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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL
(17)
Pitch Channel - Approach (Glideslope) (Fig. 15)
(a)
The approach mode is armed by pressing the APP switch/light. This also arms the glideslope. Glideslope will engage when the glideslope capture criteria are satisfied. Command engage configuration can be single channel or multi-channel. glideslope is a valid submode in single or multi-channel engage. Flare is a valid submode in multi-channel engage only.
(b)
Manual entry from any permissible mode is possible when the APP switch/light dot bar matrix is lighted. If the switch/light is pressed again, prior to LOC or G/S capture, the APP mode is disarmed.
(c)
Automatic exit from the APP mode can occur three ways: selecting a different roll mode after LOC capture but prior to glideslope capture; selecting a different pitch mode after glideslope capture but before LOC capture; and when go-around is selected. There is a one-sampling time interruption of the APP mode if only the F/D is engaged and one channel is initially engaged in CMD.
(d)
Two submodes are permissible in APP ARM: glideslope ARM and glideslope engaged. The flight mode annunciator on the EADI shows G/S (glideslope) as the pitch mode armed and pitch mode engaged respectively.
(18)
Glideslope Command Logic
(a) Glideslope Capture
1) Glideslope capture is armed by APP mode ARM. A bias is added to gear deviation altitude to reference the deviation back to the glide slope antenna. When deviation and rate meet the capture criteria and the airplane is approaching the beam, a capture signal is generated.
2) If deviation and rate reach minimum values without capture criteria being met, capture is forced by a second capture signal. The glideslope engage logic is latched until APP ARM is removed, or Flare is engaged, or until the airplane is on the ground.
(b) Vertical Position Logic
1) The vertical position engage logic goes invalid for one iteration after a vertical position mode change. This allows synchronization to new values. Vertical position engage transition logic goes valid for one frame during the next iteration time. This logic is used by acceleration forecast circuits for acceleration limit determination. One time frame later, vertical position engage delayed logic becomes valid and enables the acceleration limit reset.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757 MAINTENANCE MANUAL
FLIGHT CAPTAIN'S COMMAND ENGAGE (CMD) LEFT, CENTER, RIGHT SWITCH/LIGHT AUTOPILOT
. 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
B
-FLCH
-ALT HOLD
Pitch Channel - Approach Mode (Glide Slope)
Figure 15 (Sheet 1)
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