heading annunciator. The heading is labeled HDG in
black letters on a solid red box.
Autonomous Integrity Monitoring Alert. The display
annunciates Dead Reckoning (DR) or Receiver
Autonomous Integrity Monitoring (RAIM) in yellow to
the right of the digital heading readout. If DR and
RAIM Alert are present at the same time, DR overrides
the RAIM Alert.
The FMS goes into DR when it loses navigation
sources. When FMS goes into DR, it calculates its
present position based on inertial data. The display
annunciates DR in yellow to the right of the digital
(25) Offset. The crew can select a parallel
offset (OFST) source via the FMS. The lateral
deviation scale is relative to the parallel offset course.
OFST is annunciated to the right of the digital heading
readout in white.
(26) Wind Pointer. The wind indicator consists
of a green symbol loc ated on the outside edge of the
compass and graphically layered to not obscure the
heading bug symbol, lubber line, or heading readout.
The wind indicator rotates about the aircraft symbol
such that the arrow is always pointing into the
compass at the wind direction. The arrow displays
zero to five green fins on its tail to represent wind
speed. Long fins represent 10 knots and short fins
represent 5 knots. If the wind velocity is 0 knots, the
arrow is removed from the display. If the wind velocity
is less than 2.5 knots the arrow is displayed with no
fins. The wind indicator indicates wind from .1 knots to
45.5 knots. If the wind exceeds 45.5 knots, the wind
indicator changes to a maximum wind symbol (wind
indicator with a filled triangle fin at the tail). When the
wind speed or wind direction is invalid or unavailable,
the wind indicator is removed from the display.
(27) To/From Indicator. A white triangle to or
from indicator rotates around the aircraft symbol on the
course needle. It indicates TO the station when the
triangle points towards the head of the course needle
and FROM the station when the triangle points
towards the tail of the course needle. If FMS is the
selected course and FMS outputs a waypoint alert, the
TO / FROM flag flashes.
If the course source is not FMS, the indicator is
set to TO when the angular difference between the
relative bearing to the station and the primary course
is less than 89. When the angle is greater than 91
FROM is indicated. The indicator is OFF when the
angle is between 89 and 91. When FMS is the
primary source then the FMS determines the TO /
FROM indication. If the TO / FROM indication is
invalid or unavailable, an active navaid has not been
selected, or the indicator is OFF, the TO / FROM flag
will be removed from the display.
(28) Aircraft Symbol. The white aircraft
symbol is located in the center of the compass rose.
f. EHSI Operations.
(1) OBS Backup Mode. When the heading is
invalid the compass rose rotates about the aircraft
such that the selected course is always referenced at
the top of the display. When the selected course is
invalid the compass freezes at the last known position.
navigation information for the selected course is
flagged invalid, the course source label is removed
from the display and replaced with the course source
annunciation drawn in black on a solid red box. The
deviation bars and scale are removed from the display
with a navigation flag. If the primary course goes
invalid, the selected course readout is replaced with
red dashes. If FMS-800 or the KLN 90 is selected and
an FMS NAV Warn occurs (RAIM Alert), the MS NAV
source annunciator turns yellow and all the navigation
information remains on the display.
(3) LOC/BC. If an LOC frequency has been
tuned and backcourse is selected on the flight director,
BC is displayed in place of the LOC source. Once BC
has been set it will remain set as long as the BC
discrete is set.
g. HSI ARC Format. The compass arc format,
Figure 3B-9, is a graphical representation of the
current heading of the aircraft. It is similar to the
compass rose except only an 80 slice is shown. The
arc format is an expanded compass with the compass
segment at the top of the display and the aircraft
symbol centered laterally at the bottom. The compass
rotates about the center point of the aircraft such that
the current heading is indicated directly below the
The HSI format with the 360 compass rose
display is the same as the HSI Arc display with the
(1) Selected HDG Readout. A digital readout
of selected heading is displayed in the upper left-hand
corner of the display. When the heading bug is visible,
it will appear when the selected heading is changed
and is removed 10 seconds after the heading bug
quits moving. If the heading bug is off the screen, the
readout is constantly displayed.