Turbulence compensated throttle control system

Claim 2

In combination wIth an automatic speed control system for an aircraft employing means responsive to a position command signal, an apparatus providing said position command signal substantially free from turbulence noise, comprising: means for processing a signal representative, respectively, of air speed error relative to selected air speed and inertial longitudinal acceleration of the aircraft to provide a first control signal; means responsive to said signal representative of inertial longitudinal acceleration of the aircraft for providing a second control signal; and means subtracting said second control signal from said first control signal to provide said position command signal compensated for overtravel due to engine lag.

Claim 3

In combination in an aircraft throttle control system having a throttle position servo: means for processing a signal representative respectively of air speed error relative to selected air speed and inertial longitudinal acceleration of the aircraft to provide a first control signal; means responsive to said signal representative of inertial longitudinal acceleration of the aircraft for providing a second control signal; means for subtracting said second control signal from said first control signal to provide a throttle command signal compensated for overtravel due to engine lag time; and means for coupling said compensated throttle command signal to the input of said throttle position servo.

Claim 4

In combination in an aircraft throttle control system having a throttle position servo: means for processing a signal representative respectively of air speed error relative to selected air speed and inertial longitudinal acceleration of the aircraft to provide a first control signal; means responsive to said signal representative of inertial longitudinal acceleration of the aircraft for providing a second control signal; means for subtracting said second control signal from said first control signal to provide a throttle command signal compensated for overtravel due to engine lag time; and means for coupling said compensated throttle command signal to the input of said throttle position servo.

Claim 5

The invention according to claim 2 wherein said means responsive to said signal representative of inertial longitudinal acceleration comprises amplifier means.

Claim 6

An autothrottle control system comprising in combination: integrator circuit means having an input terminal and an output terminal; means for providing the gain weighted sum of signal representative of air speed error and air speed control damping, said means having an output terminal; said input terminal of said integrator circuit coupled to said output terminal of said means for providing the gain weighted sum; the output of said integrator circuit means coupled to the input terminal of a summing circuit means; said summing circuit means also responsive to a separately processed signal representative of air speed control damping; servo means having an input terminal coupled to the output terminal of said summing circuit means and an output terminal coupled to the throttle of said autothrottle control system, for driving said throttle; synchronizing amplifier means having an input terminal coupled in circuit between the output terminal of said summing circuit means and the input terminal of said servo means, said synchronizing amplifier means further having an output terminal; switching means for coupling said output terminal of said synchronizing amplifier means to the input terminal of said integrator circuit means when the forward or aft throttle limit of said throttle is reached thereby synchronizing the throttle position to zero; means for detecting a change in the sign of signals present

Claim 7

An autothrottle control system comprising in combination: integrator circuit means having an input terminal and an output terminal; means for providing the gain weighted sum of signal representative of air speed error and air speed control damping, said means having an output terminal; said input terminal of said integrator circuit coupled to said output terminal of said means for providing the gain weighted sum; the output of said integrator circuit means coupled to the input terminal of a summing circuit means; said summing circuit means also responsive to a separately processed signal representative of air speed control damping; servo means having an input terminal coupled to the output terminal of said summing circuit means and an output terminal coupled to the throttle of said autothrottle control system, for driving said throttle; synchronizing amplifier means having an input terminal coupled in circuit between the output terminal of said summing circuit means and the input terminal of said servo means, said synchronizing amplifier means further having an output terminal; switching means for coupling said output terminal of said synchronizing amplifier means to the input terminal of said integrator circuit means when the forward or aft throttle limit of said throttle is reached thereby synchronizing the throttle position to zero; means for detecting a change in the sign of signals present

