ailerons and elevators may be operated manually if required. The rudder may be operated by
the standby hydraulic system if system A and/or B pressure is not available.
¡ The ailerons are assisted by flight spoilers for roll control. The spoilers are hydraulically powered
from system A (inboard) and B (outboard) and operate proportionally with aileron movement. The
horizontal stabilizer may be positioned by electric trim, or manually through the trim wheels. During
automatic flight, the autopilot trim controls the stabilizer position.
¡ The Surface Position Indicator (if installed), located on the Captain's instrument panel, or, on 737NG
the system display on the lower Display Unit, displays deflection of the ailerons, rudder and elevators.
Aerodynamic braking is provided in flight by the flight spoilers operating as speedbrakes. On ground,
flight spoilers and ground spoilers are used in combination to destroy lift.
¡ High lift for take-off and landing is provided by trailing edge flaps and leading edge flaps and slats (LE
devices). Normally, these surfaces are extended and retracted by hydraulic system B. Alternatively,
the trailing edge flaps may be extended and retracted electrically. The leading edge devices may be
extended by the standby hydraulic system. No alternate retraction system is provided for the leading
edge devices.
¡ The autoslat system improves handling qualities at high angles of attack during operations with flaps
set at positions 1 through 5. Autoslat operation deploys the slats from intermediate to full extended
position prior to stick shaker activation.
2. MAIN COMPONENTS AND SUBSYSTEMS
ROLL CONTROL
¡ The roll control surfaces consist of hydraulically powered ailerons (assisted by tabs*) and flight
spoilers, which are controlled by rotating either control wheel.
* a tab is an aerodynamic boost which reduces force required to position the aileron in flight.
Ailerons
¡ The ailerons are positioned by the pilot's control wheels, which are linked together by cables to
supply the mechanical input to two separate hydraulic power control units. Hydraulic systems A and
B provide pressure to the power control units to operate the ailerons. The two Flight Control
Switches control hydraulic pressure shutoff valves for each aileron. These same switches also
control hydraulic pressure to the elevator and rudder.
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¡ The right and left ailerons are connected by the cable-drive system. Either hydraulic system is
capable of providing full power control. In the event of total hydraulic power failure (manual
reversion), rotation of the control wheels mechanically positions the ailerons. Manual control forces
required are higher due to frictional and aerodynamic loads.
¡ If the aileron system jams, a transfer mechanism allows the First Officer to bypass the aileron system
and operate the flight spoilers for roll control.
¡ Aileron trim is accomplished by simultaneous operation of the trim switches located on the control
stand. Movement of both trim switches electrically repositions the aileron feel and centering
mechanism and redefines the ailerons neutral position.
¡ If aileron trim is used with the autopilot engaged, the trim is not reflected in the control wheel
position. The autopilot overpowers the trim and holds the control wheel where it is required for
heading/track control. Any aileron trim applied when the autopilot is engaged can result in an out of
trim condition and an abrupt rolling movement when the autopilot is disconnected.
Note : aileron trim needs hydraulic power (no trim in case of manual reversion)
Spoilers
¡ Two (737 Classics) respectively four (737NG) flight spoilers are located on the upper surface of each
wing. The spoilers are powered by hydraulic system A and hydraulic system B. Hydraulic pressure
shutoff valves are controlled by the two Flight Spoiler Switches.
¡ The flight spoilers are hydraulically actuated in response to movement of the aileron controls (spoiler
range starts with control yoke > 10° & max flight spoiler with yoke fully turned). A spoiler mixer,
connected to the aileron cable-drive, controls the hydraulic power control units on each spoiler panel
to provide spoiler movement proportional to aileron movement. The flight spoilers rise on the wing
with up aileron and remain faired on the wing with down aileron.
¡ With Loss oh hydraulics A & B (manual reversion), ailerons have mechanical back-up & spoilers are
INOP.
PITCH CONTROL
¡ The pitch control surfaces consist of hydraulically powered elevators and an electrically powered
stabilizer.
¡ Cables connect the pilot's control columns to elevator Power Control Units (PCUs) which are
powered by hydraulic system A & B (4 inputs : Pilot yoke, autopilot, mach trim & neutral shift)
¡ The stabilizer is normally controlled by either the stabilizer trim switches on the control wheel or the
autopilot.
