Air System
TROUBLESHOOTING PROCEDURES
All personnel should clearly understand that
Troubleshooting procedures are similar in
any obstruction or interruption of the air as it
practically all applications. Troubleshooting is the
moves through the engine will affect the entire
logical or deductive reasoning procedure used
operation of the engine. Entrance of foreign
when determining what is causing a particular
matter into the air system is one of the main causes
system malfunction. There are six steps involved
of service trouble. As the foreign matter passes
in good deductive troubleshooting.
rearward, it causes improper combustion, block-
age of cooling air passages, and combustion
1. Conduct a visual inspection. This inspec-
section damage. The turbine section and the after-
tion should be thorough and searching. Check
burner section may be damaged.
all lines, units, mechanical linkages, and parts
for evidence of leaks, looseness, material
Compressor Section
condition, and proper installation. During this
visual inspection, check all systems for proper ser-
The compressor section of the turbojet engine
vicing. Check reservoirs for proper servicing
is subject to a variety of service troubles from
levels, accumulators for specified preload,
foreign matter passing through the compressor.
etc.
Small pebbles, nuts, bolts, and washers can cause
damage to the compressor rotor blades and stator
The aircraft discrepancy book (ADB) and the
vanes. Damage severe enough to warrant complete
visual information display system/maintenance
overhaul of the engine may result from the inges-
action forms (VIDS/MAFs) are invaluable
tion of foreign matter.
troubleshooting tools. The type of flight and
previous maintenance actions may give an
Combustion Chamber and Turbine Section
indication of the engine's problem. You may
save many man-hours of troubleshooting an
High temperatures take place in the combus-
engine discrepancy by first screening the ADB
tion and turbine sections. Few major service
for prior maintenance. You may find prior
troubles occur when maximum temperature and
maintenance that has contributed to the cause of
maximum rpm limits are closely monitored. Hot
the new problem. You may find improperly
starts, overtemperatures, and exceeding maximum
performed maintenance, and trends of prior
rpm will cause extensive service troubles in the
malfunctions.
combustion and turbine sections.
2. Conduct an operational check. Check the
Fuel System
malfunctioning system or subsystem for proper
operation. This includes checking the mechanical
The fuel system of the gas turbine engine
movement of throttles and linkages for the
begins at the engine-driven fuel pump. The system
correct movement without binding. Check for the
proper sequence of operation and speed, and
ends with delivery of fuel to the combustion
whether a complete cycle was obtained. Some-
chambers through fuel nozzles in the form of
highly atomized spray. Common service troubles
times an operational check requires special test
are wrong types of fuel, water or other foreign
equipment or engine turnup to check out the
matter in the fuel, defective fuel-boost pumps, and
system properly.
clogged fuel filters.
3. Classify the trouble. Malfunctions usually
Lubrication System
fall into four basic categories. They are the
hydraulic, pneumatic, mechanical, and electrical
groups. Using the information gained from steps
The proper grade of oil and cleanliness when
1 and 2, you must determine under which
replenishing the oil supply are absolute require-
classification the malfunction occurs. Something
ments to avoid lubrication system troubles. Gas
turbine engines have few moving parts, but the
affecting normal flow of fluid would be classified
speed at which the parts move, especially the
under the hydraulic classification. The flow of
fluid may be affected by external and internal
rotor, requires constant lubrication to the bear-
leakage, total or partial restriction, or improper
ings. Oil starvation for a short period of time can
lubrication.
result in having to remove the engine for overhaul.
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