Claim 8

In combination in an autothrottle control system for an aircraft; first means for providing a signal representative of air speed error; second means for providing a signal representative of longitudinal acceleration; first adder circuit means having first and second input terminals and an output terminal; first limiter circuit means; first amplifier circuit means; first filter circuit means; said first limiter circuit means, first amplifier circuit means and first filter circuit means coupled in series circuit between said first means for providing a signal representative of air speed error and said first input terminal of said first adder circuit means; second adder circuit means having first and second input terminals and an output terminal, said first input terminal coupled to said second means for providing a signal representative of longitudinal acceleration; rate limiTed lag circuit means having an input terminal and an output terminal; washout and lag circuit means having third adder circuit means, first integrator circuit means, fourth adder circuit means and second amplifier circuit means connected in series circuit between said second means for providing a signal representative of longitudinal acceleration and said input terminal of said rate limited lag circuit means; said rate limited lag circuit having fifth adder circuit means, second limiter circuit means, third amplifier circuit means, and second integrator circuit means coupled in series circuit between said input and output terminals thereof; said output terminal of said rate limited lag circuit means coupled to said second input terminal of said second adder circuit means; second filter circuit means having an input terminal and an output terminal, said input terminal connected to said output terminal of said second adder circuit means; fourth amplifier circuit means coupled between said output terminal of said second filter circuit means and said second input terminal of said first adder circuit means; sixth adder circuit means having first and second input terminals and an output terminal; third integrator circuit means having an input terminal and an output termial; seventh adder circuit means having first and second input terminals and an output terminal; said input terminal of said third integrator circuit means coupled to said output terminal of said sixth adder circuit means, said output terminal of said integrator circuit means coupled to said first input terminal of said seventh adder circuit means; servo and throttle means coupled in series between the output of said seventh adder circuit means and the propulsion means for the aircraft; synchronizing amplifier means having an input terminal and an output terminal, said input terminal coupled to the output terminal of said seventh adder circuit means; tachometer means having an input terminal coupled to the output of said servo means, and an output terminal coupled to said second input terminal of said sixth adder circuit means; and switching means coupling said first input terminal of said sixth adder circuit means to said output terminal of said first adder circuit means or to said output terminal of said synchronizing amplifier means.

Claim 9

In combination in an autothrottle control system for an aircraft; first means for providing a signal representative of air speed error; second means for providing a signal representative of longitudinal acceleration; first adder circuit means having first and second input terminals and an output terminal; first limiter circuit means; first amplifier circuit means; first filter circuit means; said first limiter circuit means, first amplifier circuit means and first filter circuit means coupled in series circuit between said first means for providing a signal representative of air speed error and said first input terminal of said first adder circuit means; second adder circuit means having first and second input terminals and an output terminal, said first input terminal coupled to said second means for providing a signal representative of longitudinal acceleration; rate limiTed lag circuit means having an input terminal and an output terminal; washout and lag circuit means having third adder circuit means, first integrator circuit means, fourth adder circuit means and second amplifier circuit means connected in series circuit between said second means for providing a signal representative of longitudinal acceleration and said input terminal of said rate limited lag circuit means; said rate limited lag circuit having fifth adder circuit means, second limiter circuit means, third amplifier circuit means, and second integrator circuit means coupled in series circuit between said input and output terminals thereof; said output terminal of said rate limited lag circuit means coupled to said second input terminal of said second adder circuit means; second filter circuit means having an input terminal and an output terminal, said input terminal connected to said output terminal of said second adder circuit means; fourth amplifier circuit means coupled between said output terminal of said second filter circuit means and said second input terminal of said first adder circuit means; sixth adder circuit means having first and second input terminals and an output terminal; third integrator circuit means having an input terminal and an output termial; seventh adder circuit means having first and second input terminals and an output terminal; said input terminal of said third integrator circuit means coupled to said output terminal of said sixth adder circuit means, said output terminal of said integrator circuit means coupled to said first input terminal of said seventh adder circuit means; servo and throttle means coupled in series between the output of said seventh adder circuit means and the propulsion means for the aircraft; synchronizing amplifier means having an input terminal and an output terminal, said input terminal coupled to the output terminal of said seventh adder circuit means; tachometer means having an input terminal coupled to the output of said servo means, and an output terminal coupled to said second input terminal of said sixth adder circuit means; and switching means coupling said first input terminal of said sixth adder circuit means to said output terminal of said first adder circuit means or to said output terminal of said synchronizing amplifier means.

Claim 10

The invention according to claim 5 further comprising fifth amplifier circuit means and third filter circuit means coupled in series circuit between said output terminal of said second filter circuit means and said second input terminal of said seventh adder circuit means.

Claim 11

The invention according to claim 5 wherein said signal representative of air speed error is a function of the flap position of the aircraft.

Claim 12

The invention according to claim 5 further including means for detecting forward and aft positions of said throttle means; autothrottle limit logic circuit means responsive to said detecting means for actuating said switching means.

