Flight Controls Flashcards
The flight controls are fly-by-wire,
which is an electronic, rather than a mechanical system for operating the flight controls.
Control wheel & rudder pedals provide conventional control feel and pitch responses to speed and trim changes.
The electronic components
reduce pilot workload and at the same time provide enhanced handling qualities.
Jam override mechanisms allow pilots to maintain airplane control by applying
force to the other column or wheel to overcome the jam.
The primary flight control system is highly redundant, with three operating modes:
normal mode,
secondary mode,
and direct mode.
Roll control uses
two ailerons, 14 spoilers and two flaperons.
The flaperons operate in both
low and high speed flight.
The ailerons assist in roll control during low speed flight only. They are locked out
during high speed flight.
The flaperons provide additional lift by drooping when the flaps extend.
There is no flight deck indication of flaperon droop.
The ailerons also
move down for
flaps 5, 15 and 20
to improve take-off performance.
Two different hydraulic systems power the PCUs for
each aileron and flaperon.
Two different ACEs control each aileron and flaperon.
The hydraulic and control arrangement provides redundancy.
Should a single system be lost,
the ailerons and flaperons are still operational.
Spoilers work asymmetrically when augmenting roll control.
Spoilers 5 and 10 are
only available during low speed operation.
Roll trim is provided by two aileron trim switches. Moving both switches together in the desired direction sends signals to reposition
the ailerons, flaperons and spoilers.
When aileron trim is applied the control wheels are displaced proportionally in the direction of trim switch movement.
Aileron trim is inhibited with the autopilot engaged.
Yaw control is provided by
the rudder pedals,
rudder trim system,
yaw dampers
and the rudder ratio system.
Rudder deflections are proportional to rudder pedal movements.
Hydraulic pressure from all 3 hydraulic systems is used to operate and trim the rudder.
Each PCU is powered by 1 of 3 hydraulic systems and controlled by
right, center and left 1 Actuator Control Electronics (ACEs).
Two rudder trim speeds are available.
Low rate rudder trim is commanded by
High rate rudder trim is commanded by rotating the control
rotating the control to the detent.
past the detent.
The control is spring loaded to the neutral position.
The manual trim input can be cancelled by pushing the MANUAL TRIM CANCEL switch.
The switch has no effect
Thrust Asymmetry Compensation (TAC) inputs.
There are no separate yaw dampers on the aircraft. Command signals from the PFCs to the ACEs and PCUs provide
turn coordination and dutch roll damping.
In the secondary mode, yaw damping is normally degraded,
but may be inoperative for certain multiple failures.
In the direct mode, yaw damping
is not available.
There is no separate rudder ratio unit on the aircraft.
Based on airspeed, the PFCs calculate the amount of rudder deflection
required.
Full rudder deflection is available at
low airspeeds.
As airspeed increases, the PFCs gradually reduce rudder deflection.
This ensures
structural integrity of the rudder.
In the secondary and direct modes, rudder response defaults to fixed ratios
and is determined by flap position.
With flaps up, rudder response is less
than with flaps down.
When a single gust hits the vertical tail,
gust suppression transducers send signals to the ACEs
which in turn send this data to the PFCs
to adjust PCU commands to dampen
the gust side force.
Pitch control is similar to conventional airplanes.
However, the control column does not directly position the elevator in flight.
The control commands the PFCs to
generate a pitch maneuver.
Elevator feel forces vary based on airspeed. Generally, control forces increase
as airspeed increases.
The center and right hydraulic systems power the stabilizer PCUs and they are controlled by all 4 ACEs.
On the ground, primary pitch trim is controlled by dual trim switches
There is a stabilizer trim indicator on each side of the control stand.
The scale is in units of stabilizer trim and the white diamond indicates
on each control wheel.
current stabilizer position.
Stabilizer trim green band indicates the allowable stabilizer range
for take-off as calculated by the FMC,
using take-off weight, CG and take-off thrust data.
not displayed in flight.
The green band is
A nose gear oleo pressure switch provides an automatic cross check of CG
to ensure the correct green band is displayed.
If the FMC computed stabilizer green band conflicts with the nose gear pressure switch,
an EICAS advisory message
STAB GREENBAND displays.
