JT8D Engine Maintenance
Revised 28-Feb-2001
Back To Index

This is just a broad outline of maintenance concepts of the JT8D.

When maintaining the engine you will be using the following documents for reference

Maintenance Manual (MM)
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 maintenance
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 engine models.
Airworthiness Directive
Is 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.

Hard Time
These are fixed time intervals when specific items are inspected or replaced a typical example would be

Check A Basically a visual inspection
Check B Filter inspections / replacement
Check C Hot section inspections / SB 6038
Check D Heavy Maintenance


Hot Section Inspection (HSI)
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.

On Condition
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.

Inspection Aids
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.
Chip Detectors
Magnetic plugs located in the oil return line that capture ferrous metals.
Filters in fuel, oil and air systems to capture contaminants.
Self Explanatory
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.

Tracking Hours & Cycles

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.




Back To Index