초록 ▼

An integrated aircraft longitudinal flight control system uses a generalized thrust and elevator command computation (38), which accepts flight path angle, longitudinal acceleration command signals, along with associated feedback signals, to form energy rate error (20) and energy rate distribution e

An integrated aircraft longitudinal flight control system uses a generalized thrust and elevator command computation (38), which accepts flight path angle, longitudinal acceleration command signals, along with associated feedback signals, to form energy rate error (20) and energy rate distribution error (18) signals. The engine thrust command is developed (22) as a function of the energy rate distribution error and the elevator position command is developed (26) as a function of the energy distribution error. For any vertical flight path and speed mode the outerloop errors are normalized (30, 34) to produce flight path angle and longitudinal acceleration commands. The system provides decoupled flight path and speed control for all control modes previously provided by the longitudinal autopilot, autothrottle and flight management systems.

대표청구항 ▼

1. An aircraft longitudinal flight control system for automatically controlling the aircraft's flight path and speed, using engine thrust and elevator control surface position, comprising: means for developing an incremental net thrust command signal ΔT c which is a linear combination of a signal

1. An aircraft longitudinal flight control system for automatically controlling the aircraft's flight path and speed, using engine thrust and elevator control surface position, comprising: means for developing an incremental net thrust command signal ΔT c which is a linear combination of a signal representative of the aircraft's total energy error with respect to the flight path and speed command targets and a signal representative of the rate of change of the aircraft's total energy; thrust control means for automatically controlling the incremental net thrust of the engines to said incremental net thrust command signal ΔT c, such that said total energy error is reduced to zero; means for developing an incremental elevator position command Δδ e .sbsb.c for controlling the deviation of the aircraft from a commanded flight path; and elevator position control means for automatically positioning the elevator to said incremental elevator command signal Δδ e .sbsb.c such that said deviation of the aircraft from the commanded flight path is reduced to zero. 2. An aircraft longitudinal flight control system for automatically controlling the aircraft's flight path and speed using engine thrust and elevator control surface position, comprising: means for developing an incremental thrust command signal ΔT c which is a linear combination of a signal representative of the aircraft's total energy error with respect to the flight path and speed command targets and a signal representative of the rate of change of the aircraft's total energy; thrust control means for automatically controlling the incremental thrust to said incremental thrust command signal ΔT c such that said total energy error is reduced to zero; means for developing an incremental elevator command signal Δδ e .sbsb.c which is a linear combination of a signal representative of the aircraft's total energy distribution error with respect to the flight path and speed targets, a signal representative of the rate of change of the total energy distribution, and pitch control damping signals; and elevator position control means for automatically controlling the incremental elevator position to said incremental elevator command signal Δδ e .sbsb.c such that said aircraft's total energy distribution error is reduced to zero. 3. An automatic flight control system for controlling an aircraft's vertical flight path and speed, comprising: means for developing a flight path angle command signal γ c for guiding the aircraft to, or holding the aircraft on, a desired vertical flight path; means for developing a longitudinal acceleration command signal V c for guiding the aircraft to, or holding the aircraft on, a desired speed; means for providing signals representative of the aircraft's vertical flight path angle γ and longitudinal acceleration V; means for simultaneously processing said γ c, γ and said V c, V signals to produce an incremental net thrust command signal ΔT c and an incremental elevator command signal Δδ e .sbsb.c, said ΔT c and Δδ e .sbsb.c signals being related to the aircraft's total energy error and total energy distribution error, respectively, with respect to the flight path and speed command targets, and said ΔT c and Δδ e .sbsb.c signals coordinated in time and in magnitude to provide decoupled vertical flight path and speed command control; means for receiving the incremental thrust command signal ΔT c and controlling the net thrust of the engines in response thereto; and means for receiving the incremental elevator command signal Δδ e .sbsb.c and controlling the elevator position in response thereto. 