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BOEING 737 SYSTEMS REVIEW
Page 3
Elevators
¡ The elevators are interconnected by a torque tube and are normally powered by system A and
system B PCUS. Hydraulic pressure to the units is controlled by A and B Flight Control Switches on
the forward overhead panel. Either hydraulic system is capable of full elevator operation.
¡ In the event of failure of both hydraulic systems A and B (manual reversion), the elevators are
controlled manually from either control column. Elevator balance tabs operate continuously during
normal or manual reversion operations.
¡ Elevator feel is provided by the elevator feel computer. Inputs of airspeed (from the elevator pitot
system) and stabilizer position (center of gravity) enable the computer to simulate aerodynamic
forces. Feel is transmitted to the control columns by the elevator feel and centering unit. The feel
computer utilizes system A or B pressure to operate the feel system. Whichever system is providing
higher pressure is the only one utilized by the feel computer.
¡ If either system A or B fails, the computer senses the imbalance, and the FEEL DIFF PRESS Light
illuminates when the flaps are up, The light also illuminates if one of the elevator feel pitot systems
fails or a frozen pitot probe results in a difference in elevator feel computer output pressures. The
feel system operates normally with only one hydraulic system operating.
¡ A Mach trim system provides speed stability at Mach numbers above M. 615. The elevators are
adjusted nose up in a programmed manner with respect to the stabilizer position as speed is
increased to compensate for aft movement of the center of lift at higher Mach. Engagement and
disengagement are accomplished automatically as a function of airspeed.
¡ Mach information received from the Air Data Computer (B737 Classics) or Air Data Inertial
Reference Unit (B737NG), is used by the flight control computers to adjust the control column neutral
position.
¡ A single channel failure causes the MACH TRIM FAIL Light to illuminate upon Master Caution recall
and extinguishing after reset. A dual channel failure would result in a failure or unreliable Mach trim,
indicated by illumination of the MACH TRIM FAIL Light.
Stabilizer
¡ The horizontal stabilizer may be operated by:
- Main electric trim.
- Autopilot trim.
- Stabilizer trim wheel.
¡ Pilot stabilizer trim switches actuate the main electric trim when the aircraft is flown manually.
The switches trip the Autopilot if it is engaged.
¡ The main electric trim has two speed modes:
- High speed with flaps extended.
- Low speed with flaps retracted.
¡ Manual control of the stabilizer is through cables connected to the same mechanism, allowing the
pilot to position the stabilizer manually by the trim wheels. The trim wheels follow automatically when
electric stabilizer trim is actuated, and the Stabilizer Trim Indicator shows the trim unit setting.
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BOEING 737 SYSTEMS REVIEW
Page 4
Examples :
Trim Authority
Main Electric Trim Flaps retracted
Main Electric Trim Flaps extended
Autopilot Trim
Manual Trim
-300
2.5 - 12.5 units
0.25 - 12.5 units
0.25 - 14.0 units
0 - 17.0 units
-400
2.8 - 12.5 units
0.25 - 12.5 units
0.25 - 14.0 units
0 - 17.0 units
-800
3.95 - 14.5 units
0.05 - 14.5 units
0.05 - 14.5 units
-0.20 - 16.9 units
¡ The green band range of the Stabilizer Trim Indicator shows permissible take-off trim range.
An intermittent horn sounds if take-off is attempted with the stabilizer trim not in the green band
range.
¡ Main electric and autopilot trim may be disengaged by cutout switches located on the control stand.
¡ A Control Column actuated Stabilizer Trim Cutout Switch stops operation of the main electric and
autopilot trim when the control column movement opposes trim direction.
¡ A Stab Trim Override Switch, located on the aft electronic panel, bypasses the Control Column
actuated Stabilizer Trim Cutout Switch. When the switch positioned to OVERRIDE, main electric trim
can be used regardless of control column position.
¡ The stabilizer is held in position by a dual brake system. Either stabilizer brake can maintain the
position set by the trim system. In the event of a dual brake failure, and without pilot response,
airloads can drive the stabilizer to its mechanical stops. Main electric trim can resist this motion, but
control column opposition will make the condition worse.
Speed Trim
The speed trim system provides automatic trim inputs during manual flight. The system trims the aircraft
using autopilot trim. It will most frequently be observed in operation during take-off and go-arounds.
Conditions for speed trim operations are listed below:
Flaps not up (737-300 & 500).
