(a) Excessive Sink Rate (Mode 1). Mode
1 provides visual and aural warnings for excessive rate
of descent with respect to terrain when below 2450
feet AGL. When the aircraft penetrates the outer
warning boundary, the "Sink rate" aural warning will be
given and repeated every 0.75 seconds, and PULL UP
indicator lights on the glareshield will begin to flash. If
the rate of descent is not corrected and the second
boundary is penetrated, the "Whoop, whoop, pull up"
aural warning will sound. The excessive sink rate
mode is independent of gear and flap configuration.
Refer to Figure 3C-32.
(Mode 2). Mode 2 provides visual and aural warnings
for excessive terrain closure rate. Refer to Figure
3C-33. The terrain closure rate mode is a function of
inputs of airspeed, radio altitude and rate of change,
barometric altitude, and gear and flap position. When
the aircraft penetrates the outer warning area, the
"Terrain" aural warning will sound twice and the PULL
UP indicator lights will begin flashing. If the excessive
closure rate condition remains uncorrected and the
inner warning boundary is penetrated, the "Whoop,
whoop pull up" aural warning will sound every
0.75 seconds. Upon climbing out of the inner warning
boundary, the "Terrain" aural warning will sound every
0.75 seconds, until the aircraft gains an additional
300 feet of barometric altitude.
Figure 3C-32. Mode 1 Excessive Sink Rate
Figure 3C-33. Mode 2 Excessive Terrain Closure Rate