(c)
The ILS glide slope deviation signal is gain programmed with radio altitude and complementary filtered with an altitude rate error signal to form a displacement signal for the beam. Complementary filtered altitude rate feedback is obtained from DADC altitude rate and normal accelerometer to form the path damping signal. Airplane short period damping is provided by a complementary filtered normal acceleration and derived pitch rate feedback signal. Airplane flap changes, thrust and windshear effects cause changes to groundspeed which varies the rate of descent to main beam tracking. Speed compensation is provided which combines the integral of pitch attitude compensated longitudinal acceleration with a pseudobeam displacement rate signal.
(d)
The glide slope control is gain scheduled with airspeed provided by the DADC to compensate for increased elevator effectiveness at high capture speeds.
(e)
A stabilizer trim "negator" circuit provides a signal to the pitch integrator whenever the stab trim drives. This command moves the elevators toward neutral as the stabilizer drives to minimize beam deviation due to trim action.
(f)
When both LOC and G/S modes have been engaged, the APP mode cannot be deselected except by go-around or autopilot disengagement or CWS Hi Detent override. An extinguished APP mode pushbutton light indicates this point in the approach.
(g)
Pressing the go-around switch during a single channel approach with one or both flight directors OFF will cause the autopilot to disengage and approach mode to reset. Flight director go-around will occur if both flight directors are ON and preconditions are met.
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K. Dual Channel A/P Approach
(1)
The AFCS has automatic landing capabilities to CAT IIIA Lower Weather Minimums (LWM). The autoland system is comprised of two independent roll and pitch control channels. When coupled to an ILS, automatic control of the airplane including automatic flare to touchdown may be performed in the dual channel configuration.
(2)
In the dual mode, fail passive control response is provided since a failure response in one channel is immediately counteracted and cancelled by the second channel. If this occurs or in the event of any system failures, dual redundant monitors disconnect the autopilot and provide an aural and visual warning.
(3)
Confidence testing of critical circuitry and the monitoring system is performed automatically at the beginning of an approach. Test success is annunciated and test failure results in either an automatic autopilot disconnect or no FLARE ARM annunciation.
(4)
Additional protection for flare failure effects at low altitudes is provided by a trim bias input at 400 feet. This feature is termed a "flare spring" because it provides a pitch arm maneuver in the event of an autopilot disconnect due to failures.
(5)
Automatic go-around capability is also implemented for dual channel operation. This mode may be selected at any time after the monitors are enabled to abort an approach.
(6)
Below 800 feet in the APP mode and when monitors are active the A/P Disengage Warning lights are used as additional stab out-of-trim annunciators.
(7)
Dual Channel Localizer and Glide Slope Arm (Precapture ILS)
(a) The precapture phase of an autoland is basically the same as described for single channel except that after the selection of APP mode, the second autopilot engage paddle is lifted to the CMD position. The second autopilot channel is only armed as indicated by the SINGLE CH annunciation on the FMA. 中國航空網 www.k6050.com 航空翻譯 www.aviation.cn 本文鏈接地址：737 AMM 飛機維護手冊 AUTO FLIGHT 自動飛行 1(70)