4. An automatic flight control system for controlling the aircraft's vertical flight path and speed, comprising: means for developing a flight path angle command signal γ c for guiding the aircraft to, or holding the aircraft on, a desired flight path; means for developing a longitudinal acceleration command signal V c for guiding the aircraft to, or holding the aircraft on, a desired speed; means for providing signals representative of the aircraft's vertical flight path angle γ and longitudinal acceleration V; means for developing a signal E s .sbsb.ε representative of the specific total energy rate error, where E s .sbsb.ε =(γ c -γ)+(V c -V)/g and a signal D ε representative of the energy rate distribution error where D ε =-(γ c -γ)+(V c -V)/g; automatic thrust control means for controlling the net thrust in linear proportion to the time integral of said E s .sbsb.ε signal; automatic elevator position control means controlling the elevator position in linear proportion to the time integral of said D ε signal; said simultaneous thrust and elevator control causing the flight path and speed to track the commanded flight path and speed. 5. An automatic flight control system for controlling an aircraft's vertical flight path and speed, comprising: means for developing a flight path angle command signal γ c and a longitudinal acceleration command signal V c for guiding the aircraft to, or holding the aircraft on, a desired flight path and speed; means for providing signals representative of the aircraft's flight path angle γ and longitudinal acceleration V; means for developing an incremental thrust command signal ΔT c by forming a linear combination of the time integral of the aircraft's specific total energy rate error signal E s .sbsb.ε, where E s .sbsb.ε =(γ c -γ)+(V c -V)/g and the specific total energy rate signal E s, where E s =γ+V/g: ##EQU## and means for developing an incremental elevator position command signal Δδ e .sbsb.c, by forming a linear combination of the time integral of the aircraft's energy rate distribution error signal D ε, where D ε =-(γ c -γ)+(V c -V)/g and the energy rate distribution signal D, where D=-γ+V/g: ##EQU## thrust control means for coupling said incremental thrust command signal ΔT c to the engine and controlling the thrust thereto; and elevator position control means for coupling said incremental elevator command signal Δδ e .sbsb.c to the elevator and controlling the position thereto. 6. The system of any one of the claims 3 or 5 wherein said incremental thrust command signal ΔT c is scaled in proportion to aircraft weight. 7. The system of claim 6 in which said means for developing the incremental elevator command signal includes: means for providing and processing aircraft pitch control damping signals such as pitch rate θ and pitch attitude θ or vertical acceleration h to produce a pitch damping signal; and means for combining said pitch damping signal with said incremental elevator command signal producing a total elevator command signal, yielding energy distribution control with pitch damping when coupled to said elevator control system. 8. The system of claim 7 wherein said means for developing the flight path angle command signal γ c comprises: means responsive to pilot manipulation for selecting the desired flight path angle command and providing a representative signal output thereof. 9. The system of claim 8 wherein said means for developing the flight path angle command signal γ c, comprises: means for providing a signal representative of the force exerted by the pilot on the aircraft control column; means for processing said column force signal through a dead zone circuit; means for scaling the output from said dead zone circuit inversely proportional to a signal representative of airspeed or inertially smoothed airspeed to provide a signal γ c representative of the rate of change of the flight path angle command; and means for lag filtering and integrating said γ c signal to provide said flight path angle command signal γ c for the velocity vector control wheel steering mode. 10. The system of claim 7 wherein said means for developing the flight path angle command signal γ c ; comprises: means for providing a signal representative of the force exerted by the pilot on the aircraft control column; means for processing said column force signal through a dead zone circuit; means for scaling the output from said dead zone circuit inversely proportional to a signal representative of airspeed or inertially smoothed airspeed to provide a signal γ c representative of the rate of change of the flight path angle command; and means for lag filtering and integrating said γ c signal to provide said flight path angle command signal γ c for the velocity vector control wheel steering mode. 11. The system of claim 6 wherein said means for developing the flight path angle command signal γ c comprises: means responsive to pilot manipulation for selecting the desired flight path angle command and providing a representative signal output thereof. 