gearbox. Oil from the No. 3 and 4 bearings drains into the power turbine shaft
housing where, in normal ight attitude, it drains and passes through holes
in the rear case of the reduction gearbox. The oil is also partially scavenged
by the front element of the external scavenge pump and ejected into the
accessory gearbox sump.
When the engine is in a nose-up attitude, the oil collects at the rear section of
the power turbine shaft housing and is totally scavenged by the front element
of the scavenge pump, via the No. 3 bearing scavenge oil tube and one of the
external scavenge oil tubes. When the engine is in a nose-down attitude, all
the oil drains forward into the reduction gearbox sump. Oil is supplied to the
propeller governor, front thrust bearing, reduction gearbox accessory-drives
and torquemeter bleed-orice and drains into the gearbox sump. From the
sump, oil is scavenged by the rear element of the external scavenge pump
via a strainer in the front case of the reduction gearbox and a second external
oil transfer tube. The rear element of the scavenge pump forces the oil to an
airframe-mounted cooler from where it is returned to the oil tank via an inlet
adapter located at the 12 o’clock position on the compressor inlet case. Oil
ows from the adapter into a de-aerator tray installed at the top of the tank,
and drains into the tank.
Oil from the centrifugal breather, accessory gear shafts and bearings, input
gear shaft and bearing drains into the accessory gearbox sump where it is
scavenged by the rear element of the internal scavenge pump which forces
the oil into an externally mounted cooler. All oil supplied to the cooler is
returned to the oil tank.
Breather System
Breather air from the engine bearing compartments and the accessory and
reduction gearboxes is vented overboard through the centrifugal breather
installed in the accessory gearbox. The bearing compartments are connected
to the accessory gearbox by cored passages and existing scavenge oil return
lines.
The No. 1 bearing compartment vents rearward through the rear bearing
housing and oil tank center tube and into the accessory gearbox. The No. 2
bearing compartment is vented via the scavenge oil transfer tube. A bypass
valve, immediately upstream of the front element of the internal scavenge
pump, allows oil and air to be vented into the accessory gearbox under certain
transient operating conditions to prevent over pressurizing the No. 2 bearing
area. Under normal operating conditions, the valve is closed to prevent oil
ooding back into the tube assembly. The No. 3 and 4 bearing compartment
and the reduction gearbox areas vent to the accessory gearbox and oil tank,
respectively, through their scavenge oil lines. The oil tank is vented to the
accessory gearbox through the anti-ooding arrangement installed at the 11
o’clock position in the oil tank.
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