Flaps up or down (737-400 & NG).
Airspeed 100-300 KIAS (B737 Classics) or 100 KIAS - M.050 (B737 NG).
10 seconds after lift-off.
5 seconds following release of trim switches.
N1 above 60%.
Autopilot not engaged.
Sensing of trim requirement.
¡ A single channel failure causes the SPEED TRIM FAIL Light to illuminate upon Master Caution recall
and extinguish after reset. A dual channel failure would result in a failure or unreliable speed trim,
indicated by illumination of the SPEED TRIM FAIL Light.
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BOEING 737 SYSTEMS REVIEW
Page 5
YAW CONTROL
Rudder
¡ Hydraulic system A and system B supply the main rudder PCU. Either hydraulic system operates
the rudder if required. Either set of rudder pedals positions the rudder through the rudder PCU.
Rudder feel is provided by a feel and centering unit.
¡ B737NG: With airspeed above 135 kt, hydraulic system A pressure to the rudder PCU is reduced in
order to limit full rudder authority.
¡ Rudder trim is accomplished by operation of the Rudder Trim Control Switch located on the aft
electronic panel. Operation of the Trim Control Switch electrically repositions the rudder feel and
centering mechanism which results in a shift in the rudder neutral position. The rudder pedals are
displaced proportionately.
¡ In the event of a loss of system A and/or system B pressure, the standby hydraulic system furnishes
hydraulic pressure to operate the rudder through a separate PCU.
Rudder Pressure Reducer (Modification to the B737 Classics and fifted to the latest B737 NG)
¡ Reduces max rudder deflection above about 1000 ft RA, resulting in reduced rudder authority
allowing crews more time to respond and recover from unnecessary large rudder deflections
regardless of origin.
¡ Does not change hydraulic flow rate so rudder deflection rate remains unchanged
¡ Requires the installation of a hydraulic pressure reducer in the system A line side of the rudder PCU,
reducing pressure to the rudder to 1 000 psi. No modification of the system B side of the rudder PCU
is carried out
¡ commands reduced pressure when the aircraft climbs through 1000 ft RA on departure, returning to
normal at 700 ft RA on arrival. Above these heights, full pressure to the rudder will be commanded if
any one of the following occurs :
1. Hydraulic system B failure
2. Captain's Radio Altimeter fails
3. Engine failure (looks at greater than 40% N1 split between engines)
4. Loss of electrical power to RPR solenoid
¡ If hydraulic system A fails, normal (3000 psi) hyd system B pressure is still available to the PCU, but,
if the RPR solenoid or associated systems fail to return the hyd system A pressure to the high
setting, hyd system A Flight Control LOW PRESSURE light will illuminate at 700 ft RA, with the
associated MASTER CAUTION, and standby rudder is automatically commanded to operate
Note : this does not produce a crosswind controllability issue
¡ Controllability issue may be of concern if the above scenario were to occur, followed by a
subsequent go-around and engine failure during the missed approach - not enough rudder in theory
- if you go-around after LOW PRESSURE light illuminates at 700 ft RA, after passing 1 000 ft RA,
system logic will extinguish the light
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BOEING 737 SYSTEMS REVIEW
Page 6
¡ Autoland operations are not affected by RPR remaining at low pressure
¡ During preflight, system A Flight Control LOW PRESSURE light may remain on for up to 5 seconds
¡ RPR failure mode designed to fail to normal (high) pressure.
¡ If failure were to occur in high mode, no indication to pilot is as yet available
- maintenance would catch on their check
¡ Modification also requires installation of two channel digital yaw damper with BITE
Yaw Damper B737 Classics
¡ The yaw damper system consists of yaw damper coupler, rate gyro, and a yaw damper actuator in
the rudder PCU.The rate gyro sends yaw change signals to the yaw damper coupler. Command
signals are then sent to the rudder PCU to deflect the rudder. No rudder pedal movement results
from yaw damper operation.
¡ B737-400:Airspeed signals from the Air Data Computer decrease the amount of yaw damper rudder
deflection at higher airspeeds.
¡ The yaw damper uses hydraulic system B pressure only. If hydraulic system B pressure is lost, the
Yaw Damper Switch remains in the ON position until the system B Flight Control Switch is positioned
to OFF or STBY RUD. Then the Yaw Damper Switch disengages, the amber YAW DAMPER light
illuminates and the Yaw Damper Switch cannot be re-engaged.