12. The system of claim 11 wherein said means for developing the flight path angle command signal γ c, comprises: means for providing a signal representative of the force exerted by the pilot on the aircraft control column; means for processing said column force signal through a dead zone circuit; means for scaling the output from said dead zone circuit inversely proportional to a signal representative of airspeed or inertially smoothed airspeed to provide a signal γ c representative of the rate of change of the flight path angle command; and means for lag filtering and integrating said γ c signal to provide said flight path angle command signal γ c for the velocity vector control wheel steering mode. 13. The system of claim 6 wherein said means for developing the flight path angle command signal γ c comprises: means for providing a signal representative of the force exerted by the pilot on the aircraft control column; means for processing said column force signal through a dead zone circuit; means for scaling the output from said dead zone circuit inversely proportional to a signal representative of airspeed or inertially smoothed airspeed to provide a signal γ c representative of the rate of change of the flight path angle command; and means for lag filtering and integrating said γ c signal to provide said flight path angle command signal γ c for the velocity vector control wheel steering mode. 14. The system of claim 6 wherein said means for developing the flight path angle command signal γ c comprises a bias signal selected to provide an optimum climb-out gradient during go-around, said bias signal processed through shaping filter to provide the desired initial dynamics. 15. The system of claim 6 wherein said means for developing the flight path angle command signal γ c comprises: means for developing a vertical speed command signal h c ; means for providing a signal V representative of the aircraft speed; and means for normalization of said h c signal into said γ c signal according to the relationship γ c =h c /V. 16. The system of either one of claims 3 or 5 in which said means for developing the incremental elevator command signal includes: means for providing and processing aircraft pitch control damping signals such as pitch rate θ and pitch attitude θ or vertical acceleration h to produce a pitch damping signal; and means for combining said pitch damping signal with said incremental elevator command signal producing a total elevator command signal, yielding energy distribution control with pitch damping when coupled to said elevator position control means. 17. The system of claim 16 wherein said means for developing the flight path angle command signal γ c comprises: means responsive to pilot manipulation for selecting the desired flight path angle command and providing a representative signal output thereof. 18. The system of claim 17 wherein said means for developing the flight path angle command signal γ c, comprises: means for providing a signal representative of the force exerted by the pilot on the aircraft control column; means for processing said column force signal through a dead zone circuit; means for scaling the output from said dead zone circuit inversely proportional to a signal representative of airspeed or inertially smoothed airspeed to provide a signal γ c representative of the rate of change of the flight path angle command; and means for lag filtering and integrating said γ c signal to provide said flight path angle command signal γ c for the velocity vector control wheel steering mode. 19. The system of claim 16 wherein said means for developing the flight path angle command signal γ c, comprises: means for providing a signal representative of the force exerted by the pilot on the aircraft control column; means for processing said column force signal through a dead zone circuit; means for scaling the output from said dead zone circuit inversely proportional to a signal representative of airspeed or inertially smoothed airspeed to provide a signal γ c representative of the rate of change of the flight path angle command; and means for lag filtering and integrating said γ c signal to provide said flight path angle command signal γ c for the velocity vector control wheel steering mode. 20. The system of claim 16 wherein said means for developing the fight path angle commanded signal γ c comprises a bias signal selected to provide an optimum climb-out gradient during go-around, said bias signal processed through shaping filter to provide the desired initial dynamics. 