737 Flight Crew Operations Manual
Flight Instruments, Displays -
Head-Up Display System
Description
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
10.22.2 D6-27370-866-EGP
Overhead Unit (OHU)
The OHU contains the CRT and projection optics to display flight symbology on
the combiner. Electronic circuitry within the OHU controls display intensity and
system monitoring.
Combiner
The combiner optically combines flight symbology from the OHU, with the
pilot’s view through window No.1. It acts as a wavelength selective mirror,
reflecting only the flight symbology color (green) and lets other colors pass
through.
The combiner alignment detector monitors the angular position of the combiner.
The HUD computer uses the detector to verify correct combiner position for
normal viewing. If the combiner is not in the correct position, and the HUD is in
the IMC or VMC modes, the ALIGN HUD message appears on the combiner.
The combiner glass element has a break away safety feature which allows the
element to rotate forward from the normal position, in case of abnormal
deceleration.
Control Panel
The HUD control panel is used to select and display modes of operation and enter
data. Display intensity is controlled by panel switches or by an ambient light
sensor located on the upper left corner of the panel.
Annunciator Panel
The annunciator panel consists of lights to indicate HUD system status
annunciations during AIII mode approach and landing operations.
Modes of Operation
The HUD system provides a mode–selectable display on the combiner. The modes
are:
• PRI (Primary) - used for most HUD operations
• AIII - primarily used for manually flown CAT II or CAT IIIa ILS
approach and landing operations
• IMC - used for AFDS autopilot/flight director approaches
• VMC - used for visual approaches.
September 26, 2013
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