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MAINTENANCE
Honeywell U&!#h.
Each display unit transmits data to the fault warning computer (FWC) over
a
private-line
(ARINC 429)
bus,
referred
to as the DU wraparound
bus.
~~;m~;ntent of the data varies depending on DU position and display
. All six DUS transmit activity counter information. The FWC
monitors for activity on the DU wraparound bus by way of the activity
counter. The CHECK DU message is activated whenever the FWC fails to see
any activity on the wraparound bus for DUS 1, 2, 5, and 6.
The message
is displayed as appropriate for the DU'S positional location (1, 2, 5,
and 6) in the aircraft.
The ENG annunciation is activated on the PFD whenever the FWC fails to
see any activity on the wraparound bus for DU3 (or DU4 with compacted
EICAS format). The DU4 annunciation is activated on the PFD whenever the
FWC fails to see any activity on the wraparound bus for DU4 when not
displaying compacted EICAS format.
The DUS displaying the PFD format additionally transmit attitude (pitch
and roll), speed (CAS or Mach), and altitude information. The FWC
compares the attitude data received from the PFD's wraparound bus with
the pitch and roll ARINC 429 data received from the IRS'S.
It also
compares the speed and altitude data received from PFD's wraparound bus
with the CAS or Mach and altitude ASCB data from the DADC'S.
If the
difference between the display and sensor data exceed the appropriate
threshold for any one parameter, the CHECK DU(X) message is activated;
where (X) is position of DU in the aircraft which is displaying
miscompared PFD data.
If the miscompare occurs on both PFDs, then the
red CHECK PFD message is displayed. The DUS displaying engine data
format additionally transmit left and right EPR, left and right TGT, and
left and right N1 and N2 information. The FWC compares the engine data
received from DU3 (or DU4 with compacted EICAS format) with the ASCB data
from the data acquisition units (DAUS). If the difference between the
display and sensor data exceed the appropriate threshold, for any one
parameter, the ENG annunciation is activated on the PFD.
Provisions for external light sensors are included as inputs to the DUS,
however, short-term light changes are adequately corrected for by the
DU'S own light sensor located on the front of the DU, while long-term
changes in light conditions is accounted for by the DP-884 Dimmer Panel.
The display unit compares the adjacent light sensor (ALS) input (the
display light sensor (DLS) output from the adjacent tubes) with its own
light sensor and uses the larger value to program brightness so that the
tubes track each other. Weather radar returns displayed on the two
navigational displays (NDs) can be dimmed independently by using the
brightness knob on the weather radar controllers. A 10-minute warmup
period is required after power is initially applied to the DUS before
color stabilization is complete. Degaussing procedures are provided in
the Gulfstream aircraft maintenance manual.
22-14-00
Page 149
Aug 15/91
Use or disclosure
of information
on this pege is subject to the restrictions
on the title page of this document.
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