21. The system of claim 16 wherein said means for developing the flight path angle command signal γ c comprises: means for developing a vertical speed command signal h c ; means for providing a signal V representative of the aircraft speed; and means for normalization of said h c signal into said γ c signal according to the relationship γ c =h c /V. 22. The system of any one of claims 3 through 5 wherein said means for developing the flight path angle command signal γ c comprises: means responsive to pilot manipulation for selecting the desired flight path angle command and providing a representative signal output thereof. 23. The system of claim 22 wherein said means for developing the flight path angle command signal γ c, comprises: means for providing a signal representative of the force exerted by the pilot on the aircraft control column; means for processing said column force signal through a dead zone circuit; means for scaling the output from said dead zone circuit inversely proportional to a signal representative of airspeed or inertially smoothed airspeed to provide a signal γ c representative of the rate of change of the flight path angle command; and means for lag filtering and integrating said γ c signal to provide said flight path angle command signal γ c for the velocity vector control wheel steering mode. 24. The system of any one of claims 3 through 5 wherein said means for developing the flight path angle command signal γ c comprises: means for providing a signal representative of the force exerted by the pilot on the aircraft control column; means for processing said column force signal through a dead zone circuit; means for scaling the output from said dead zone circuit inversely proportional to a signal representative of airspeed or inertially smoothed airspeed to provide a signal γ c representative of the rate of change of the flight path angle command; and means for lag filtering and integrating said γ c signal to provide said flight path angle command signal γ c for the velocity vector control wheel steering mode. 25. The system of claim 24 wherein said γ c signal processing further includes: first γ c amplifying means for providing a rate of change of thrust command signal which is input to the thrust command integrator; second γ c amplifying means for developing a rate of change of elevator command signal which is input to the elevator command integrator; and third γ c amplifying means for developing a pitch rate command signal which is added to the elevator command signal downstream of the elevator command integrator. 26. The system of any one of claims 3 through 5 wherein said means for developing the flight path angle command signal γ c comprises a bias signal selected to provide an optimum climb-out gradient during go-around, said bias signal processed through shaping filter to provide the desired initial dynamics. 27. The system of any one of claims 3 through 5 wherein said means for developing the flight path angle command signal γ c comprises: PG,79 means for developing a vertical speed command signal h c ; means for providing a signal V representative of the aircraft speed; and means for normalization of said h c signal into said c signal according to the relationship γ c =h c /V. 28. The system of claim 27 wherein said aircraft speed signal V represents airspeed or inertially smoothed airspeed. 29. The system of claim 27 in which the means providing said h c signal comprises: means responsive to pilot manipulation for selecting the desired vertical speed and providing a representative signal output thereof. 30. The system of claim 27 in which the means for providing said h c signal comprises: means for providing the altitude deviation signal h ε of the aircraft relative to a desired flight path; and means for normalizing said altitude deviation signal h ε into said h c signal according to the relationship ##EQU##h c =K h h ε wherein K h is a constant, selected to provide suitable h response dynamics. 31. The system of claim 30 in which engagement of the altitude control mode is triggered by the flight path angle error signal γ ε (where γ ε =K h h ε /V-γ) becoming opposite in sign to the commanded flight path angle signal γ c (where γ c =K h h ε /V), indicating a condition in which the aircraft is tangent to the altitude command capture trajectory as represented by the locus of K h h ε /V-γ=0. 