Yaw Damper B737 NG
¡ The yaw damper system consists of a main and standby yaw damper. Both yaw dampers are
controlled through Stall Management/Yaw Damper (SMYD) computers. SMYD computers provide
yaw damper inputs to the main rudder power control unit (PCU) or standby rudder PCU, as
appropriate.
¡ Airspeed signals from the Air Data Inertial Reference Units decrease the amount of Yaw Damper
rudder deflection at higher airspeeds.
¡ Either yaw damper is capable of providing dutch roll prevention, gust damping and turn co-ordination.
Yaw damper operation does not result in rudder pedal movement. Only main yaw damper inputs are
shown on the yaw damper indicator.
¡ During normal operation the main yaw damper uses hydraulic system B. If hydraulic system B
pressure is lost, the Yaw Damper switch remains in the ON position until the B Flight Control switch
is positioned to OFF or STBY RUD. Then the Yaw Damper switch disengages, the amber YAW
DAMPER light illuminates and the Yaw Damper switch cannot be re-engaged.
¡ During manual reversion flight (loss of hydraulic system A and B pressure), both FLT CONTROL
switches are positioned to STBY RUD. In this case, the YAW DAMPER switch can be reset to ON
and the standby hydraulic system powers the standby yaw damper.
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BOEING 737 SYSTEMS REVIEW
Page 7
SPEEDBRAKES
¡ Speed brakes consist of flight spoilers and ground spoilers. The Speed Brake Lever controls a
spoiler mixer, which positions the flight spoiler PCUs and a ground spoiler control valve.
¡ The surfaces are actuated by hydraulic power supplied to the PCUs or to actuators on each surface.
Ground spoilers operate only on the ground, due to a ground spoiler shutoff valve which remains
closed until the main gear strut compresses on touchdown.
In Flight Operation
¡ Actuation of Speed Brake Lever causes all flight spoiler panels to rise symmetrically to act as speed
brakes.
CAUTION:
The Speed Brake lever can be raised to the UP position inflight. This results in extension of
the flight spoilers to the full up (ground spoiler) position.
Ground Operation
¡ All flight and ground spoilers automatically rise to full extend on landing, if the Speed Brake Lever is
in the ARMED position and both Thrust Levers are in IDLE. When spin-up occurs on any two main
wheels, the Speed Brake Lever moves to the UP position, and the flight spoilers extend. When the
right main landing gear shock strut is compressed, a mechanical linkage opens a hydraulic valve to
extend the ground spoilers.
¡ If a wheel spin-up signal is not detected, the Speed Brake Lever moves to the UP position, and all
spoiler panels deploy automatically after the ground safety sensor engages in the ground mode.
¡ After touchdown, all spoiler panels retract automatically if either Thrust Lever is advanced. The
Speed Brake Lever will move to the DOWN detent.
¡ All spoiler panels will extend automatically if take-off is rejected and either Reverse Thrust Lever is
positioned for reverse thrust. Wheel speed must be above 60 kt in order for the automatic extension
to take place.
¡ A failure in the automatic functions of the speed brakes is indicated by the illumination of the SPEED
BRAKE DO NOT ARM Light. In the event the automatic system is inoperative, the Speed Brake
Lever must be selected manually to the UP position after landing.
HIGH LIFT DEVICES
¡ High lift leading edge devices are used in combination with the trailing edge flaps to increase lift
during take-off and landing and decrease stall speeds. The trailing edge flaps and leading edge
devices, when extended, increase the wing area and the effective wing camber.
¡ Trailing edge flap position 0-15 provide increased lift; positions 15-40 provide increased lift and drag
to permit slower approach speeds and maneuvering capability. Flap position 15, 30 and 40 are
certified landing flap positions.
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Trailing Edge Flaps
¡ The Flap Lever positions a flap control valve that directs hydraulic pressure to actuate the flap drive
unit to position the flaps. The drive unit also controls the leading edge control valve, so that the
leading edge devices operate in conjunction with the trailing edge flaps.
¡ If an asymmetrical condition develops between the right and left wing trailing edge flaps, hydraulic
power is automatically removed from the flap drive unit.
