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MANUAL. When either switch is at MANUAL, the respective
normal beep trim system is disabled (115-volt AC
from AC bus to the engine power turbine control box is
interrupted). When the switch is at AUTO (cover down),
the normal beep trim system is functional (115-volt AC
from the AC bus is reconnected to the associated engine
power turbine control box). Refer to Chapter 9 for emergency
engine trim operation.
CAUTION
Engine response is much faster when
RRPM is controlled with emergency engine
beep trim system. It is possible to
beep the rotor speed below safe operating
speed and low enough to disconnect the
generators from the buses. The generators
are disconnected at 85% to 82%
RRPM after a 3 to 7 second time delay.
b. Emergency Engine Trim Switches. Each momentary
switch is used to change the power turbine
speed of its respective engine if the power turbine control
box (normal beep trim system) malfunction.
When the normal trim system fails, the droop eliminator
also fails to function. Both switches have an INC, DECR,
and spring-loaded center position. When one of the
switches is held at INC, power from the essential DC bus
goes directly to the respective power turbine actuator
and increases the lever setting and the power turbine
speed. When the switch is held at DECR, the lever setting
is decreased, and the power turbine speed is decreased.
The emergency engine trim switches are to be used
when the normal beep trim system is disabled. If one of
the switches is used while the respective power turbine
control box is functioning normally, the power turbine
actuator setting will temporarily change but will return to
its original setting when the switch is released. Power to
operate the emergency engine beep trim switches and
actuators is supplied by the essential DC bus through the
NO. 1 and NO. 2 EMERG ENG TRIM circuit breakers on
the No. 1 and No. 2 PDP.
TM 1-1520-240-10
2-3-4
Figure 2-3-2. Emergency Engine Trim Panel 712
2-3-11. Emergency Power System. 712
CAUTION
To prevent damage, monitor the torque
and the PTIT indicators when operating
with emergency power. Failure to observe
these indicators could result in serious
damage to the drive train and engine.
An emergency power system is included with T55-L-712
engines. With the emergency power system, increased
power is available on pilot demand and is actuated by
raising the thrust control into the emergency power
range. Refer to Chapter 5 for limitations on its use.
When fuel flow increases to the point where PTIT is 890
to 910C, the EMERG PWR lights will illuminate on the
copilot and pilot instrument console (17, fig. 2-1-7 and 18,
fig. 2-1-9). If temperature is maintained in this range for
more than 5 seconds, the associated indicator will apply
28-volt DC from the ENGINE NO. 1 and / or NO. 2 START
& TEMP circuit breaker to the EMERGENCY POWER
panel. With 28-volt DC applied to the panel, the applicable
emergency power timer will start, and the indicator
will display a black-and-white flag. When thrust is reduced
below the emergency power level, the emergency
power light will extinguish and the timer will stop. However,
the emergency power indicator will continue to display
the black-and white flag. The flag can be reset on the
ground only.
WARNING
Before flight, be sure the two topping
stops are in their stowed position on the
right side of the console. If stops are not
stowed, be sure the stops are not installed
on the fuel controls before you start the
engine. Failure to check may result in inability
to achieve emergency power in an
emergency.
Topping stops are stowed on each helicopter. The stops
are installed on the N1 control of each engine for maintenance
engine topping checks. The stops provide an established
fuel flow when topping. When not in use, the
stops are stowed on the right side of the center console
aft of the pedals.
2-3-12. EMERGENCY POWER Panel. 712
The EMERGENCY POWER panel is located on the overhead
switch panel (fig. 2-3-3). It consists of an emergency
power indicator and a digital timer for each engine.
They are labeled NO. 1 and NO. 2 ENGINE. The timer
counts the minutes that emergency power is in use.
2-3-13. Oil Supply System.
The oil supply system is an integral part of the engine.
The oil tank is part of the air inlet housing and the filler
neck is on the top of the housing. An oil level indicator is
on the left side of the engine inlet housing. Refer to table
2-15-1 for the tank capacity. If the oil level decreases to
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