(3)
When the EPR pushbutton is operated, the autothrottle system uses engine pressure ratio related signals generated in the performance data computer to compare engine thrust for the particular mode selected and to position the thrust levers to the corresponding thrust settings.
(4)
When the SPEED pushbutton is operated, the autothrottle system is used to control thrust lever position to maintain airspeed as selected by the IAS/MACH speed control.
(5)
The level change (LVL CHG) pushbutton is operated when the autothrottle system is used to control thrust lever position during climb or descent from one altitude to another. The altitude level is as selected by the ALTITUDE SEL control on the AFCS control panel.
(6)
The changeover (C/O) control changes the IAS/MACH display from indicated airspeed to mach number and vice versa. It is not directly associated with the autothrottle system.
(7)
When the V NAV/PDC pushbutton is operated, output data from the performance data computer is applied to the autothrottle computer.
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7. Autothrottle Disengage Switches
A. Each thrust lever has an autothrottle disengage switch in the outboard end of the thrust lever handle. The disengage switches are wired in series and form part of the A/T engage interlock circuits. Pressing either one of the switches causes the autothrottle system to disengage and causes the disengage lights to flash. Pressing the switch a second time resets the disengage lights.
8. AFCS Flight Mode Annunciator (FMA) Panels
A. A flight mode annunciator panel is located on the captain's and first officer's main instrument panels. Each FMA panel has four vertical columns of annunciators: two for the A/P-F/D system and one each for the A/T and PDC systems. Each panel is also provided with two warning lights: one each for the A/P and A/T systems, and a three-position TEST switch.
B. Each individual mode annunciator display consists of a three-faced prism and two prism-driving solenoids. Two faces of the prism are engraved with an annunciator legend; the third face, which is blank, rests in the display position when the prism is deactivated. Each solenoid is energized by separate mode signals (dc ground). When a mode signal is received, the solenoid drives the prism 120 degrees in the required direction to display the corresponding mode legend. When the mode signal is removed, the prism rotates to its blank position. Each prism is illuminated constantly by background lights.
C. When the TEST switch is set to position 1 or 2, each prism on the FMA panel is driven to display either the upper or lower legend, depending on the position selected.
D. The A/T annunciators display the following legends proceeding from top to bottom:
(1)
ARM or blank
(2)
blank or PDC SPEED
(3)
SPEED or EPR
(4)
THR HOLD or RETARD
E. The PDC annunciators, some of which also indicate autothrottle/PDC operational modes, display the following legends, proceeding from top to bottom:
(1)
CON or TURB
(2)
HOLD or CRZ
(3)
DES or CLB
(4)
GA or TO
F. The A/T warning lights flash red after either an automatic or manual disengagement of the autothrottle system. The lights are reset by pressing either the A/T disengage switch or the warning light. The warning lights illuminate steadily red during the BITE operation.
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9. Attitude Director Indicators (ADI)
A. A fast-slow indicator on the captain's and first officer's attitude director indicators provides a visual indication of the difference between programmed airspeed and actual airspeed. The indicator consists of a center-zero vertical scale, and a needle pointer. When the needle is above zero reference, airplane speed is faster than computed airspeed. Conversely, when the needle is below zero reference, airplane speed is slower than computed speed. Fast-slow command signals for each ADI are generated in the autothrottle computer.
10. Angle of Airflow (ALPHA) Vane
A. The angle of airflow vane is installed on the left side of the airplane fuselage at the nose of the airplane. It provides a synchro signal output of ALPHA angle (angle of attack). The output from the left angle of airflow vane is used by the autothrottle system in minimum speed computations. Angle of attack is also used for the V2 and V2+10 knot speed references provided to the ADI pitch command bar for use during takeoff and go-around when the Flight Director System is in SC mode. The vanes are heated during flight to prevent ice buildup.
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