¡ In the event of hydraulic system B failure, the trailing edge flaps can be alternate operated
(electrically). In this case, control of the flaps is from the flight control panel. The guarded Alternate
Flaps Master Switch actuates a flap bypass valve to prevent hydraulic lock of the flap drive unit and
arms the Alternate Flaps Position Switch. This switch controls an electric motor that operates the
drive unit to extend or retract the trailing edge flaps. No asymmetry protection is provided through
the alternate flap drive system. Alternate Trailing Edge Flap extension 0 to 15 takes about 2 minutes.
Flap Load Relief B737 Classics
¡ A flap load limiter is installed in the trailing edge flap drive system, which is operative at the flaps 40
position. The Flap Lever does not move.
¡ When the flaps are set at 40, the TE-flaps
- retract to 30 if airspeed exceeds 158 knots (737-300 & 500) or 162 knots (737-400).
- extend to 40 when airspeed is reduced below 153 knots (737-300 & 500) or 157 knots (737-400).
Flap Load Relief B737 NG
¡ The Flaps/Slat Electronics Unit (FSEU) provides a TE flap load relief function which is operative at
the flap 30 and flaps 40 positions. The Flap Lever does not move.
¡ When the flaps are set at 40, the TE flaps:
- retract to 30 if airspeed exceeds 163 knots.
- extend to 40 when airspeed is reduced below 158 knots.
¡ When the flaps are set at 30, TE flaps:
- retract to 25 if the airspeed exceeds 176 knots.
- extend to 30 when airspeed is reduced below 171 knots.
Leading Edge Devices
¡ The leading edge devices consist of four flaps and six (737-300/-400) or eight (737-800) slats :
- two flaps inboard of each engine,
- three (ex. 737-300/-400) or four( ex. 737-800) slats outboard of each engine.
¡ Flaps are hinged surfaces that extend by rotating downward from the lower surface of the wing
leading edge. Slats are sections of the wing leading edge that extend forward to form a sealed or
slotted leading edge depending on the trailing edge flap setting.
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Page 9
¡ Leading edge devices are normally extended and retracted by hydraulic power from system B. The
leading edge control valve is controlled by the trailing edge drive unit so that the leading edge
devices operate in conjunction with the trailing edge flaps. When the trailing edge flaps leave the UP
position, the leading edge flaps extend fully, and the leading edge slats extend to an intermediate
position. As the trailing edge flaps extend past the 5 position, the leading edge slats move to FULL
EXTEND. When the flaps are retracted the sequence is reversed.
¡ In the event of hydraulic system B failure the leading edge flaps and slats can be driven to FULL
EXTEND position using power from the standby hydraulic system. In this case the Alternate Flaps
Master Switch energizes the standby pump, and the Alternate Flaps Position Switch, held in the
down position momentarily, extends the leading edge devices.
NOTE. The leading edge devices cannot be retracted by the standby hydraulic system.
¡ Indicator lights on the center instrument panel provide overall leading edge devices position status.
The Leading Edge Device Annunciator on the aft overhead panel indicates the positions of the
individual flaps and slats.
Auto Slat Operation
¡ A dual channel autoslat system provides improved handling qualities at high angles of attack during
take-off or approach to landing.
¡ Works only with flaps 1, 2 or 5 (With Flaps 10° do not forget that slats are fully extended !)
¡ When TE flaps 1 through 5 are selected, the leading edge slats are in the EXTEND position. As the
aircraft approaches the stall angle, the slats automatically drive to the FULL EXTEND position, prior
to stick shaker activation. The slats return to the EXTEND position when the pitch angle is
sufficiently reduced below the stall critical attitude.
Power Transfer Unit
¡ Slat operation is normally powered by system B hydraulics. An alternate source of power is provided
by system A through a Power Transfer Unit (PTU) if a loss of pressure from the system B engine
driven pump is sensed. The PTU provides system A pressure to power a hydraulic motorized pump,
pressurizing system B fluid to provide power for slat and autoslat operation.
¡ A single channel failure causes the AUTO SLAT FAIL Light to illuminate upon Master Caution recall
and extinguish after reset.
¡ A dual channel failure would result in failure of the autoslat system indicated by illumination of the
AUTO SLAT FAIL Light.
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3. CONTROLS & INDICATORS
¡ FLIGHT CONTROL SWITCH
STBY RUD :
- Activates the standby pump & opens the standby rudder shutoff valve to pressurize the standby
rudder power control unit (indicated by the flight control LOW PRESSURE light extinguished).