In flight, pitch trim signals from the pitch trim switches and the autopilot do not
position the stabilizer directly.
automatic trimming is with the autopilot. Adjusting the speed sends pitch trim signals to change the trim reference speed in the PFCs.
The PFCs then send signals through the ACEs to reposition the elevators.
The stabilizer moves to a new trim position required by the new reference speed and the elevators streamline with the stabilizer.
When the autopilot is not engaged, as the airspeed changes,
the pitch control system provides conventional characteristics by requiring the pilot to make control column inputs of trim changes to maintain a constant flight path.
Manual trim is necessary only
when changing airspeed.
Manual trim switches are inhibited with the
autopilot engaged.
Pitch trim switches may be overridden by moving the control column in
the opposing direction.
Another way to manually set trim is to use the alternate pitch trim levers on the control stand.
The levers must always be moved together.
They are spring loaded to the
center neutral position.
The Alternate Pitch trim levers are mechanically linked via cables to the
stabilizer trim control modules or STCMs.
The Alternate Pitch Trim levers move the trim reference speed (NORMAL MODE) and also move the stabilizer (ALL MODES)
by setting valves in the STCMs which control hydraulic fluid to move the stabilizer.
With one STCM inoperative,
the stabilizer moves at a reduced rate.
Moving the alternate pitch trim levers with the autopilot engaged moves the stabilizer but will not disengage the autopilot.
Note: the alternate pitch trim levers should not be used
with the autopilot engaged, or during stall or overspeed protection.
Alternate pitch trim commands have priority over wheel pitch trim commands in all flight control modes.
Spoiler panels are numbered 1 to 14
from left to right.
When used as speed brakes, spoilers are paired
and work symmetrically.
Each symmetrical pair of spoilers is controlled by the same ACE, and operated by
the same hydraulic system.
All three hydraulic systems supply the spoilers.
Each hydraulic system is dedicated to a different set of spoiler pairs to provide isolation and maintain symmetrical operation.
Failure of the ACE or hydraulic system
renders the associated pair inoperative.
f the speedbrake lever is moved close to the UP position, spoiler panels
4 and 11 operate symmetrically as speedbrakes.
Moving the speedbrake lever to the UP position signals spoiler panels to extend to the full up position.
Spoilers 5 and 10 are not available in flight as speedbrakes.
The high lift control system consists of flaps and slats.
They have 3 modes of operation; primary, which is hydraulic,
secondary and alternate which
are both electric.
Primary mode operation of the flaps and slats uses the
center hydraulic system.
To prevent inadvertent flap retraction during take-off or go-around there are gates at the
1 and 20 flap positions.
The flap and slat position indicator is displayed on EICAS.
Normally, the indicator is not displayed until
slats begin to extend.
When the flaps and slats are selected UP, the indicator is removed from the EICAS
10 seconds after the flaps and slats reach the up position.
In the normal mode during manual flight,
pilot control inputs through control column,
wheel, rudder pedals and speedbrake lever
are converted to analog signals.
These signals go to
4 Actuator Control Electronics, or ACEs
Digital signals from the ACEs are sent to
3 Primary Flight Computers, or PFCs.
The PFCs calculate the pilot flight control position commands and then sends
them back to the ACEs.
The PFCs also receive
airspeed data,
inertial reference data,
Angle of Attack
and flap position data
from other airplane systems.
The ACEs convert the signals back to analog form and send them
to the Power Control Units, or PCUs.
When the autopilot is engaged,
the autopilot sends commands to the PFCs
which in turn are sent to the ACEs in the same manner as
pilot control inputs.
The autopilot is only available during
normal mode operation.
After the hydraulic systems are shut down, the PFCs self test.
EICAS will display various
alert and status messages during the test sequence.
The flight controls synoptic displays various failure indications and the trim indicators blink.
When the test is complete the EICAS messages disappear; the synoptic and trim indicator return to normal.
Overspeed protection limits the trim reference speed so that trim is inhibited in the nose down direction at
VMO / MMO.
The pilot must apply continuous forward column force to exceed VMO / MMO.
Use of the alternate pitch trim levers does not reduce column forces.
The forward column force needed to keep the airplane in overspeed
reduces with bank angle.
