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pointers for glideslope and localizer signals, providing guidance for an ILS
approach. ILS information is supplied by VHF NAV #1 over an ARINC 429
data bus. A knob on the lower left corner of the attitude indicator is used to
select signal input to the glideslope and localizer pointers. The knob has
three (3) positions: OFF, ILS and B/C (for a back course approach). Both
the glideslope and localizer pointers have a warning flag to indicate power
off or lack of signal reception.
B. Digital Bearing and Distance Indicator (DBDI):
The dual DBDI (pilot and copilot) indicators provide a standby display of
heading, bearing, and distance to a selected navigation source
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-34-00
Page 13
October 11/01
Revision 5
independent of the Primary Flight Display (PFD). The indicators have dual
power supplies, each powered by the Essential or Emergency DC bus, with
only basic heading information available when operating on Emergency
DC bus power. The DBDI is illustrated in Figure 4.
During normal operation with all electrical sources available, the DBDIs are
powered through the Essential DC bus and display the following
information:
• Airplane heading beneath the lubber line at the top of the compass
card, sourced from the IRS system in use (pilot on #1, copilot on
#2).
• Pointer #1 (single shaft arrow) pointing to the currently tuned
navigational radio transmitter (VOR / VORTAC or ADF) selected
with the pointer switch on the lower left of the instrument. The
pointer will be positioned to the three o’clock position and a flag
displayed if no navigation radio is tuned or the signal is out of range
for the transmitter type selected.
• Pointer #2 (double shaft arrow) pointing to the currently tuned
navigational radio transmitter (VOR / VORTAC or ADF) selected
with the pointer switch on the lower right of the instrument. The
pointer will be positioned to the three o’clock and a flag displayed if
no nave radio is tuned or the signal is out of range for the transmitter
type selected.
• Digital DME distance readout is displayed in the window in the top of
the instrument for both (1 and 2) currently tuned VORTACs (only
dashes are displayed if no VORTAC is currently tuned). Distance is
indicated in one-tenth mile (0.1) increments up to 99.9 nautical miles
and one mile increments from 100 to 999 nautical miles.
• Digital display of the frequency of the currently tuned VORTAC if the
NAV selector is placed in HOLD mode, with the frequency preceded
by an H to indicate that HOLD has been selected. In normal NAV
mode, only dashes are displayed in the frequency space.
A failure of the heading information source (IRS #1 and IRS #2) prompts
the DBDI to automatically switch to an alternate heading source if one is
installed (typically AHRS or IRS #3). The use of an alternate heading
source is annunciated on the face of the instrument by the illumination of a
green AHDG light in the upper right corner of the instrument.
A more severe failure that involves the loss of primary and alternate
heading reference sources would automatically switch the DBDI to standby
mode, annunciated by the illumination of the amber STBY light in the upper
right of the indicator. In standby mode, the heading reference source is the
dual flux detector installation in the airplane wing tips. The flux detectors
act as magnetic compasses, sensing the horizontal component of the
magnetic field surrounding the earth. The magnetic direction sensed by the
flux detectors is corrected for errors (induced by the metallic structure of
the airplane) by a magnetic compensator before it is sourced to the DBDI
for use as the heading reference in standby mode.
Should there be a failure of the standby / flux detector system, a red STBY
light illuminates in the upper right corner of the instrument. The red STBY
will illuminate with a standby system failure even if the DBDI is operating in
the normal (IRS) mode.
OPERATING MANUAL
2A-34-00 PRODUCTION AIRCRAFT SYSTEMS
Page 14
October 11/01
Revision 5
The DBDI indicators annunciate system degradation and/or subcomponent
failure with the following displays:
• OFF flag in the upper left of the instrument indicates loss of
instrument power
• HDG flag at the lubber line at the top of the instrument indicates an
invalid compass signal
• Single shaft arrow flag on the left of the instrument indicates invalid
signal to the #1 pointer
• Double shaft arrow flag on the right of the instrument indicates
invalid signal to the #2 pointer
　
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