32. The system of claim 30 in which the flight path angle error for flying the landing approach glide path is formed according to the relationship: ##EQU## where h ε =the linear deviation of the aircraft from the desired glide path k h =constant providing suitable path capture dynamics V=airspeed or inertially smoothed airspeed, h=aircraft vertical speed, h=aircraft vertical acceleration, τ=filter time constant, and S=Laplace operator. 33. The system of claim 30 in which the flight path angle error for flying a vertical path profile consisting of straight path segments defined by the geographic location and altitude of the end points is formed according to the relationship: ##EQU## where h ε =the linear deviation of the aircraft from the desired flight path, K h =constant selected to provide suitable path capture dynamics, V=airspeed or inertially smoothed airspeed, h=aircraft vertical speed, h=aircraft vertical acceleration, τ=filter time constant, and S=Laplace operator. 34. The system of claim 33 in which said flight path angle error computation is carried out simultaneously for a current leg of the vertical path and a next upcoming leg and whereby reversion of the path control from the current leg to the upcoming leg is triggered by the sign of γ ε computation for the upcoming leg becoming opposite in sign to the incremental flight path angle command signal Δγ c or Δh c where Δγ c =K h .h 68 /V=Δh c /V. 35. The system of claim 27 in which said h c signal is rate limited to a value h MAX, where h MAX is a constant representing the maximum allowable vertical acceleration. 36. The system of claim 35 in which the acceleration command signal V c is rate limited to a value gh MAX /V, where g represents the gravity constant, h MAX represents the maximum allowable vertical acceleration and V represents the aircraft's airspeed or inertially smoothed airspeed, providing energy transfer capability from speed to altitude or vice versa without thrust response. 37. The system of any one of claims 3 through 5 in which said means for providing said γ signal, representative of the aircraft's flight path angle comprises: means for providing a signal h representative of the sinkrate of the aircraft; means for providing a signal representative of the true altitude h R of the aircraft relative to the terrain; means for limiting said h R altitude signal to a value corresponding to the altitude at which the landing flare is to start; means for amplifying said sinkrate signal by a factor τ F, summing it with the h R signal output from said signal limiting means and processing the combined signal through a high pass filter having the transfer function S/(τ F S+1) where S represents the Laplace operator and τ F represents the filter time constant; means for passing said h signal through a switch to a lag filter only when the terrain altitude signal h R is greater than said terrain altitude signal limit, said lag filter having a transfer function 1/(τ F S+1); means for combining the output of said high pass filter and said lag filter to form a derived h signal, which is referenced to the terrain during the flare maneuver; means for providing an inertially smoothed true airspeed signal; and means for dividing said derived h signal by said inertially smoothed true airspeed signal to produce said γ signal. 38. The system of claim 37 further including: means for combining said derived h signal with an h BIAS signal representative of the desired sinkrate at touchdown; means for providing a signal representative of ground speed V G and dividing said V G signal by said inertially smoothed true airspeed signal to form a speed ratio signal; means for amplifying said combined h signal by a gain factor K and multiplying the resulting signal by said speed ratio signal to produce a flare command signal; switching means for replacing the γ ε signal used in developing thrust and elevator commands with said flare command signal at the instant the terrain altitude signal h R drops below said terrain altitude signal limit; and switching means for replacing the V c signal used in developing thrust and elevator commands with a V c -BIAS signal at the instant the terrain altitude signal h R drops below said terrain altitude signal limit to develop coordinated elevator and throttle retard commands for controlling the landing flare maneuver. 39. The system of any one of claims 2 through 5 wherein said means for providing a signal V representative of the longitudinal acceleration signal comprises: means for providing a signal representative of the thrust T; means for providing a signal representative of the aircraft weight W; means for providing a signal representative of the true airspeed V TRUE ; and signal processing means for developing a signal V or V/g representative of the longitudinal acceleration according to the relationship ##EQU## where: g=acceleration due to gravity V TRUE =true airspeed γ=flight path angle T=net thrust W=aircraft weight τ V =filter time constant, and S=Laplace operator. 