LANE AVAILABILITY PFCS MODE MESSAGE MESSAGE TYPE
2-2-1/0 NORMAL FLIGHT CONTROL SYS STATUS
2-1/0-1/0 NORMAL FLIGHT CONTROL SYS STATUS
1/0-1/0-1/0 DIRECT PRI FLIGHT COMPUTERS AUTO SPEEDBRAKE THRUST ASYM COMP FLIGHT CONTROL SYS AUTO SPEEDBRAKE THRUST ASYM COMP CAUTION ADVISORY ADVISORY STATUS STATUS STATUS
The system operates normally with one PFC lane failed, in the 3-3-2 configuration. There is no flight deck indication in this configuration.
The EICAS caution message FLIGHT CONTROL MODE indicates that the PFCS is in secondary mode.
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PFCS -PFC -FUNCTIONAL DESCRIPTION
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PFCS -PFC CONTROL LAWS -FUNCTIONAL DESCRIPTION
General
The PFCs software includes the flight control laws. They calculate the control surface commands to set the desired airplane stability and control. The calculation uses data inputs from the pilots, the autopilot, and other data from the air and inertial sensing systems.
The PFCs calculate control commands for:
*
The ailerons, flaperons and spoilers for roll control
*
The ailerons and some spoilers for lockout during cruise
*
The ailerons and flaperons for droop control during flap extension
*
The spoilers during speedbrake control in flight and on the ground
*
The elevators for pitch control
*
The elevator feel actuator
*
The stabilizer for elevator offload (long term pitch trim), column cutout, and stabilizer auto shutdown
*
The rudder for yaw control, yaw damping, rudder ratio, and wheel-rudder cross-tie
*
The rudder trim actuator.
The control laws also include stability augmentation and protection functions.
Stability Augmentation
There is a stability augmentation function for the pitch and yaw control. Stability augmentation controls the airplane attitude to simulate the natural reaction of the airplane that the pilots expect.
The control laws calculate yaw damping and turn coordination commands. A gust suppression function makes the ride quality better and reduces the pilots’ work load.
In pitch stability augmentation, the PFCs use the control laws to calculate the elevator control commands for speed stability and flare compensation.
Protection Functions
The control laws contain several different limits to supply flight envelope protection in the three axes of control. The PFCs calculate protection functions for:
*
Bank angle
*
Overspeed
*
Stall
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Thrust asymmetry compensation
*
Overyaw.
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PFCS -PFC CONTROL LAWS -FUNCTIONAL DESCRIPTION
The bank angle protection supplies a roll command opposite to the bank. The overspeed protection supplies a pitch up command when the speed is more than the maximum. The stall protection supplies a pitch down command. The thrust asymmetry compensation (TAC) automatically controls the rudder movement to make allowance for asymmetrical thrust from the engines. The overyaw protection operates through the wheel-rudder cross-tie function to decrease the yaw command.
The bank angle and the stall protections supply more resistive force to the controls. The pilots can override the protection functions when they move the controls more than the limit. There is no increased force on the controls for the other protection functions.
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PFCS -PFC CONTROL LAWS -FUNCTIONAL DESCRIPTION
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PFCS -PFC DISCONNECT SWITCH
Purpose
The PFC disconnect switch lets the pilot select the direct mode of operation.
Physical Description
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