JT15D Engines Spring 2004
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JT15D Oil Leak
— Ken Kuchenreuther
Over the years we have written many Duncan
Intelligence articles about oil leaks (archives can
be accessed at www.DuncanAviation.com).
Searching the JT15D archives could be especially
valuable if you are new to an aircraft with JT15D
engines. However, the reason for this article is to
target one area of the JT15D that has initiated
some concern – oil leakage in the exaust duct
area. The JT15D has an emergency fuel shutoff
mechanism in the #4 bearing housing.
Incorporated in this assembly is a plunger
situated behind the aft face of the low turbine
shaft. When pushed — an uncoupled low turbine
shaft the plunger will shut off fuel thus
preventing an overspeed of the low pressure
turbine assembly and possible catastrophic,
uncontained release of the disks and blades.
The good news is I’ve never heard of this
catastrophe. However, what has been found is the
plunger tends to rub on the low turbine shaft for
various reasons. One reason being the low turbine
isn’t properly seated. JT15D history has shown
that this is most often the result of removing the
exhaust duct for maintenance and the plunger is
replaced per the maintenance manual due to
wear. The shaft itself exhibits no damage. The oil
leak becomes evident when the plunger, with its
seal effectiveness compromised due to the excess
heat, begins to leak.
Recently, we identified a JT15D-5D with an oil
leak in the exhaust duct. After disassembly, the
plunger was found with some metal buildup and
the shaft face worn. Replacement of the shaft was
required. On Oct 31, 2003, the maintenance
manual was revised to change the low turbine
seating procedure from torquing the low turbine
bolt to seating the low turbine using about 9000
pounds of force and heat. This good idea, initiated
— Pratt & Whitney, seems better suited for
assembling two dry, splined, interference fit
metal shafts. If you are performing this
maintenance, or are having it done —
someone, be aware of the difference between
pounds force and pounds per square inch.
Pratt & Whitney SIL # JT15D-038 has
information dealing with this subject. For
more information please contact Ken
Kuchenreuther at 800.525.2376.
Lightning Strikes
— Dan Arrick
Spring and Summer are the seasons for
lightning strikes on airplanes. If you suspect
your aircraft has been subjected to a lightning
strike, a visual inspection of the engine inlet is
required. If evidence of arcing (pitting, black
scarring) is present on the inlet cone or LP
Compressor (Fan) blades, remove the engine from
service. Return the engine to an approved
overhaul facility for lightning strike Special
Conditions inspection in the appropriate
Overhaul Manual.
Trivia Question
— Dan Arrick
The previous question was: On JT15D-1 through -4 series engines,
what is the purpose of the Step Modulator?
The Step Modulator ensures effective fuel
control at all operating altitudes. To check for
proper operation, look for ITT and Fuel Flow
increases when the engine anti-ice or ignition is
turned on.
This edition’s question is:
What is the purpose of the cold or hot
nozzle installed on a JT15D?
The first 10 callers with the correct answer
will receive a small prize. Please respond to
Dan Arrick — calling 800.525.2376.
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