40. The system of any one of claims 3 through 5 in which said means for developing a longitudinal acceleration command signal V c comprises: means for providing a speed deviation signal V ε of the aircraft relative to the desired speed and means for normalizing said speed deviation signal V ε into the longitudinal acceleration command signal V c, according to the relationship V c =K V V ε where K V is a constant selected to provide suitable speed response dynamics. 41. The system of claim 40 wherein the gains K h and K V are selected equal in magnitude to provide equal weighting of altitude and speed errors in terms of energy. 42. The system of claim 41 wherein said speed deviation signal V ε of the aircraft relative to the desired speed represents deviation in terms of true airspeed. 43. The system of claim 40 in which the means for providing a speed deviation signal V ε includes means for automatically selecting from: (a) a first means providing V E .sbsb.SEL, representing the speed deviation of the aircraft relative to a pilot selected speed command, (b) a second means providing V MIN .sbsb.ε, representing the speed deviation of the aircraft relative to a minimum safe speed, (c) a third means providing V MAX .sbsb.ε representing the speed deviation of the aircraft relative to a maximum safe speed, with said selection governed by: ##EQU##V ε =V MIN .sbsb.ε if V ε .sbsb.SEL ≤V MIN .sbsb.ε ##EQU##V ε =V MAX .sbsb.ε if V ε .sbsb.SEL ≥V MAX .sbsb.ε V ε =V ε .sbsb.SEL if V MAX .sbsb.ε ≤V ε .sbsb.SEL ≤V MIN .sbsb.ε where the error signals V ε, V ε .sbsb.SEL, V MIN .sbsb.ε, V MAX .sbsb.ε are positive if the associated speed command exceeds the actual speed. 44. The system of claim 43 wherein said means for providing V ε .sbsb.SEL comprises: means for providing a signal V CAS representative of the calibrated airspeed of the aircraft; means responsive to pilot manipulation for selecting the desired calibrated airspeed V CAS .sbsb.c and providing a representative signal output thereof; and means for developing the calibrated airspeed error by subtracting said V CAS signal from said V CAS .sbsb.c signal and converting said calibrated airspeed error into a true airspeed error V ε .sbsb.SEL by multiplication with a calibration factor K ALT which is a predetermined function altitude. 45. The system of claim 43 wherein said means for providing V ε .sbsb.SEL comprises: means for providing a MACH number signal representative of the ratio of the true airspeed of the aircraft and the speed of sound; means responsive to pilot manipulation for selecting the desired MACH number command MACH c and providing a signal output representative thereof; means for providing a signal V TRUE representative of the true airspeed of the aircraft; means for developing a signal a representative of the speed of sound by dividing said true airspeed signal V TRUE by said MACH signal; means for converting said MACH c signal into a true airspeed command signal V T .sbsb.c by multiplying said MACH c signal by said speed of sound signal a; and means for developing the true airspeed error signal V ε .sbsb.SEL by subtracting said true airspeed signal V TRUE from said true airspeed command signal V T .sbsb.c. 46. The system of claim 43 wherein said means for providing V MIN comprises: means for developing a signal α MAX representative of the maximum safe angle of attack for the aircraft; means for providing a signal α representative of the actual angle of attack of the aircraft; means for providing a factor K α representative of the ratio of the steady state change in speed per unit change in angle of attack; means for forming the angle of attack error α ε by subtracting said α signal from said α MAX signal and normalizing said α ε signal into an equivalent airspeed error signal V ε .sbsb.α by multiplying it with said factor K α and processing the resulting signal through a low pass filter to provide the long term component of the V MIN .sbsb.ε signal; means for providing a signal V TRUE representative of the true airspeed; means for providing and processing a flap position signal to develop a signal ΔV c representative of the minimum desired speed increment as a function of the aircraft's flap position change; means for combining said V TRUE signal and said ΔV c signal and processing the resulting signal in a high pass filter to provide a short term component of said V MIN .sbsb.ε signal; and means for combining said signals representative of the long term component of V MIN .sbsb.ε and the short term component of V MIN .sbsb.ε to form the total V MIN .sbsb.