- Closes Flight Control Shutoff valve, isolating ailerons, elevators & rudder from corresponding
hydraulic system pressure.
- B737 NG : Yaw Damper switch can be turned back on, activating standby Yaw Damper, if both FLT
CONTROL switches are OFF.
OFF
- Corresponding hydraulic system pressure is isolated from ailerons, elevators & rudder.
ON (Guarded position)
- Normal operating position.
¡ ALTERNATE FLAPS MASTER SWITCH
OFF (Guarded position)
- Normal operating position.
ARM :
- 4 subsequent actions :
1) Closes TE Flap Bypass Valve
2) Activates standby pump
3) Arms Standby hydraulic LOW PRESSURE light
4) Arms the Alternate Flaps Position Switch
¡ ALTERNATE FLAPS POSITION SWITCH
(Springloaded from DOWN to OFF)
Functions only when the Alternate Flaps Master Switch is in ARM
DOWN :
- Momentarily selecting DOWN fully extends LE devices using standby hydraulic pressure
- Holding the Switch DOWN electrically extends TE Flaps. (Caution : No asymmetry protection !)
- (Plan a flaps15 landing & remember that it takes approx. 2 min. from 0° to 15°)
UP :
- Electrically retracts TE Flaps
- LE devices remain extended & cannot be retracted by the alternate flap system.
¡ FLIGHT SPOILER SWITCH
(Used for maintenance purposes only)
OFF :
- Closes the respective flight spoilers shutoff valve.
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¡ YAW DAMPER SWITCH
OFF :
- Disengages yaw damper
- Switch drops to OFF automatically when the system B FLT CONTROL switch is positioned to OFF
or STBY RUD or when power interruption to n°1 Transfer Bus for 2 sec..
ON :
- Engages yaw damper to rudder power control unit (B737 NG : does not require hydraulic pressure
to be held in the ON position.
¡ YAW DAMPER INDICATOR
- Indicates yaw damper inputs to the rudder
- B737 NG : Operation of standby yaw damper inputs are not indicated.
¡ STABILIZER TRIM WHEEL
- Provides for manual operation of stabilizer
- Overrides any other stabilizer trim inputs
- Handle should be folded inside Stab Trim Wheel for normal operation.
- Rotates when stabilizer is in motion.
¡ STABILIZER TRIM AUTOPILOT CUTOUT SWITCH
CUT OUT
- Removes power from stabilizer autopilot trim.
¡ STABILIZER TRIM MAIN ELECTRIC CUTOUT SWITCH
CUT OUT
- Removes power from stabilizer main electric trim.
¡ STABILIZER TRIM OVERRIDE SWITCH
OVERRIDE
- Bypasses the control column actuated stabilizer trim cutout switches to restore power to the main
electric trim.
¡ SPEED BRAKE LEVER
DOWN (detent)
- All flight & ground spoiler panels in faired position.
ARMED
- Automatic speedbrake system armed
- Upon touchdown, the speedbrake handle moves to the UP position, and all flight & ground spoilers
extend.
FLIGHT DETENT
- All flight spoilers are extended to their maximum position for inflight use.
UP
- All flight spoilers & ground spoilers are extended to their maximum position for ground use.
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¡ FLAP LEVER
- Selects position of the flap control valve directing hydraulic pressure for the flap driver unit.
- Position of the LE devices is determined bi TE flap position.
- B737 Classics : At position 40, arms the flap load relief system, which automatically causes flap
retraction to Flaps 30 in the event of excess airspeed.
- B737 NG : At position 30 or 40, arms the flap load relief system, which automatically causes flap
retraction to Flaps 25 or 30 in the event of excess airspeed.
¡ FLAP GATES
Prevents inadvertent flap lever movement beyond :
- Position 1 : to check flap position for 1 engine inoperative G/A
- Position 15 : to check flap position for normal go-around.
¡ FLAPS POSITION INDICATOR
- Indicates position of LEFT & RIGHT TE flaps
- Provides TE flaps asymmetry protection circuit.
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BOEING 737 SYSTEMS REVIEW
4. FAULTS & INDICATIONS
VALID FOR
LIGHT
AUTOSLAT
FAIL
FEEL
DIFF PRESS
INDICATION
300
400
500
600
700
800
900
AUTOSLAT FAIL LIGHT (amber)
ILLUMINATED :
- Indicates failure of both autoslat computers
- Indicates failure of single autoslat computer when light
illuminates upon Master Caution recall and extinguishes .
when reset.