If this 35 ° boundary is exceeded, the control wheel force rolls the airplane back to
within 30 ° of bank. This roll command can be overridden by the pilot through the control wheel.
Bank angle protection functions in both manual and autopilot operation. However, the autopilot disengage bar
disables bank angle protection.
Bank angle protection is not available in the
SECONDARY and DIRECT modes, otherwise roll control is very similar to the normal mode.
Spoiler panels 5 and 10 are always locked out.
There is no aural stall warning. A stick shaker activates at
the minimum speed displayed on the PFD airspeed indication.
Stall protection features reduce the possibility of stick shaker activation.
The lowest speed to which the airplane can be trimmed is
the minimum maneuvering speed.
Nose-up trim is inhibited below this speed.
When flying near the stall speed, column forces increase and the pilot must apply continuous aft column force to
maintain airspeed below minimum maneuvering.
Use of the alternate pitch trim levers will not relieve the column force.
If the speed continues to reduce to halfway into the PFD airspeed amber band, EICAS will display
the caution message, AIRSPEED LOW.
If speed decreases to near stick shaker, the autothrottle automatically activates in the appropriate mode (SPD or THR REF) and increases thrust to maintain
minimum maneuvering speed.
The autothrottles will not automatically engage
when the pitch mode is
FLCH or TOGA, or
when below 400 ft above field elevation on take-off
or 100 ft RA on approach.
Note: during descent in VNAV SPD,
if the autothrottles are in hold mode,
autothrottle stall protection is not supported.
TAC continually monitors engine thrust levels and will automatically add rudder to compensate yaw for thrust level differences of
10 % or more.
The TAC is available only in the Normal Flight Control Mode.
When TAC is operating, the pilot can still recognize the initial onset of an engine failure through
airplane roll / yaw cues.
These roll / yaw cues are greatly reduced when compared to an airplane operating without TAC.
Yaw compensation is indicated to the pilots by a shift in the rudder pedals and
change in the rudder trim indication.
TAC is automatically armed above 70 kt and is operational in manual and auto flight. It is not available during
reverse thrust
or when automatically disengaged due to a system malfunction
or loss of engine thrust data.
A switch on the overhead panel allows the TAC system
to be turned off.
The EICAS advisory message THRUST ASYM COMP
displays if TAC is
automatically or manually disconnected.
Below 210 kt, a wheel to rudder crosstie function is available.
This allows control wheel inputs to deflect the rudder up to
8 ° to help to control the initial effects of an engine failure.
This feature is available in the normal mode only.
Flap and slat extension is inhibited above 20,000 ft and 265 kt airspeed.
This prevents deployment if the flap lever
is inadvertently moved.
Moving the flap lever out of the up position to 1 sends a signal to
two Flap and Slat Electronic Units (FSEUs),
which control and monitor flap and slat operation in
both primary and secondary modes.
The slat hydraulic motor operates 1 inboard and 6 outboard slats plus 1 Krueger flap on each wing.
seal between the engine and the inboard slat.
They extend with the slats at flaps 1 and are either up or down.
There is no intermediate position.
Moving the FLAP handle from UP to 1 extends the slats to
Moving the handle between 5 and 20 only extends the
mid range.
trailing edge flaps.
When flap 5 is selected,
the inboard and outboard trailing edge flaps
move to the 5 position.
Flaps 5, 15 and 20 are
take-off flap settings.
Selecting flaps 25 or 30
initially moves the slats to the fully extended position,
then
the trailing edge flaps
move to the flaps 25 or flaps 30 position
as selected.
In primary mode, flap LOAD RELIEF operates for flaps 15 through 30.
LOAD RELIEF displays on the EICAS flap position display if flap placard speed for one of these positions is exceeded.
The flaps retract to a position
adequate for the speed.
If LOAD RELIEF activates, retraction is limited to flap 5.
When airspeed is sufficiently reduced,
the flaps return to the selected position.
LOAD RELIEF also displays if the flap lever is moved out of UP
while flaps are inhibited.
Stall protection is augmented by the autoslat system.
If the slats are in the midrange position
when stall speed is approached they extend
automatically to the fully extended position to increase lift.
The autoslat system works in the primary mode only.
Automatic deployment after landing
requires the SPEEDBRAKE lever to be in the ARMED position.