ε signal representative of the aircraft airspeed deviation relative to the minimum safe speed. 47. The system of claims 3 through 5 wherein said flight path angle command signal γ c is rate limited to a value of h LIMIT /V, where h LIMIT is a constant representing a maximum allowable vertical acceleration and V represents airspeed or inertially smoothed airspeed. 48. The system of any one of claims 3 through 5 in which the acceleration command signal V c is rate limited to a value gh MAX /V, where g represents the gravity constant, h MAX represents the maximum allowable vertical acceleration and V represents the aircraft's airspeed or inertially smoothed airspeed, providing energy transfer capability from speed to altitude or vice versa without thrust response. 49. The system of claim 5 including: means for providing the rated thrust limit of the engine; means for limiting the engine thrust to a predetermined upper limit and developing a FORWARD LIMIT discrete signal when the command thrust reaches the upper thrust limit; means for limiting the engine thrust to a predetermined lower limit value and developing an AFT LIMIT discrete signal when the commanded thrust reaches this lower limit; means for removing the flight path angle error signal γ ε =γ c -γ input to the elevator command computation when either the FORWARD LIMIT or AFT LIMIT discrete signal is true; means for limiting the longitudinal acceleration command signal V c whenever the FORWARD LIMIT discrete signal is true, to a value V c .sbsb.LIM =V-gγ ε or V c .sbsb.LIM =K(V+gγ) whichever is greater and limiting the longitudinal acceleration command signal V c whenever the AFT LIMIT discrete is true, to a value V c .sbsb.LIMIT =V-gγ ε or V c .sbsb.LIM =K 2 (V+gγ) whichever is less, the values of K 1 and K 2 selected between 1.0 and 0 to prioritize either speed or flight path command execution. 50. The system of claim 49 wherein said means for limiting the engine thrust comprises: means for converting the incremental net thrust command signal ΔT c into an incremental variable ΔEPR c (incremental engine pressure ratio command) or ΔN 1 .sbsb.c (incremental fan speed) by which the engine thrust can be controlled readily; means for providing a signal EPR IDLE or N 1 .sbsb.IDLE representative of the engine control variable at idle, means for combining said incremental engine control variable ΔEPR c or N 1 .sbsb.c with said EPR IDLE or N 1 .sbsb.IDLE signal for providing an absolute engine control command signal EPR c or N 1 .sbsb.c ; means for providing a signal EPR LIM or N 1 .sbsb.LIM representative of the maximum allowable value of the engine control variable; means for feeding back the difference between said EPR LIMIT or N 1 .sbsb.LIMIT and said EPR c or N 1 .sbsb.c signal with high gain to the input of the thrust command integrator if said EPR c or N 1 .sbsb.c exceeds said EPR LIMIT or N 1 .sbsb.LIMIT signal, so as to limit the value of EPR c or N 1 .sbsb.c to said EPR LIMIT or N 1 .sbsb.LIMIT ; and means for controlling the engine thrust to make the actual engine pressure ratio EPR or fan speed N 1 track the command signal EPR c or N 1 . 51. The system of claim 50 wherein said means for converting the incremental net thrust command signal ΔT c into an incremental engine control variable ΔEPR c or ΔN 1 comprises: means for providing a signal δ, representative of the ratio of the atmospheric pressure at aircraft altitude and the sea level atmospheric pressure and dividing said ΔT c signal by said δ signal to provide a normalized incremental thrust command signal; means for converting said normalized incremental thrust command signal into the incremental thrust control command signal Δ EPR .sbsb.c (incremental engine pressure ratio) or N 1 (incremental fan speed); and means for controlling the engine thrust so as to make the actual incremental EPR or N 1 track ΔEPR c or ΔN 1 . 52. The system of claim 51 wherein said means for controlling the engine thrust to said ΔEPR c or N 1 .sbsb.c comprises: means for providing the actual engine EPR or N 1 ; means for providing a signal EPR IDLE or N 1 .sbsb.IDLE representative of the value of the engine control variable at idle; means for subtracting said EPR IDLE or N 1 .sbsb.IDLE signal from the sum of said EPR or N 1 signal and said ΔEPR c signal to form an EPR error signal; means for converting said EPR error signal into a trim throttle position command signal; means for converting said ΔEPR c signal into a target throttle position command signal; means for combining said trim throttle position command signal, said target throttle position command signal and an idle bias signal to form a total throttle position command signal; and means for controlling the actual throttle position to said total throttle position command signal.