X
X
X
X
X
X
FEEL DIFF LIGHT (amber)
Armed when the trailing edge flaps are UP
ILLUMINATED :
- Indicates excessive differential pressure in the elevator feel
computer.
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
LE FLAPS
EXT
LE FLAPS EXTENDED LIGHT (green)
ILLUMINATED :
- All LE flaps extended & all LE slats in intermediate.
Position (TE flap positions 1 & 5)
- All LE devices fully extended (TE flap positions 15 through
40)
LE FLAPS
TRANSIT
LE FLAPS TRANSIT LIGHT (amber)
ILLUMINATED :
- Any leading edge device in transit, or not in programmed
position with respect to TE Flaps.
Note : Light is inhibited during autoslat operation in flight
MACHTRIM
FAIL
MACH TRIM LIGHT (green)
ILLUMINATED :
- Indicates failure of both FCC Mach Trim channels
- Indicates failure of a single Mach Trim channel when light
illuminates upon Master Caution Recall & extinguished
when reset.
Note : If both channels INOP
B737 Classics : do not exceed M.74
B737 NG : do not exceed 280 kt / M.82
SPEED BRAKE
ARMED
SPEED BRAKE
ARMED
SPEED BRAKE
DO NOT ARM
SPEED BRAKE ARMED LIGHT (green B737 Classics or
amber on B737 NG)
(Light is deactivated when Speed Brake lever is in DOWN
position)
ILLUMINATED :
- Indicates valid auto Speedbrake system inputs
SPEED BRAKE ARMED LIGHT (amber)
(Light is deactivated when Speed Brake lever is in
DOWN position)
ILLUMINATED :
- Indicates abnormal condition or test inputs to automatic
speedbrake system
- Always illuminated after landing at approx. 60 kt
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BOEING 737 SYSTEMS REVIEW
VALID FOR
LIGHT
SPEED BRAKE
EXTENDED
SPEEDTRIM
FAIL
YAW
DAMPER
INDICATION
400
500
SPEED BRAKE EXTENDED LIGHT (amber)
ILLUMINATED - In flight
Speedbrake lever is > the ARMED position and either :
- TE Flaps extended more than flaps 10 or
- Radio Altitude < than 800 ft
ILLUMINATED - On ground
- Speedbrake lever is in the DOWN detent position
- Ground spoilers are not stowed.
SPEED TRIM FAIL LIGHT (amber)
ILLUMINATED :
- Indicates failure of both FCC Speed Trim Channels
- Indicates failure of single FCC Speed Trim channel when
light illuminates upon Master Caution recall and
extinguishes when reset.
Note : System is armed from 100-300 kt (B737 Classics)
& from 100 kt to M.050 (B737 NG) + 10 sec. after
liftoff, 5 sec. following release of trim switches,
N1 > 60%, autopilot not engaged.
YAW DAMPER LIGHT (amber)
ILLUMINATED :
- Yaw damper is not engaged.
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Ludovic ANDRE / version 00
300
600
700
800
900
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
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BOEING 737 SYSTEMS REVIEW
FLIGHT CONTROL SURFACE LOCATION
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Page 15
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BOEING 737 SYSTEMS REVIEW
ROLL CONTROL SCHEMATIC
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BOEING 737 SYSTEMS REVIEW
ELEVATOR CONTROL SCHEMATIC
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BOEING 737 SYSTEMS REVIEW
STABILIZER CONTROL SCHEMATIC
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Page 18
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BOEING 737 SYSTEMS REVIEW
YAW CONTROL SCHEMATIC (B737 CLASSICS)
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Page 19
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BOEING 737 SYSTEMS REVIEW
SPEED BRAKES SCHEMATIC (B737 CLASSICS)
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Page 20
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BOEING 737 SYSTEMS REVIEW
SPEED BRAKES SCHEMATIC (B737 NG)
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Page 21
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BOEING 737 SYSTEMS REVIEW
TRAILING EDGE SCHEMATIC
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BOEING 737 SYSTEMS REVIEW
LEADING EDGE DEVICES SCHEMATIC (B737 CLASSICS)
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Page 23
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BOEING 737 SYSTEMS REVIEW
LEADING EDGE DEVICES SCHEMATIC (B737 NG)
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Page 24