needed to maintain the required air extraction for anti-icing. Approach idle power control is active only when anti-ice is ON and TAT is less than 10 degrees celsius.
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EPR OR THR AS INSTALLED
MODE CONTROL PANEL
. A/T ARM
. VNAV SELECTED ATTITUDE DIRECTOR INDICATION
. FAST/SLOW OPERATIVE
. IDLE AND THEN THR-HOLD ANNUNCIATED
UPPER EICAS DISPLAY
AIRPLANES WITH STANDARD FORMAT FAST/SLOW DISPLAY AIRPLANES WITH SPEED TAPE DISPLAY AIRPLANES WITH EURO FORMAT FAST/SLOW DISPLAY
Autothrottle - Idle Mode
Figure 18
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M21498
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(f)
(g)
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2) The maximum EPR override logic limits the maximum EPR to the REF EPR value. The MAX EPR rate command used to control actual EPR to the EPR REF is compared to the throttle rate COMMAND. Override occurs if the throttle rate COMMAND is greater (more positive) than the MAX EPR rate command.
3) The aft PLA limit restricts aft travel of the power lever angle (PLA). The PLA aft limits are according to: a) The flight idle limit with flaps retracted b) The ground idle limit with flaps extended c) The flare limit when the flare mode is engaged
4) If the throttle rate COMMAND is greater (more negative) than the aft PLA limit rate command, control switches to the aft PLA limit.
5) The MAX PLA limit restricts forward travel of the power lever angle. The PLA maximum limit is the takeoff limit below 14,000 ft., and Mach and climb limits above 14,000 ft. If the throttle rate COMMAND is greater (more positive) than the MAX PLA rate command, control switches to the MAX PLA limit.
Throttle Servo Rate Command Filter
1) The throttle rate COMMAND is compared to the servo tach feedback. The difference is filtered to form the THROTTLE SERVO RATE COMMAND.
Power Amplifier
1) The THROTTLE SERVO RATE CMD is converted to an analog signal and amplified to drive the variable phase motor in the A/T servomotor generator. The rate command is compared to the tachometer feedback in order to reach the desired rate.
Flight Level Change (FLCH) Control
1) The FLCH control law drives the thrust levers smoothly to the limit (maximum or idle), where they stay until the altitude is captured. The forward thrust limit is the reference thrust target. The aft limit is the throttle aft mechanical stop.
2) The actual PLA rate is compared to the command rate. If a difference is detected, pilot override is assumed to have occurred and FLCH hold is engaged. This removes the rate command and the excitation from the A/T servomotor generator.
Power Lever Angle Retard Control
1) The PLA aft limits differ depending on the flight conditions: a) Flare retard - 48 degrees (flare idle)
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b) Landing flaps - 57.4 degrees (flight idle)
c) Ground idle - 53 degrees
2) The enable servo control signal from the retard logic switches control to the aft PLA limit. Upon reaching the aft limit, the autothrottle servo is placed in hold until a throttle advance is commanded.
(19)
Autothrottle Speed Mode (Fig. 19)
(a)
The speed mode is engaged when the A/T arm switch is in the ARM position and the MCP SPD request is valid. Automatic speed mode engage occurs when the VNAV or FLCH mode is exited.
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