MD Helicopters 369-500, Maintenance Instructions Manual

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CSP-HMI-3
MD Helicopters, Inc
.
MAINTENANCE MANUAL
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[ Chapter 95 TOC ]
95-30-00
Page 3
Revision 7
The information disclosed herein is proprietary to MD Helicopters, Inc.
Neither this document nor any part hereof may be reproduced or transferred to
other documents or used or disclosed to others for manufacturing or any other
purpose except as specifically authorized in writing by MD Helicopters, Inc.
Copyright
©
1999 − 2016 by MD Helicopters, Inc.
from the torquemeter pressure port of the
engine through metal and nylon tubing to the
gauge.
14. Engine Out Warning System (369D/E/FF −
500N)
An internal malfunction requires replacement
of the EPO warning control unit. (Unit does
not have accessible internal adjustments.)
The engine out warning system consists of an
Autronics Engine Power Out (EPO) Warning
Control Unit (EPO warning control unit), an
audible warning horn and interconnecting
electrical wiring. The system functions with
the engine out warning light of the caution
and warning lights system (Ref. Caution and
Warning Indicator Lights, Sec. 95-30).
(Slim-Line instrument panels only) The
sensing equipment senses both N
1
and main
rotor (N
R
) low speeds, and activates engine
automatic reignition system installed as
standard equipment on Model 369D helicop­
ters S/N 1150 and subsequent. Automatic
reignition system is optional equipment on
Model 369D helicopters S/N 3-1149.
The system provides a visual and an audible
indication of low speed(s) as follows:
A. N
1
/N
R
Sensing Equipment
The N
1
/N
R
sensing equipment uses an EPO
warning control unit described below, N
R
disable switch S199 located on the base of the
inboard collective pitch stick, and resistor and
diode board TB106.
The EPO warning control unit monitors engine
N
1
speed. Engine low RPM, N
1
, is sensed by
EPO warning control unit monitoring the
frequency of output ac voltage from N
1
tachometer generator.
When engine speed decreases to approximately
55% N
1
RPM or less, the EPO warning control
unit produces an output to flash the engine out
warning light and activates the EPO audible
warning horn which produces an audible
”beeping” in the crew compartment.
The EPO warning control unit provides
separate audio tone warning signals for
headsets. The tone warning signals occur and
the audible warning horn ”beeps” only when
the generator (GEN) switch is ON and N
1
speed is 55% RPM or less.
The engine-out warning light flashes regard­
less of GEN switch position.
N
1
/N
R
sensing equipment senses main rotor
(N
R
) low speed.
Low N
R
RPM is sensed by the EPO warning
control unit monitoring the frequency of the
output ac voltage from the main rotor (N
R
)
tachometer generator. N
R
sensing occurs at
main rotor speed of approximately 98% N
R
RPM, or less. When low main rotor (N
R
) speed
is sensed, the EPO warning light flashes and
the audible engine out warning signals are
activated. When the throttle is at idle or cutoff
position, N
R
disable switch activates to disable
N
R
sensing to prevent flashing the engine out
light and activation of both warning horn and
audible tone during engine idle and cutoff.
Designed-in time delay keeps N
R
sensing
disabled after N
R
disable switch is deactivated
for sufficient time to permit N
R
to be attained.
N
1
sensing circuits remain operational (are not
disabled) while N
R
sensing is disabled. The
EPO warning control unit produces the output
for flashing the engine out warning light,
”beeping” the warning horn and generates the
audible warning tone if low N
1
RPM occurs
while N
R
sensing is disabled.
B. Engine Out Warning System Functioning
The EPO warning control unit senses low
frequency ac output voltages from N
1
and N
R
tachometer generators to activate and control
warning light and audible indications.
When GEN-OFF switch is ON, a ground is
supplied to a tone interrupt circuit in the EPO
warning control unit to enable audio warning
tone circuits and to the audible warning horn
for ”beeping” when low N
1
RPM is sensed.
When low N
1
RPM is sensed, N
1
speed-sens­
ing circuits and flasher and tone control
circuits activate engine out flashing light and
audio tone No. 1, 2 and 3 generation circuits.
N
R
sensing circuits, with flasher and tone
control circuits, activate and control flashing
light and audio tone generation circuits for
operation at low N
R
RPM.
Audio warning tone No. 1 is routed through
the ICS system to headsets. The higher