NAVIGATION AND
COMMUNICATION
AIRPLANE
OPERATIONS
MANUAL
2-18-75
Page
4
Code
01
REVISION 39
HGS COMPONENTS
HGS COMPUTER
The HGS Computer receives input signals from other airplane sensors
and generates a symbology set that is transmitted to the Overhead
Unit. The displayed symbology depends on the selected mode of
operation. During AIII mode approaches, the HGS Computer monitors
the approach performance and displays appropriate messages to the
pilot and on the Primary Flight Displays (PFD).
The HGS Computer is located in the forward avionics bay and is
powered by the DC Bus 1.
HGS CONTROL PANEL (HCP)
The HCP is used for setting glideslope angle, runway length and
elevation, and for selecting HGS active and standby modes of
operation. It also provides an indication of the system’s ability to
provide Cat IIIa guidance.
Powered by the DC Bus 1, the HCP is located in the center pedestal
and is available to both pilots.
Display luminescence is controlled automatically and based on
existing ambient light. An ambient light sensor mounted on the front
panel of the HCP measures the ambient light conditions and provides
the necessary input to the internal circuits that control the display
luminescence.
OVERHEAD UNIT (OHU)
The OHU generates flight symbology on a cathode ray tube (CRT) and
optically projects the symbology onto the Combiner. The OHU is
located above the pilot's head in a position that provides the proper
spatial relationship in relation to the Combiner and the airframe. This
relationship permits various symbols, such as the artificial horizon, to
overlay the corresponding features of the outside scene.
The OHU is powered by the DC Bus 1.
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