This is just a broad
outline of maintenance concepts of the JT8D.
When maintaining the engine you will be using the following documents
Contains approved and recommenced maintenance procedures normally
performed on line for an installed engine. Its constructed in the ATA
system with the following elements
Chapter / System, Section / Subsystem, Subject / Unit. I will not cover
those items here but give it it's own section at a later date.
Engine Manual (EM)
Contains approved and recommenced procedures for uninstalled engine
Illustrated Parts Catalogue: (IPC)
Contains lists and illustrates all saleable engine parts.
Standard Practices Manual
Approved and recommended standard practices, information, instructions
and frequently used procedures.
Service Bulletins (SB)
Provide information or instructions as required for modifying or
replace parts to the later configuration.
Alert Service Bulletin (ASB)
Advanced information or instructions on specific component problems
and the actions planned or in the process to correct the problem. Alert
SB's are on blue paper and is issued in advance of a service bulletin.
Support Equipment Numerical Index (SENI)
Lists all the engine service, maintenance and overhaul tooling for
each level of maintenance.
Spare Part Bulletins
Provides information on introduction of new parts replacing previous
parts, spec changes to spare parts, or discontinued spare parts on specific
issued when products in which the controlling authority has found an unsafe
condition. It prescribes inspections, conditions and limitations, if any,
under which those products may continue to be operated. No person may
operate a product to which an airworthiness directive applies except in
accordance with the requirements of that airworthiness directive.
First thing is to
define the objective. The purpose of it, is to check the condition of
a part and repair or replace it as necessary. This is done in a variety
of ways, every operator is different but the purpose is still the same
as described in the definition above.
These are fixed time intervals when specific items are inspected
or replaced a typical example would be
a visual inspection
inspections / replacement
section inspections / SB 6038
Hot Section Inspection
The engine is removed from the aircraft. The combustion chamber area and
high turbine area are inspected and repaired, the engine is then reinstalled.
Schedules vary can be between 4,000 and 8,000 hours.
Heavy Maintenance (Overhaul, HM)
Engine is removed and sent to the shop where a complete inspection is
made and repairs / replacements as necessary.
This utilises engine data taken by the flight crew during cruise
or by maintenance on the ground, automatically or manually. A maintenance
engineer adjusts the data and compares it against a baseline to form deltas
to allow detection of engine malfunctions. Maintenance is then scheduled
as per the direction of the trend analysis.
Spectrum Oil Analysis Program (SOAP)
An oil sample is taken from the engine and sent to a lab where it is spectrographically
analysed. Any metal is detected by type and count. A good man will even
tell you the bearing it came from, great deal of skill required.
Magnetic plugs located in the oil return line that capture ferrous metals.
Filters in fuel, oil and air systems to capture contaminants.
Bit like X Ray (I'm no NDT expert, anybody out there want to write something?)
A probe with mirrors, prisms or fibre optics for looking inside the engine.
Normally considered as the time the aircraft leaves wheel chocks
to return to wheel chocks.
Operating the engine from idle to high power and return to idle. Most
operators consider a cycle from take off to landing.