TM 1-1520-238-T-6
9–105
9–7.
SYSTEM DESCRIPTION (cont)
9–7
(16) Audio Warning System.
The audio warning system (fig. 9–95) provides auditory signals to alert the
pilot and CPG of hazardous engine, main rotor speed or stabilator conditions.
(a) ENG WARN circuit breaker (CB52), located on the pilot center circuit breaker panel, supplies
28 VDC emergency dc bus power to the engine out warning unit.
(b) The engine out warning unit monitors both engine power turbine speeds (NP), engine gas turbine
speeds (NG), the power lever position of both engines, and torque developed by each engine. NP sensing is
disabled when the respective engine torque is above 100 foot-pounds. Np sensing is also disabled when the
respective PWR lever is not in the FLY position. With the PWR lever in the FLY position, if Np decreases to 92%
and torque is below 100 20 foot-pounds, the respective engine out sensor develops a signal to turn on the
respective ENGINE OUT indicator on the pilot and CPG master/caution warning panels and triggers the engine
out warning unit. The engine out warning unit generates a 700-1700 Hz sweep tone to the pilot and CPG
headsets. If the PWR levers are moved from the FLY position, Np sensing is disabled. However, when NG
decreases to 63%, the engine out warning is triggered. The engine out warning tone can be reset by pressing
either the ENGINE 1 OUT or ENGINE 2 OUT indicator on the master caution/warning panel.
(c) If the speed of the main rotor (NR) decreases to 92% (266 rpm), the engine out warning unit
develops a signal to turn on the LOW RPM ROTOR indicator on the pilot and CPG master/caution warning panel
and triggers a 700-1700 Hz sweep tone to the pilot and CPG headsets. If the rotor rpm increases to 104% (301
rpm), the HIGH ROTOR indicator turns on, but an audio tone is not generated. The low rotor speed warning tone
can be reset by pressing either the ENGINE 1 OUT or ENGINE 2 OUT indicator on the master caution/warning
panel.
(d) If the stabilator automatic control system fails, the stabilator triggers the engine out warning unit. The
engine out warning unit outputs a 1000 Hz continuous tone to the pilot and CPG headsets. The stabilator tone is
reset by the stabilator RESET button on the respective collective stick.
