TM 1-1510-225-10 3C-61 (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. (b) Excessive Terrain Closure Rate (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 UPindicator 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
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