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A
757 MAINTENANCE MANUAL
ILS DEVIATION MONITOR - DESCRIPTION AND OPERATION
_________________________________________________
1. General (Fig. 1)_______
A. The ILS deviation monitoring system consists of separate glideslope and localizer monitors. The monitors are an integral part of the EFIS symbol generators software. The monitors cause the EADI glideslope and localizer deviation scales to change from white to yellow and the deviation pointers to flash at four hertz. The monitors are enabled when the airplane deviates beyond prescribed limits from the center of the glideslope and localizer beams with the autopilot or flight director in approach mode.
B. An expanded scale with a rising runway is displayed when localizer deviation is less than 5/8 of a dot; localizer or rollout mode is armed, and left, center, and/or right autopilot is engaged. The expanded display reverts back to standard scale if the deviation exceeds one dot, or if both modes are disengaged and ground speed is less than 30 knots or radio altitude is greater than 200 feet.
C. All components used by the ILS deviation monitor are part of the
Electronic Flight Instrument System (EFIS), (Ref 34-22-00).
D. The ILS Deviation Monitor function is an option that is selected by hard wiring to ground the EFIS symbol generator ILS DEV WARN pin.
E. The monitor function is tested during the EFIS system self-test. The self-test is active only when the airplane is on the ground.
2. Operation_________
A. The ILS deviation warning option is available whenever the ILS DEV WARN pin (E8 on connector insert B) on the EFIS symbol generators is grounded.
B. The ILS deviation warning is armed when the following conditions also exist:
(1)
EFIS symbol generator autopilot mode status input is set to logic one (Approach Mode Engaged).
(2)
Radio Altitude between 500 and 100 feet for glideslope.
(3)
Radio Altitude between 500 feet and touchdown for localizer.
C. The ILS Deviation warning is issued when the above conditions exist and either or both of the following deviations exist for one second (Fig. 1, Part A).
(1)
Glideslope deviation pointer is greater than .87 dot above or below the glideslope beam center.
(2)
Localizer deviation pointer is greater than .27 dot left or right of the localizer beam center.
D. The EFIS symbol generator changes the white deviation scale for either the EADI glideslope and/or localizer to yellow. The symbol generator also flashes the affected pointer at four hertz.
E. The ILS deviation warning continues as long as the airplane exceeds the glideslope/localizer limits and the arming conditions exist.
F. Testing (Fig. 1, Part B)
(1) The ILS Deviation monitor can only be tested when the airplane is on the ground. The EFIS test function is disabled by an air/ground relay when the airplane is in flight.
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A
757
MAINTENANCE MANUAL
AFDS PITCH AFDS PITCH MODE - ENGAGED GLIDESLOPE DEVIATION SCALE
GLIDESLOPE DEVIATION POINTER
AFDS STATUSAFDS ROLL MODE - ARMED AFDS ROLL MODE - ENGAGED
LOCALIZER DEVIATION POINTER
POINTER - MAGENTA
3
DEVIATION
SCALE - YELLOW
POINTER - MAGENTA
3
DEVIATION
SCALE - YELLOW
PART B - GROUND TEST
TEST MESSAGE "OK" OR "FAIL"
FAILURE MESSAGE-CP (CONTROL PANEL); DU (DISPLAY UNIT); AND SG (SYMBOL GENERATOR) POINTERS BLINKING AT FOUR HERTZ
ILS Deviation Monitor - EADI Display
Figure 1
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