Claim 13

In combination with an automatic control system for controlling the airspeed of an aircraft relative to a control reference speed and including means responsive to a command signal, an apparatus providing said command signal substantially free from turbulence noise, comprising: first means for receiving, amplitude limiting and filtering a signal representative of airspeed error; second means for receiving, compensating for wind shear, and filtering a signal representative of inertial longitudinal acceleration; third means for amplifying, combining and processing said amplitude limited and filtered airspeed error signal and said wind shear compensated and filtered inertial longitudinal acceleration signal to provide a first component of said command signal; fourth means for amplifying and processing said wind shear compensated and filtered inertial longitudinal acceleration signal to provide a second component of said commanD signal; fifth means for combining said first and second components of said command signal to provide a resultant command signal; said filtering, amplification and processing of signals representative of amplitude limited airspeed error and wind shear compensated inertial longitudinal acceleration tuned to provide cancellation of said first and second command signal components resulting from turbulence induced airspeed error signals and inertial longitudinal acceleration signals.

Claim 14

In combination with an automatic control system for controlling the airspeed of an aircraft relative to a control reference speed and including means responsive to a command signal, an apparatus providing said command signal substantially free from turbulence noise, comprising: first means for receiving, amplitude limiting and filtering a signal representative of airspeed error; second means for receiving, compensating for wind shear, and filtering a signal representative of inertial longitudinal acceleration; third means for amplifying, combining and processing said amplitude limited and filtered airspeed error signal and said wind shear compensated and filtered inertial longitudinal acceleration signal to provide a first component of said command signal; fourth means for amplifying and processing said wind shear compensated and filtered inertial longitudinal acceleration signal to provide a second component of said commanD signal; fifth means for combining said first and second components of said command signal to provide a resultant command signal; said filtering, amplification and processing of signals representative of amplitude limited airspeed error and wind shear compensated inertial longitudinal acceleration tuned to provide cancellation of said first and second command signal components resulting from turbulence induced airspeed error signals and inertial longitudinal acceleration signals.

Claim 15

In combination with an aircraft control system an automatic speed control system employing a throttle servo responsive to signals representative of airspeed error relative to a selectable control reference speed and inertial longitudinal acceleration for reducing said airspeed error to zero: first means for receiving, amplitude limiting and filtering said airspeed error signal; second means for receiving, compensating for wind shear and filtering said inertial longitudinal acceleration signal; third means for processing said amplitude limited and filtered airspeed error signal to provide a first component of the throttle servo command signal resulting in a rate of change of throttle position proportional to said amplitude limited and filtered airspeed error signal; fourth means for processing said wind shear compensated and filtered inertial longitudinal acceleration signal to provide a second component of the throttle servo command signal resulting in a rate of change of throttle position proportional to said wind shear compensated and filtered inertial longitudinal acceleration signal; fifth means for processing said wind shear compensated and filtered inertial longitudinal acceleration signal to provide a third component of the throttle servo command signal resulting in a change in throttle position proportional to said wind shear compensated and filtered inertial longitudinal acceleration signal; and sixth means for combining said first, second, and third component of the throttle servo command signal to provide a resultant throttle servo command signal.

Claim 16

In combination with an aircraft control system an automatic speed control system employing a throttle servo responsive to signals representative of airspeed error relative to a selectable control reference speed and inertial longitudinal acceleration for reducing said airspeed error to zero: first means for receiving, amplitude limiting and filtering said airspeed error signal; second means for receiving, compensating for wind shear and filtering said inertial longitudinal acceleration signal; third means for processing said amplitude limited and filtered airspeed error signal to provide a first component of the throttle servo command signal resulting in a rate of change of throttle position proportional to said amplitude limited and filtered airspeed error signal; fourth means for processing said wind shear compensated and filtered inertial longitudinal acceleration signal to provide a second component of the throttle servo command signal resulting in a rate of change of throttle position proportional to said wind shear compensated and filtered inertial longitudinal acceleration signal; fifth means for processing said wind shear compensated and filtered inertial longitudinal acceleration signal to provide a third component of the throttle servo command signal resulting in a change in throttle position proportional to said wind shear compensated and filtered inertial longitudinal acceleration signal; and sixth means for combining said first, second, and third component of the throttle servo command signal to provide a resultant throttle servo command signal.

Claim 17

The combination according to claim 10 wherein said amplitude limiting means is selected to provide airspeed control with a transient acceleration limit of about 1 kt/second.

