(c)
The take off power setting is achieved before 60 knots. At 64 knots, two independent circuits ensure that the autothrottle cannot move the thrust levers. A THR HOLD indication displays on the FMA when both circuits have operated.
(d)
At lift off, timers start which normally cause the thrust lever hold circuits to be disabled after 17.5 seconds. If 400 feet has not been reached, an additional circuit prevents the throttle hold from being disabled. This ensures that if an engine fails and the initial climb is prolonged, the thrust levers will not move until 400 feet has been reached.
(2)
EPR Climb Operation
(a)
In addition to EPR control operation in the take off mode, the autothrottle will control EPR in climb. When the autothrottle is engaged in this mode, the autothrottle will control to the climb thrust value or to the engaged PDC value. The FMA will show EPR and the EPR pushbutton on the AFCS control panel will be illuminated. The illuminated pushbutton indicates to the pilot that pressing it will cause the autothrottle to revert to ARM. The maximum thrust lever rate of movement in this mode is limited to three degrees per second.
(b)
During EPR control, if an engine failure occurs, the thrust lever associated with the failed engine will drive forward to attempt to increase EPR. The thrust lever of the failed engine will not be commanded to go more than eight degrees forward of the thrust lever of the remaining normal operating engine.*[1]
(3)
Speed Control Operation
(a)
Speed control is available throughout the entire flight envelope once the take off is completed. With the autothrottle engaged, operating the SPEED pushbutton switch on the AFCS control panel causes the thrust levers to move to control speed if this is compatible with the currently engaged AFCS pitch mode. Selection of the desired speed is accomplished on the AFCS control panel. The lowest selectable Mach is .6 and the lowest selectable airspeed is 110 Kts. The highest selectable speed is MMO = .84 (FAA certification - .82 for CAA) and VMO equivalent to 350 Kts EAS. A changeover (C/O) switch is provided for switching between Mach and airspeed. Automatic C/O occurs at approximately 23,750 feet from CAS to Mach in climb and from Mach to CAS in descent.
(b)
The Flight Mode Annunciator shows SPEED and the AFCS speed pushbutton switch is illuminated during speed or Mach control operation. The switch is illuminated to indicate to the pilot that pressing it will cause the autothrottle to revert to ARM.
(c)
For engine-out operation in the speed control mode, the thrust levers will both advance together to maintain airspeed. The autothrottle will drive the thrust lever on the failed engine until it is eight degrees forward of the thrust lever of the remaining normal operating engine thrust lever.*[1]
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*[1] The difference (in degrees) between the two thrust levers varies inversely with thrust lever rate of movement. A maximum difference of 10 degrees may occur before autothrottle disengagement with minimum rate of movement.
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(d) Speed control law configuration and gains are changed depending on conditions to one of three configurations: approach, capture, or track. 1) Approach Configuration The autothrottle becomes more responsive during approach phase. This is determined by either glideslope capture or by radio altitude and flap angle. During approach, the autothrottle provides an improved response for more precise speed control, and reduced thrust lever motion during flap changes. This tends to cause the autothrottle to be somewhat high on speed during a turbulent approach. The degree of overspeed depends on the magnitude and frequency of the turbulence present. 2) Capture Configuration The capture phase is used when not in the approach configuration and the airplane is in a maneuvering configuration. A maneuvering configuration is defined as: The airplane being lower than 15,000 feet of altitude (and not on track), not in autopilot altitude hold, EPR not valid, off selected speed by five knots, thrust levers at forward or aft limit, flaps being moved, speed selection changed, or the airplane path being changed. Autothrottle capture phase remains active for 60 seconds after activating criteria have disappeared.
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