TM 55-1520-228-10
WARNING
Illumination of the engine oil bypass light may
indicate a severe leak is present or developing,
which could result in total loss of engine oil in a
short period of time.
k. Engine Oil Bypass Caution Light. The ENG
OIL BYPASS caution light (figure 2-13 and figure 2-14),
located on the caution panel, will illuminate when the oil
tank level is approximately 3 pints low. With the ENG
OIL BYPASS switch (figure 2-12) in the AUTO position
the engine oil will bypass the oil cooler. A significant
rise
in engine oil temperature will occur and engine failure
can occur in a few minutes due to excessive engine oil
temperature and/or engine oil loss. The switch in AUT
O
position is designed for combat operations only (due to
the potential for damage to the oil cooler by hostile fire)
to provide the pilot a little additional time to fly out of the
immediate enemy danger area only. The switch should
be in the OFF position for operation in noncombat envi-
ronment. The circuit is powered by 28 Vdc and is pro-
tected by the CAUTION PNL LTS circuit breaker.
l. Engine Chip Detector. There are two electri-
cal engine chip detectors located in the accessory gear
case, one at the lowest part and one on the forward right
side by the oil pump. The ENG CHIP DET caution light
(figure 2-14), located on the caution panel will illuminate
when sufficient metal chips to complete the electrical cir-
cuit are collected from the engine oil. The system is
poweredby28VdcandprotectedbyCAUTIONPNL
LTS circuit breaker.
SECTION IV. FUEL SYSTEM
2-22. FUEL SUPPLY SYSTEM.
Manual fuel shutoff valve should only be used
in emergencies and maintenance procedures
that require its use. Alert maintena
nce person-
nel anytime engine is shut down by using man-
ual fuel shutoff valve by making an entry on DA
Form 2408-13-1.
The OH-58A/C helicopters are equipped with a
self-sealing Crashworthy Fuel System. This sys-
tem is designed to retain fuel
in a crash and provide
improved ballistic protection, and is located below and
aft of the passenger seat. In addition, the fuel lines are
self-sealing. Mounted in t
he bottom of the cell is one
boost pump, one fuel quantity transmitter, one low fuel
transmitter, and one fuel sump drain. Installed in top of
the cell is one fuel quan
tity transmitter, a vent line, and a
boost pump pressure switch. A fuel filler cap is located
on the right side just aft of the passenger door. The fuel
shut off valve is moun
ted on the right side of the aircraft
above the fuel cell cavity and is manually operated by
the fuel valve handle on the overhead console. A con-
nector for an auxi
liary fuel cell is located on the forward
side of the fuel cell beneath the seat. Helicopters with
crashworthy fuel systems also incorporate the closed
circuit refueli
ng provision.
2-22.1. AIRFRAME MOUNTED FUEL FILTER AS-
SEMBLY. After compliance with MWO 1-1520-228-
50-48.
The OH-58A/C helicopters have been equipped with an
airframe mounted fuel filter. The fuel fil
ter is a cylindrical
unit mounted on the engine deck on the left side of the
engine compartment. The fuel filter has a 10 micron
(nominal) disposable filter element an
d electrical means
of indicating any impending bypass condition which may
occur. Fuel enters the inlet port of the filter from the
fuel supply system and routes the f
uel through the filter
element, then exiting the outlet port of the filter to the
engine fuel pump. If a clogging condition should develop
in the filter element, a normall
y-openswitchisclosed
by differential pressure, lighting FUEL FILTER caution
panel as warning that further clogging may cause fuel to
flow through the bypass val
veinthefilterandontothe
engine pump with filtration.
2-23. AUXILIARY FUEL SYSTEM.
An auxiliary fuel cell (figure 2-15) can be installed in the
helicopter. The auxiliar
y fuel cell, when installed, is se-
cured in the passenger compartment on the right half of
the cargo platform. The auxiliary fuel cell is a self-sup-
porting, crashworth
y self-sealing bladder type.
a. This fuel is delivered to the main fuel system
by gravity only; the p
ilot has no control over the flow of
fuel from the auxiliary cell into the main fuel cell.
b. The auxiliary fue
l cell can be filled either at the
main fuel cell filler or at a filler cap on the auxiliary fuel
cell. The preferred method is to service the helicopter
with fuel at the mai
n fuel filler.
c. When the auxiliary fuel cell is installed, a fuel
calibration card m
ustbeusedtodeterminetheamount
of fuel on board (figure 2-15).
2-28 Change 12
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