Claim 18

The combination according to claim 10 wherein said filtering and processing for said first, second, and third components of the throttle servo command signal are tuned to provide mutual cancellation of said components when said components result from turbulence induced airspeed error and inertial longitudinal acceleration signals.

Claim 19

In combination with an aircraft control system, an automatic speed control system having a throttle servo responsive to a throttle position command signal, comprising: first means for receiving, amplitude limiting and filtering a signal representative of airspeed error relative to a selectable command speed; second means for receiving, compensating for wind shear and filtering a signal representative of inertial longitudinal acceleration; third means for amplifying, combining and integrating said amplitude limited and filtered airspeed error signal and said wind shear compensated and filtered inertial longitudinal acceleration signal to provide a first component of said throttle position command signal; fourth means for amplifying and further filtering said wind shear compensated and filtered inertial longitudinal acceleration signal to provide a second component of said throttle position command signal; fifth means for combining said signals representative of said first and second component of the throttle position command signal to provide a resultant throttle position command signal for coupling to said throttle servo.

Claim 20

In combination with an aircraft control system, an automatic speed control system having a throttle servo responsive to a throttle position command signal, comprising: first means for receiving, amplitude limiting and filtering a signal representative of airspeed error relative to a selectable command speed; second means for receiving, compensating for wind shear and filtering a signal representative of inertial longitudinal acceleration; third means for amplifying, combining and integrating said amplitude limited and filtered airspeed error signal and said wind shear compensated and filtered inertial longitudinal acceleration signal to provide a first component of said throttle position command signal; fourth means for amplifying and further filtering said wind shear compensated and filtered inertial longitudinal acceleration signal to provide a second component of said throttle position command signal; fifth means for combining said signals representative of said first and second component of the throttle position command signal to provide a resultant throttle position command signal for coupling to said throttle servo.

Claim 21

The combination of claim 13, wherein said throttle servo utilizes a throttle rate signal feedback coupled to said integrating means to provide a signal component representative of change in throttle position.

Claim 22

ThE combination of claim 13 wherein said means for compensating said inertial longitudinal acceleration signal for wind shear comprises: a washout-lag circuit responsive to signals representative of airspeed error and inertial longitudinal acceleration and providing at the output thereof a signal representative of the difference between the lagged inertial longitudinal acceleration and the lagged rate of change of the airspeed error, said output signal representing the rate of change of the velocity of the air relative to the earth; a rate limited lag circuit coupled in series with the output of said washout-lag circuit for providing a wind shear compensation signal representative of the sustained rate of change of the velocity of the air relative to the earth and substantially free from turbulence noise; and means for subtracting said wind shear compensation signal representative of the sustained rate of change of the velocity of the air relative to the earth from said inertial longitudinal acceleration signal to provide wind shear compensated inertial longitudinal acceleration signal.

Claim 23

The combination of claim 15 wherein said washout-lag circuit has a time constant in the order of 0.2 seconds, the rate-limited-lag circuit has a loop gain in the order of 0.2 and a rate limit allowing a maximum rate of change of the output of said rate limited lag circuit in the order of (0.2 knot/second)/second.

Claim 24

The combination according to claim 13 wherein said filtering and amplifying of signals representative of amplitude limited airspeed error and wind shear compensated inertial longitudinal acceleration are tuned to provide mutual cancellation of said first and second throttle position command signal components when said components result from turbulence induced airspeed error and inertial longitudinal acceleration signals.

Claim 25

The combination of claim 13 wherein said airspeed error filter time constant is in the order of 0.5 second, the time constant of said filter coupled in series with said means providing the wind shear compensated inertial longitudinal acceleration signal is in the order of 0.8 second and wherein the time constant of said further filter for said wind shear compensated and filtered inertial longitudinal acceleration signal in the throttle displacement control path is in the order of 0.5 second.

