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The freewheeling assembly is mounted on the lower malfunction.
portion of the engine power and accessories gearbox.
Its freewheeling mode allows free rotation of the rotor
system as well as necessary accessories when power 2 - 4 9 . TRANSMISSION O I L COOLING
is not being applied by the engine. The freewheeling SYSTEM.
assembly is equipped with an electromagnetic chip The oil cooling system is located aft of the engine. It
detector. consists of a heat exchanger/blower unit that is shared
The chip detector has a fuzz burner capability that can with the engine oil cooling system. The fan of this unit
distinguish between a buildup of normal wear particles is attached to the tail rotor driveshaft and forces air
and larger metal particles due to possible component through the heat exchanger.
failure. The chip detector automatically attempts to
burn off fuzz accumulations electrically. A CHIPS ENG
FREEWHEEL caution message will be displayed on the 2 - 5 0 . I N D I C A T O R S AND C A U T I O N
MFD when contact is made across the chip gap of the MESSAGES.
chip detector. If the particles exceed the burnoff
capability of the chip detector, the caution message will a . Transmission O i l Pressure I n d i c a t i n g
remain. If burnoff is accomplished, the message will be System. An oil pressure transducer is located on the
deleted. deck aft of the transmission. This transducer transmits
a signal to the vertical scale TRANS OIL instrument
NOTE located on the MPD (fig. 2-6). Power is supplied
through the battery emergency bus.
After three successful burnoffs of a chip b. Transmission Oil Temperature Indicator. The
detector during any flight, the helicopter transmission oil temperature indicator is a vertical scale
shall be reported to maintenance, as soon instrument located on the MPD. I t measures
as practical, for a serviceability check of the transmission oil temperature in degrees Celsius. Power
freewheeling assembly. to the instrument is supplied through the battery
emergency bus. Signals are received from a
2-47. MAIN DRIVESHAFT. temperature sensor located on the oil filter assembly.
The main driveshaft transmits engine power from the c . Transmission Oil Pressure Low Caution
freewheeling assembly to the transmission. The Message. When the lower transmission oil pressure
driveshaft is equipped with nonlubricated flexible limit is reached, a LOW OIL PRESS XMSN caution
couplings at each end to accommodate minor (normal) message will be displayed on the MFD and an audio
misalignments between the main transmission and the tone will sound. Signals are received from the oil
engine mounted freewheeling unit. pressure transducer.
2-38
TM 1-1520-248-10
d. Transmission Oil Temperature High Caution 2-51. FILTER BYPASS INDICATOR.
Message. When t h e u p p e r t r a n s m i s s i o n o i l
temperature limit is exceeded, a HIGH OIL TEMP The transmission oil filter is equipped with a pop-out
XMSN caution message will be displayed on the MFD filter bypass indicator. When the main element
and an audio tone will sound. Signals are received from becomes clogged, the filter button on the end of the
the oil temperature sensor. filter housing will pop out indicating that oil is bypassing
the first element and is being filtered only by the
second element. This button cannot be reset unless the
e . Transmission Ten Second Overtorque filter housing is removed. The primary filter element
Limit. When 100% mast torque is exceeded, a HIGH must be replaced and the secondary element must be
TRQ TIME LIM (nn) caution message will be displayed cleaned prior to the next flight.
on the MFD and an audio tone will sound. In the
brackets on the right side of the caution message, the
time in seconds that the torque has remained in this 2-52. OIL LEVEL SIGHT GLASS.
caution range up to 99 seconds is recorded. When this
time exceeds 10 seconds or at any time the torque The oil level sight glass is located on the right side of
exceeds 116%, or if cumulative overtorques exceed 10 the transmission casing and is easily accessible for
seconds duration in one hour of operation, a XMSN visual reference. Normal oil quantity is indicated when
OVER TRQ warning message will be displayed on the oil level is within the yellow range of the sight glass.
MFD and an audio tone will sound. The warning Refer to Servicing Diagram (fig. 2-26).
message will remain on the MFD as long as the
warning condition exists, and it cannot be manually
removed. The warning message is automatically 2-53. TAIL ROTOR DRIVESHAFT SYSTEM.
entered into memory for future recall. Signals for these The tail rotor driveshaft system delivers torque from the
indications are received from mast torque sensing units freewheeling assembly to the tail rotor gearbox. The
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TECHNICAL MANUAL OPERATOR’S MANUAL FOR ARMY OH-58D HELICOPT(21)
