LX. The LX mode is the normal working
mode of the lightning sensor system. Lightning strikes
are collected, processed, and displayed.
CLR/TST. When clear/test is selected, all
memory of past strikes and symbols are erased. After 3
seconds the system enters the test mode.
In the test mode, simulated lightning signals are fed into
the test loop in the antenna and a lightning strike is
simulated at a bearing of 45 degrees at 25 nautical miles.
A lightning alert is also generated along the outermost
range ring at a bearing of 45 degrees. This simulated
strike will progress in severity through level three within
15 seconds of entry into the test mode. If the mode
selector is left in the CLR/TST mode, the alert and strike
symbols will reduce in severity and disappear. The
lightning rate symbol will disappear after approximately 2
The lightning sensor system antenna
is used in this test, and as a result,
any real lightning activity that occurs
while the test is in operation may
also be displayed.
Lightning Sensor System Display. The
LSS shows areas of lightning activity on the EHSI with
symbols. Each lightning symbol represents the center of
a circular area with a radius of nine nautical miles. Three
different lightning symbols are used to represent three
different rates of occurrence of the lightning within each
18 nautical-mile diameter circle. The lightning rate
during the last two minutes. The symbol's location on the
display represents the average position of the lightning
that has occurred during the last two minutes inside each
18 nautical-mile diameter area. Lightning may -not be
occurring at the center of the symbol. Because it is easier
for the LSS to detect lightning at close distances than at
far distances, the number of lightning strokes required for
each rate symbol is adjusted for distance to the storm.
Figure 3-32 shows the number of strokes required for
each symbol versus range to the storm. Figure 3-33
shows the three rate-of-occurrence symbols.
Lightning Alert System. It is possible to see
a lightning flash visually, and see no change in the
display. This is normal, because, unless one of the rate
thresholds are crossed, there will be no change in the
symbol, other than a slight position update. The lightning
alert function shows the operator that the unit is
operational, and shows real-time lightning activity. The
lightning alert function places a magenta rate-one symbol
near the outer range mark of the display, at the proper
bearing, for each lightning flash (fig. 3-33). The lightning
alert symbol is displayed for five seconds, and gives the
operator confidence that the system is functional even
though there may be no change in the white lightning rate
symbols. It is also an indicator of real-time activity.
Annunciations. The following mode annunciations may
appear on the EHSI display.
LX/F (amber). Indicates that self-test
has detected a fault.
LX/S (green). Indicates that the
system is in the standby (SBY) mode.
LX/CL (green). Indicates that the
system is in the clear (CLR) mode. This annunciator will
appear for approximately 3 seconds after the CLR/TEST
mode has been selected. After this time the mode
annunciator will switch to LX/T.
LX/T (green). Indicates that the
system is in the test (TST) mode. This annunciator may
be replaced with LXMN.
LXmn (amber). In the CLR/TST
mode an amber LXmn will be displayed, where mn is a
two digit failure code. Table 3-13 explains these codes.
Figure 3-32. Lightning Strokes Required per Symbol vs.
Range to Storm