Claim 26

An automatic speed control system comprising in combination: integrator circuit means having an input terminal and an output terminal; first summing circuit means for providing the gain weighted sum of a processed airspeed error signal and a processed airspeed control damping signal, said means having an output terminal; synchronizing amplifier means having an input terminal and an output terminal; switching means having a first input terminal connected to the output of said first summing circuit means, a second input terminal connected to the output terminal of said synchronizing amplifier means and an output terminal; second summing means having a first input connected to the output terminal of said switching means, a second input terminal and an output terminal; integrator circuit means having an input terminal connected to the output terminal of said second summing means and an output terminal; third summing means having a first input terminal connected to said output terminal of said integrator circuit means, a second input terminal receiving a separately processed airspeed control damping signal and an output terminal connected to said input terminal of said synchronizing amplifier means; servo means having an input terminal coupled to the output terminal of said third summing circuit means and an output terminal coupled to the engine throttle levers for driving said throttle levers; switching logic means for switching the connection of said first input signal to said second summing means from the output terminal of said means for providing the gaIn weighted sum of the processed control signals to said output terminal of said synchronizing amplifier means upon reaching either forward or aft throttle limit and for switching back upon a change in sign of said signal representing the gain weighted sum of processed airspeed error and inertial longitudinal acceleration signals; and, means providing a signal representation of the rate of change of throttle lever position for feeding back into said second input terminal of said second summing means.

Claim 27

An automatic speed control system comprising in combination: integrator circuit means having an input terminal and an output terminal; first summing circuit means for providing the gain weighted sum of a processed airspeed error signal and a processed airspeed control damping signal, said means having an output terminal; synchronizing amplifier means having an input terminal and an output terminal; switching means having a first input terminal connected to the output of said first summing circuit means, a second input terminal connected to the output terminal of said synchronizing amplifier means and an output terminal; second summing means having a first input connected to the output terminal of said switching means, a second input terminal and an output terminal; integrator circuit means having an input terminal connected to the output terminal of said second summing means and an output terminal; third summing means having a first input terminal connected to said output terminal of said integrator circuit means, a second input terminal receiving a separately processed airspeed control damping signal and an output terminal connected to said input terminal of said synchronizing amplifier means; servo means having an input terminal coupled to the output terminal of said third summing circuit means and an output terminal coupled to the engine throttle levers for driving said throttle levers; switching logic means for switching the connection of said first input signal to said second summing means from the output terminal of said means for providing the gaIn weighted sum of the processed control signals to said output terminal of said synchronizing amplifier means upon reaching either forward or aft throttle limit and for switching back upon a change in sign of said signal representing the gain weighted sum of processed airspeed error and inertial longitudinal acceleration signals; and, means providing a signal representation of the rate of change of throttle lever position for feeding back into said second input terminal of said second summing means.

Claim 28

In combination in an autothrottle control system for an aircraft: first means for providing a signal representative of airspeed error; second means for providing a signal representative of longitudinal acceleration; first adder circuit means having first and second input terminals and an output terminal; first limiter circuit means; first amplifier circuit means; first filter circuit means; said first limiter circuit means, first amplifier circuit means and first filter circuit means coupled in series circuit between said first means for providing a signal representative of airspeed error and said first input terminal of said first adder circuit means; second adder circuit means having first and second input terminals and an output terminal, said first input terminal coupled to said second means for providing a signal representative of longitudinal acceleration; rate limited lag circuit means having an input terminal and an output terminal; washout and lag circuit means, including third adder circuit means, first integrator circuit means, fourth adder circuit means and second amplifier circuit means, said third adder circuit means having a first input terminal connected to said second means providing a signal representative of longitudinal acceleration and a second input terminal connected in feedback to the output terminal of said second amplifier, said integrator circuit means connected with its input terminal to the output terminal of said third adder circuit means and its output terminal to a first input terminal of said fourth adder circuit means, said fourth adder circuit having a second input terminal connected to said first means providing a signal representative of airspeed error and an output terminal connected to the input terminal of said second amplifier means, said second amplifier means having an output terminal; said rate limited lag circuit including a fifth adder circuit means having a first input terminal connected to said output terminal of said second amplifier means and a second input terminal and an output terminal, a second limiter circuit means having an input terminal connected to said output of said fifth adder circuit means and an output terminal, a third amplifier circuit means having an input terminal connected to said output terminal of said second limiting circuit means and an output terminal, a second integrator circuit means having an input terminal connected to said output terminal of said third amplifier means and an output terminal coupled back to said second input terminal of said fifth adder circuit means, said output terminal of said rate limited lag circuit means also coupled to said second input terminal of said second adder circuit means; second filter circuit means having an input terminal and an output terminal, said input terminal connected to said output terminal of said second adder circuit means; fourth amplifier circuit means coupled between said output terminal of said second filter circuit means and said second input terminal of said first adder circuit means; sixth adder circuit means having first and second input terminals and an output terminal; third integrator circuit means having an input terminal and an output terminal; seventh adder circuit means having first and second input terminals and an output terminal; said input terminal of said third integrator circuit means coupled to said output terminal of said sixth adder circuiT means, said output terminal of said integrator circuit means coupled to said first input terminal of said seventh adder circuit means; throttle servo means coupled in series between the output of said seventh adder circuit means and the propulsion means for the aircraft; synchronizing amplifier means having an input terminal and an output terminal, said input terminal coupled to the output terminal of said seventh adder circuit means; tachometer means having an input terminal coupled to the output of said servo means, and an output terminal coupled to said second input terminal of said sixth adder circuit means; switching means coupling said first input terminal of said sixth adder circuit means to said output terminal of said first adder circuit means or to said output terminal of said synchronizing amplifier means; and, switching logic means for controlling said switching means to couple said output terminal of said synchronizing amplifier to said first input terminal of said sixth adder circuit means when either forward or aft throttle limit is reached, and to couple said output terminal of said first adder circuit means to said first input terminal of said sixth adder circuit means when the sign of the signal present at the output terminal of said first adder circuit changes thereby indicating a servo command to drive the throttle out of its limit position.