When the speedbrake is in the ARMED position the EICAS message
SPEEDBRAKE ARMED displays.
After touchdown the speedbrake lever moves to the UP position,
and the spoiler panels extend automatically
providing the landing gear is fully on the ground, and not tilted,
and thrust levers are at idle.
Auto speedbrakes are not available
in the secondary and direct modes.
With the SPEEDBRAKE lever not in the ARMED position, the spoilers will extend automatically when
either reverse thrust lever is raised to its interlock stop.
If the SPEEDBRAKE lever is not in the down detent for take-off
and take-off thrust is selected on either engine,
the SPEEDBRAKE lever is
driven to the down position.
If there is a failure to manually extend the speedbrakes
during a rejected take-off,
pulling either reverse lever to the reverse idle detent automatically
moves the SPEEDBRAKE lever to the UP position, extending the spoilers.
When the Primary Flight Computers can no longer support the normal mode,
due to internal faults or lack of required information from other aircraft systems,
they automatically revert to
the secondary mode.
In SECONDARY mode some flight control functions are degraded and some
are lost completely.
In secondary mode what is not available?
What may be lost or degraded?
Autopilots, auto speedbrakes and envelope protection features are not available
Yaw damping may be lost or degraded
The Primary Flight Control system, automatically switches to direct mode if
additional failures occur
or if the Primary Flight Control computers disconnect switch is moved to the DISC position by the pilot.
When the flight control mode automatically reverts to DIRECT mode,
the EICAS caution message PRI FLIGHT COMPUTERS displays.
The flight controls are now operated directly by pilot inputs to
the ACEs. The PFCs are no longer used.
Roll control in the secondary and direct modes is very similar to roll control in the normal mode.
Bank angle protection is
Spoilers 4 and 11 are mechanically controlled for roll and spoilers 5 and 10 are always locked out.
not available in either the secondary or direct mode.
Yaw control in the secondary and direct modes results in the loss or degradation of a number of features.
Wheel to rudder cross tie
TAC
Yaw Damping (normally degraded in secondary mode but may be inoperative for certain multiple failures)
Gust suppression
In addition manual trim cancel is not available in the direct mode.
In the secondary and direct modes,
elevator feel changes to two fixed levels of force.
Control column forces are
lower with flaps extended and higher with flaps up.
In the secondary and direct flight control modes
the control columns command a
proportional elevator deflection instead of
a maneuver command.
In the unlikely event of a complete electrical system shut down
A backup cable system from the flight deck to the stabilizer and selected spoilers allows
the pilot to fly straight and level
Automatic pitch compensation for the following is not available in the
secondary and direct modes:
thrust changes, gear configuration changes, turbulence,
flap and speedbrake configuration changes
and turns to 30 degree bank angle.
When the primary mode fails to move the slats or flaps, automatic engagement of
the caution message,
SLATS PRIMARY FAIL
or FLAPS PRIMARY FAIL as appropriate.
Once engaged the secondary mode remains engaged until the affected slats and /
or flaps are fully retracted or hydraulic power is restored.
The normal flap position indicator shown on the EICAS is expanded in the
secondary mode.
The slat and flap positions are shown for each wing.
As the slats and flaps are electrically powered in the secondary mode,
movement is
significantly slower.
When the secondary mode engages with the slats in the UP position,
providing airspeed is less than 239 kt,
selecting flaps 1 extends the slats to
fully extended.
If the slats are in the mid-range position when the secondary mode engages,
they remain in that position until the flaps are either retracted UP
or extended beyond
20
If the airspeed becomes excessive with the slats down
in secondary mode,
the slats retract to
the mid position and LOAD RELIEF displays.
The EICAS caution message FLAP/SLAT CONTROL displays if both
The slats and flaps must now be positioned using
the primary and secondary modes fail.
the ALTERNATE mode.
The alternate mode must be selected manually.
In the alternate mode,
extend and retract signals bypass the FSEUs
and are sent directly to
The ALTN FLAPS selector is used to extend or retract slats and flaps.
Slat extension is limited to
And Flaps limited to
the slat / flap electric motors
mid-range and flaps are limited to 20.
Flap / slat movement must be closely monitored in direct mode as there is no
asymmetry protection.
