What are the three operating modes of the primary flight controls?
Normal, secondary, direct
How are the secondary flight controls (flaps and slats) powered?
Hydraulically powered with an electrically powered backup system
EICAS caution message FLIGHT CONTROLS
If either of the following occurs:
Multiple actuator control electronics (ACEs) and/or hydraulic system failures cause the loss of a significant number of control surfaces
Other significant flight control system faults are detected
If there is a loss of all hydraulic power how are flight controls allowing pitch and roll?
The electrically actuated stabilizer and two spoiler pairs allow pitch and roll control using the primary pitch trim switches, alternate pitch trim switches, and roll using the control wheel
Pitch control is provided by:
Two elevators
A movable horizontal stabilizer
Role control is provided by:
Two flapperons
Two ailerons
Fourteen spoilers
When are ailerons locked out?
During high speed flight where the flaperons and spoilers provide sufficient roll control.
The ailerons operate to augment roll control during slow speed flight
Flight control system normal mode:
Four ACEs receive pilot control inputs and send these signals to three PFCs
When autopilot is engaged, system commands are sent directly to the PFCs
Auto pilot is only available during normal mode
How many flight control self tests are there?
Three,
one after landing (hydraulics on, flaps and speed brakes retracted, speed less than 20 knots for 5 seconds)
Second cycle starts after hydraulics are depressurized and takes about 55 seconds
The third is after these other tests are complete, engines shut down, PMG power is off. Takes about 90 seconds
If any tests are skipped or interrupted a fault condition may result with a status message requiring maintenance
Flight envelope protection in normal mode provides?
Stall protection, over speed protection, bank angle protection
When do PFCs automatically revert to secondary mode?
When inertial or air data is insufficient to support normal mode
Or when all slat and flap position data is unavailable
Summary of flight controls secondary mode
ACEs receive and process pilot inputs and send these signals to the three PFCs
PFCs send simplified computations to generate flight control surface commands back to the ACEs where they are sent to the flight control surface actuators
All flight control surfaces remain operable
Yaw damping is degraded
What seven functions are not available in the secondary flight control mode or the direct mode?
Autopilot
Auto speed brakes
Pitch compensation
Gust suppression
Roll/yaw asymmetry compensation
Tail strike protection
Envelope protection
EICAS caution message FLIGHT CONTROL MODE
Displayed when the primary flight control system is in the secondary mode.
This mode cannot be manually selected
When do the ACEs automatically transition to the DIRECT mode?
When they detect failure of all three PFCs or lose communication with the PFCs
Direct mode can be manually selected by moving the PRIMARY FLIGHT COMPUTERS disconnect switch to DISC
In direct mode, how are controls actuated?
The PFCs no longer generate control surface commands. Pilot inputs received by the ACEs are sent directly to the control surface actuators
All flight controls remain operable in direct mode, yaw damping is degraded
Which EICAS caution message is displayed when in direct mode?
PRI FLIGHT COMPUTERS
How does pitch trim differ on ground vs inflight?
On the ground, trim switches directly position the stabilizer
In flight, they do not position stabilizer directly. They make inputs to the PFCs to change the trim reference speed (the speed at which the airplane would eventually stabilize if there were no control column inputs)
NOTE: in secondary or direct mode, the primary and alternate trim systems directly position the stabilizer and operate the same on the ground or inflight
Alternate trim system
Dual switches located on the control stand
Linked electrically to the horizontal stabilizer trim actuator, and then mechanically to the stabilizer
Secondary and direct modes do not provide automatic pitch compensation for:
Flaps and Speedbrake configuration changes
Gear configuration changes
Thrust changes
Turns at 30 degree bank angle
Turbulence
EICAS advisory message STABILIZER L2 or STABILIZER R2
One of the two channels is inoperative due to automatic shutdown or failure
Stabilizer remains operative through remaining channel
If the affected channel cannot be isolated then both channels are shut down
EICAS warning message STABILIZER
Both stabilizer channels automatically shut down or fail
Message also displays if the automatic shutdown fails to stop uncommanded motion
EICAS advisory message STABILIZER CUTOUT
Both trim cutout switches have been placed in cutout position
With both switches in cutout position the STABILIZER warning message is not displayed
NOTE: does not apply if automatically shut down
What happens if control column cutout function remains active for 20 seconds?
STABILIZER L2 or R2 EICAS advisory is displayed
Flight controls system reverts to direct mode
Uncommanded input is removed by system shutdown
