Flight Instruments, Displays -EFIS System Description 737 Operations Manual
Glide Slope and Localizer Deviation Displays
Glide slope and localizer deviation scales appear when a localizer frequency is tuned on the associated VHF NAV receiver. A valid signal is required before the deviation pointer is displayed.
The normal localizer deviation scale is one degree per dot. When the course deviation is approximately 5/8 degree deviation (5/8 dot) and VOR/LOC is engaged, the scale automatically expands to indicate 1/2 degree deviation per dot. The scale remains expanded until after landing rollout or on a go-around with radio altitude greater than 200 feet.
On all airplanes except serial numbers 27635 and 28085: On a backcourse approach, the symbol generator reverses the polarity of the localizer deviation pointer on the EADI. The reversal occurs when the airplane track differs from selected MCP course by more than 90 degrees. Thus, when the frontcourse is set in the MCP course display, the EADI and EHSI course deviation display will agree on both a frontcourse and a backcourse approach. Additionally, the glideslope scale is not displayed for a backcourse approach.
ILS Deviation Warning
ILS deviation monitoring alerts the flight crew of excessive LOC or G/S deviations. This alerting function is operative during single or dual A/P channel ILS approach. The alerting system is armed when the airplane descends below 1,500 feet radio altitude (RA) with the LOC and G/S captured. If the Captain’s or the F/O’s LOC deviation exceeds one–half dot expanded scale (one–fourth dot standard scale), the respective LOC scale changes color from white to yellow, and the miniature runway stem flashes.
If the Captain’s or F/O’s G/S deviation exceeds one dot deviation, the respective G/S scale changes color from white to yellow, and the G/S pointer flashes. G/S deviation alerting will not be initiated below 100 feet RA, but continues to operate below this altitude if the alert was triggered prior to descent below 100 feet RA.
Each pilot’s alerting system self–tests upon becoming armed at 1,500 feet RA. This self–test generates a two–second LOC and G/S deviation alerting display on each EADI.
Rising Runway Symbol (as installed)
The rising runway symbol is an integral part of the LOC deviation display and is positioned at the top of the LOC deviation pointer. the rising runway symbol is displayed in addition to the digital radio altitude display and gives an additional cue to the flight crew of the aircraft’s close proximity to the ground as the airplane descends below 200 feet radio altitude. Full scale, vertical movement of the rising runway represents the last 200 feet of radio altitude. Zero feet radio altitude is indicated as the top of the runway symbol rises to the base of the airplane symbol.
Flight Instruments, Displays -EFIS System Description 737 Operations Manual
The requirements for display of the rising runway symbol are as follows:
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valid ILS/LOC frequency selected
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valid radio altitude data
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radio altitude less than 2,500 feet. If any of the above conditions are not met, the runway symbol is not displayed.
Pitch/Roll Comparator (as installed)
A yellow “PITCH” or “ROLL” alerting annunciation is displayed on both EADIs if either symbol generator detects a difference of more than 3 degrees between the Captain’s and F/O’s pitch or roll displays. A short time delay is incorporated to minimize nuisance annunciations.
Radio Height Alert (as installed)
The radio height alert is triggered when the airplane descends below 1,000, 1,500 or 2,500 feet AGL. The alert is turned off when the airplane continues to descend below 500 feet AGL or climbs above the trigger altitude, or after pressing the decision height reset switch on the EFIS control panel.
Digital Radio Altitude and Decision Height
When radio altitude is less than 2,500 feet, a digital display of radio altitude is depicted in the lower right hand corner of the EADI. At all other times, the digital radio altitude display is blanked.
When a positive decision height has been selected on the related EFIS control panel, the letters “DH” and the decision height are displayed just above the digital radio altitude display of the associated EADI.
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