The switch is selected to OFF when the correct position is reached.
Extension time from 5 to 20 is similar to secondary mode.
During flap / slat retraction, normal sequencing does not occur.
Slat retraction is inhibited until the flaps are UP.
EICAS advisory message STABILIZER C or STABILIZER R displays if
the respective stabilizer trim control module is inoperative.
The message appears if the respective switch is in CUTOUT
or uncommanded stabilizer movement has caused an auto shutdown.
The stabilizer remains operative,
at a reduced rate, through the remaining stabilizer trim control module.
Pitch trim switches or alternate pitch trim levers maybe used.
With both switches in CUTOUT,
the EICAS displays STABILIZER CUTOUT advisory message.
In the normal mode, pitch trim is
still available.
Pitch trim inputs, through the PFCs,
position the elevator to trim the airplane.
EICAS will display warning message STABILIZER if
both stabilizer trim control modules automatically shutdown or fail.
The message will also appear if an auto shutdown does not stop unwanted motion.
Place both:
With both STAB CUTOUT switches in CUTOUT,
the EICAS warning message changes to:
STAB CUTOUT switches to CUTOUT. STABILIZER CUTOUT advisory message.
STABILIZER CUTOUT advisory message.
If the auto speedbrakes feature becomes inoperative,
the EICAS advisory message AUTO SPEEDBRAKE displays.
Do not
arm the speedbrake as inadvertent extension may occur.
After landing, manually extend the speedbrakes.
Descending below 800 ft Radio Altitude, or selecting landing flaps,
with speedbrakes extended, causes
the EICAS caution message SPEEDBRAKE EXTENDED to appear.
The message will also display with speedbrakes extended and thrust levers not
in idle.
When a flap asymmetry is detected the flap drive motors shut down
and the EICAS will display the caution message,
FLAPS DRIVE.
The flaps cannot
be repositioned from this failed position.
The flaps position indication on EICAS turns amber.
The same message, FLAPS DRIVE,
displays if both hydraulic and electric flap drive motors fail,
or if uncommanded flap motion is detected.
When a slat asymmetry is detected the slat drive motors shutdown
and the EICAS displays the caution message, SLATS DRIVE.
The slats cannot
be repositioned from this failed position.
The position indication on the EICAS turns amber.
The same message, SLATS DRIVE,
displays if both hydraulic and electric slats drive motors fail,
or if uncommanded slat motion is detected.
With a Hyd press C inop
Slats will extend beyond midrange when airspeed is below 239 kt.
For go-around, do not exceed
239 kt until slats retract to midrange.
When the caution message HYD PRESS SYS L or R is displayed,
roll rate may be reduced in flight.
Speedbrake effectiveness may
be reduced in flight and during landing.
When a caution message announces two hydraulic system failures,
there are several items that are common to all of these situations:
Handling degraded, pitch & roll capability reduced(fewer operating control surfaces)
Plan to land @ nearest suitable
Ground Prox Override
Flaps 20 Vref 30+20 for landing (improves maneuvering)
Crosswind limit for landing 20 kts
Roll rate may be reduced in flight, speedbrakes may be reduced in flight and during landing
With a caution HYD PRESS L & C
Plan additional time for slower flap & slat operation
Do not arm speedbrake - manually extend after landing
Crosswind limit 20 kts
With caution message HYD PRESS R + C note:
Do not exceed .87 M
If HYD PRESS SYS R + C remains:Both Stabilizer Cutout switches to cutout (prevents display of STABILIZER message)
Do not exceed current airspeed ( nose down elevator authority is limited)
Plan additional time for slower flap & slat operation
Slats will extend beyond midrange when airspeed below 239 kts
For go around do not exceed 239 kt until slats retract to midrange
Do not arm speed brake - manually extend after landing
The Flight Control DC electrical system is a dedicated power source for
the Primary Flight Control system.
Primary power for the Flight Control DC electrical system comes from
Permanent Magnet Generators (PMGs) housed within
each backup generator.
Variable frequency PMG AC power is used by individual Power Supply
Assemblies (PSAs) to provide DC power to
the three Flight Control DC busses.
To ensure a high level of system reliability,
each PSA also has multiple DC power sources.
