When target alert is selected on the weather radar
controller, TGT in green is displayed on the EHSI. If a
level 3 weather radar return is detected within 7.5
degrees of aircraft heading, but beyond the selected
radar range, the annunciator will change TGT to amber.
(2) Range ring and annunciator. The range
ring and annunciator is displayed only when WX, NAV,
and NAV/WX format is selected. The range is selected
on the weather radar controller. One-half the selected
range is annunciated in white beside the half range ring.
If weather radar range control is not available, the range
default value will be 50 nautical miles.
(3) Weather radar modes. Weather radar
mode is annunciated on the EHSI.
(4) Weather radar return display. Weather
radar (WX) mode, weather radar information is displayed
(5) Lightning sensor system display. Three
levels of lightning activity are displayed using a white
lightning symbol. A magenta lightning symbol is used to,
annunciate activity at an unknown range.
Annunciations (fig. 3-18).
(1) Same compass source or navigation
source. When both the pilot and copilot select the same
compass or navigation source, the source annunciators
will be amber.
(2) Cross-switched navigation sources. If
the pilot selects the copilot's navigation source (VOR2)
or if the copilot selects the pilot's navigation source
(VOR1), the annunciator will be amber to indicate cross-
switched navigation sources. If both the pilot and copilot
select TACAN as the navigation source, TCN will be
annunciated in amber.
(3) DME hold. When DME is set in the hold
position, an amber H is displayed to the left of the
numerical DME readout.
(4) Waypoint annunciations. An amber
WPT annunciation from the long range navigation
system (INS) is displayed to indicate waypoint passage.
(5) Cautions due to failures of DME, GSPD,
or TTG. When distance measuring equipment (DME),
groundspeed (GSPD), or time-to-go (TTG) systems fall,
the digital displays will be replaced by amber dashes. If
NAV1 distance information is not available due to
TACAN selection, an amber N/A will appear in the
If one pilot selects TCN but the other pilot
selects NAV1 navigation source, the pilot
with the NAV1 data will have an N/A in the
distance display. If TCN is deselected,
distance data will return to the NAV1
(6) Target alerts. Weather radar target
alerts are annunciated on the EHSI. A green TGT
annunciation indicates an armed condition, while an
amber TGT indicates an alert condition.
Failure of course or heading select signals will cause
these displays to be replaced by amber dashes. They
are also dashed when the heading display is invalid.
(8) Weather radar failure. Failure of the
weather radar system is indicated on the EHSI by WX
EHSI Red failure annunciations (fig. 3-19).
(1) Heading failure. A failure of the heading
system results in the removal of bearing annunciators,
bearing pointers, course deviation pointer, and course
scale. The digital course readout and digital heading
readout will be dashed, and a red HDG FAIL will be
(2) Course deviation or glideslope deviation
failure. Failure of course or glideslope deviation systems
will result in the removal of course and glideslope
pointers and a red X will be drawn through the scale.
The letter G will appear at the zero deviation position of
the glideslope scale to identify the invalid information.
Table 3-3. Weather Radar Return Levels