c. EHSI Modes. The EHSI allows for multiple
display formats. See Table 3B -3 for the display
formats that are selectable from the control panel.
Table 3B-3. EHSI Display Modes
HSI (360° compass)
HSI ARC (Partial 80° compass)
Map ARC (Partial 80° compass)
Map (360° reference)
d. EHSI Outputs. The EHSI outputs the
following to the flight director:
(1) HDG Datum.
(2) CRS Datum.
(3) LOC Tune if the course source is LOC.
(4) Lateral Deviation.
(5) Glideslope Deviation is sent to the flight
director when it is available.
(6) Roll Steering. The bottom MFD outputs
roll steering to the flight director when the flight director
is valid and the course source is FMS.
e. HSI Graphic Format. The following graphics
are utilized on the EHSI during the HSI Mode.
(1) Course Readout/Label. When a valid
source is tuned, the course selected is displayed in
white. Next to the course readout is the label CRS or
DTK in white letters. The digital CRS or DTK readout
is always associated with the course source.
(a) Radial Source (VOR). The course
label is CRS and the digital course readout is
independently controlled by each MFD control panel.
(b) FMS -800 Operation. The label is
CRS when the primary source is not FMS. If the
primary source is tuned to FMS, the CRS will be
replaced with Desired Track (DTK) for all FMS modes
except TO / FROM mode (TACAN Emulation). When
FMS is the course source the course is automatically
set by FMS.
(c) KLN 90B Operation. Refer to OBS /
LEG switch in Paragraph 3D-20 for a description of the
(2) Message Alert. The message (MSG)
alert appears whenever the FMS sends an alert to the
MFD. The yellow MSG alert indicates to the crew that
they should look at FMS on the selected side of the
cockpit [on-side/x (cross) side].
(3) FMS -800 Heading Bug. The FMS
heading bug is only available for display when the
FMS-800 is the NAV source and the FMS is
commanding the bug to be displayed. The FMS
heading bug is white and travels about the aircraft
symbol around the outer edge of the compass. The
center of the FMS heading bug indicates the selected
heading in 1 increments. When the FMS selected
heading is set, the FMS NAV source label is replaced
with FHDG 1 in white letters. If the FMS selected
heading is invalid, unavailable, or the primary course
source is not FMS 1, the heading bug will not be
displayed. The FMS selected heading bug is
displayed in yellow when a cross-side source is
(4) Course Deviation Scale. Four white
lateral deviation scale dots indicate deviation from
course. The course deviation scale rotates about the
aircraft symbol such that the scale is always
perpendicular to the selected primary course. The
maximum deviation is 2.5 dots. When the selected
course or source is invalid, the course deviation scale
is removed from the display.
The EHSI outputs lateral deviation and lateral
deviation validity to the flight director and/or autopilot.
The lateral deviation validity signal corresponds with
the selected course sources lateral deviation. The
lateral deviation output flag is displayed when the
lateral deviation for the selected primary navigation
source is invalid or an MFD failure results in bad or
failed lateral deviation output.
(5) Vertical Deviation Scale. The Vertical
Deviation Scale, four small circles located on the right
side of the MFD indicate the vertical deviation of the
(6) Vertical Deviation Pointer. The Vertical
Deviation Pointer, represented by a white star,
displays the deviation with respect to the selected
(7) Lateral Deviation Bar. The center of the
course pointer moves laterally with respect to the
aircraft symbol and the four white deviation scale dots
to indicate lateral deviation. The course deviation
scale rotates about the aircraft symbol so that the
scale is always perpendicular to the selected primary