Claim 29

In combination in an autothrottle control system for an aircraft: first means for providing a signal representative of airspeed error; second means for providing a signal representative of longitudinal acceleration; first adder circuit means having first and second input terminals and an output terminal; first limiter circuit means; first amplifier circuit means; first filter circuit means; said first limiter circuit means, first amplifier circuit means and first filter circuit means coupled in series circuit between said first means for providing a signal representative of airspeed error and said first input terminal of said first adder circuit means; second adder circuit means having first and second input terminals and an output terminal, said first input terminal coupled to said second means for providing a signal representative of longitudinal acceleration; rate limited lag circuit means having an input terminal and an output terminal; washout and lag circuit means, including third adder circuit means, first integrator circuit means, fourth adder circuit means and second amplifier circuit means, said third adder circuit means having a first input terminal connected to said second means providing a signal representative of longitudinal acceleration and a second input terminal connected in feedback to the output terminal of said second amplifier, said integrator circuit means connected with its input terminal to the output terminal of said third adder circuit means and its output terminal to a first input terminal of said fourth adder circuit means, said fourth adder circuit having a second input terminal connected to said first means providing a signal representative of airspeed error and an output terminal connected to the input terminal of said second amplifier means, said second amplifier means having an output terminal; said rate limited lag circuit including a fifth adder circuit means having a first input terminal connected to said output terminal of said second amplifier means and a second input terminal and an output terminal, a second limiter circuit means having an input terminal connected to said output of said fifth adder circuit means and an output terminal, a third amplifier circuit means having an input terminal connected to said output terminal of said second limiting circuit means and an output terminal, a second integrator circuit means having an input terminal connected to said output terminal of said third amplifier means and an output terminal coupled back to said second input terminal of said fifth adder circuit means, said output terminal of said rate limited lag circuit means also coupled to said second input terminal of said second adder circuit means; second filter circuit means having an input terminal and an output terminal, said input terminal connected to said output terminal of said second adder circuit means; fourth amplifier circuit means coupled between said output terminal of said second filter circuit means and said second input terminal of said first adder circuit means; sixth adder circuit means having first and second input terminals and an output terminal; third integrator circuit means having an input terminal and an output terminal; seventh adder circuit means having first and second input terminals and an output terminal; said input terminal of said third integrator circuit means coupled to said output terminal of said sixth adder circuiT means, said output terminal of said integrator circuit means coupled to said first input terminal of said seventh adder circuit means; throttle servo means coupled in series between the output of said seventh adder circuit means and the propulsion means for the aircraft; synchronizing amplifier means having an input terminal and an output terminal, said input terminal coupled to the output terminal of said seventh adder circuit means; tachometer means having an input terminal coupled to the output of said servo means, and an output terminal coupled to said second input terminal of said sixth adder circuit means; switching means coupling said first input terminal of said sixth adder circuit means to said output terminal of said first adder circuit means or to said output terminal of said synchronizing amplifier means; and, switching logic means for controlling said switching means to couple said output terminal of said synchronizing amplifier to said first input terminal of said sixth adder circuit means when either forward or aft throttle limit is reached, and to couple said output terminal of said first adder circuit means to said first input terminal of said sixth adder circuit means when the sign of the signal present at the output terminal of said first adder circuit changes thereby indicating a servo command to drive the throttle out of its limit position.