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MAINTENANCE MANUAL
SELECT SWITCH/LIGHT
. GLIDE SLOPE ARMED . G/S CAPTURED . APP SWITCH PRESSED . CAP CRITERIA
-APP SWITCH DOT-BAR BASED ON
ILLUMINATED - DISTANCE FROM GLIDE PATH
-FMA ON EADI INDICATES - RATE OF APPROACH TO GLIDE PATH
G/A ARMED . FMA ON EADI INDICATES G/S . POSSIBLE ACTIVE MODES IN PITCH MODE ENGAGED SECTION
-VNAV
-V/S
- FLCH
D
-ALT HOLD
Pitch Channel - Approach Mode (Glide slope)
Figure 15 (Sheet 2)
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(19) Approach Control Signal Flow and Monitoring
(a) Signal Selection
1) The vertical position approach logic selects filtered glideslope deviation altitude and filtered glideslope deviation rate inputs to command processing. Since the deviation altitude is the distance from the main landing gear to the glideslope beam centerline, a bias of 19 feet is added to reference it to the glideslope antenna.
2) The vertical position approach logic selects the gains for glideslope operation. The position and rate errors are combined to form the integral and proportional commands.
(b)
Acceleration Forecast
1) At glideslope capture, the capture region is determined by the relationship between deviation altitude and deviation rate. If no acceleration limit is required, the output is a no acceleration limit region computation pulse. If some acceleration limit is required, acceleration limit region computation latch is set. This is reset when exceeding the acceleration limit is no longer forecast. The overshoot limit region computation latch is set if overshoot is forecast. When the airplane is parallel to the glideslope beam centerline, overshoot limit region computation is reset.
(c)
Vertical Acceleration Command Limit
1) When a limit is imposed, the acceleration commanded by the command processor will be set at this value. For glideslope it is a fixed value of 2.5 ft/sec/sec.
2) If no acceleration limits are imposed, the natural frequency sets the gains in the second order filter. The commanded deviation and rate decay from the initial values at a time constant set by the natural frequency.
3) If acceleration limits are imposed, vertical position limit logic operates and the commanded rate is reduced at the fixed 2.5 ft/sec/sec acceleration limit. When the limit is removed, the commanded position and rate decay to zero with the calculated time constant.
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4) Vertical position error and vertical position rate error are the differences between commanded and actual position and rate respectively.
(20)
Pitch Channel - Go-Around Mode (Fig. 16)
(a)
Transition to Go-Around mode is possible from all modes except control inactive and takeoff. Go-around mode can exit into all modes except takeoff and glideslope. The VNAV ARM submode is permissible for go-around. A valid go-around switch request is required to enter go-around mode.
(b)
On entry into go-around mode the elevators are commanded to capture and hold selected airspeed and the autothrottle (if engaged) commands a 2000 FPM climb rate. A pitch up signal to the elevators is provided to compensate for the increased thrust. The flight mode annunciator on the EADI displays GA as the go-around mode is engaged.
(21)
Pitch Channel - Autoland (Fig. 17)
(a)
Multichannel engage is initiated when one channel is engaged in CMD and one or more A/P channels are manually placed in CMD with APP selected. The switches remain in CMD only if APP is selected. The Autoland Status Annunciator (ASA) shows autoland capability (Ref 22-14-00).
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