JT15D Engines Winter 2004
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ITT Fluctuations
— Dan Arrick
Duncan has recently received some calls
relating to fluctuations of ITT in flight. Though a
landing should be made as soon as practical for
repair, sometimes some troubleshooting can be
done in flight. When the circuit breaker is reset
and the fluctuation disappears for a period of
time, it may appear that the problem is the
indicator, but don't order a gauge over your cell
phone yet.
First, the ITT gauges are extremely reliable.
Second, 95% of problems of this nature are due
from wire breakage where the airframe wiring
meets the engine inlet temperature probe. If this
is the case, it is easily repaired with new alumel
or chromel terminals. The part numbers are
1-322337-0 and 1-322338-0, respectively.
Having overall engine balance checked and
possibly balancing the fan may help alleviate
future terminal breakage.
Engine Preservation
— Dan Arrick
Just a reminder to follow your Pratt & Whitney
JT15D Maintenance Manual requirements for
engine preservation. If your aircraft is down for
an extended maintenance visit or simply not
operating due to a pending sale, be sure to
preserve the engine oil and fuel systems to avoid
very costly problems. Even if the engines are in a
hangar or a low humidity environment, the
procedures should be completed.
Please feel free to call Dan Arrick or Ken
Kuchenreuther at 800.525.2376 for more
information.
ITT Splits
— Dan Arrick
An ITT split on JT15D powered aircraft is one
of the more common discrepancies we encounter
at Duncan Aviation. Other than being annoying to
pilots, an ITT split can be an indication of
deterioration in an engine. The first thing to
do is make sure the engine indication
systems are accurate. These include the N1,
N2 and ITT systems. Following accuracy
checks, try to determine which engine had the
shift causing the split. Trend monitoring can
be very helpful in these situations. Be aware
that one engine could have cooled down due to
an ITT problem, so don’t assume the warmer
engine is the culprit. A change in ITT of 20
degrees or more should be investigated as soon
as possible to avoid possible damage to the
engine. As a rule of thumb, if the ITT and fuel
flow indications have increased and the N2 has
decreased at Take Off N1 of the day, there is
most likely a problem in the hot section area. If
the ITT, N2 and Fuel Flow have all increased at
Take-Off N1 of the day, then a problem could be
in the cold section or HP Compressor area. Be
sure to consult the appropriate maintenance
manual for troubleshooting procedures.
Trivia Question
— Dan Arrick
The previous question was: What is the
purpose of the cold or hot nozzle installed on a
JT15D?
The answer: The selection of different size
cold or hot nozzles provides a means of adjusting
each engine to produce a known given thrust for
a specific N1 speed (i.e. N1 vs. thrust).
This edition’s question is: What changes
will you see in ITT, N2 and Fuel Flow
indications if high turbine tip clearances are
excessive?
The first 10 callers with the correct answer
will receive a small prize. Please respond to
Dan Arrick by phone by calling
800.525.2376.
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