PT6A engines maintained under the Maintenance On Reliable Engines (MORE) Instructions For Continued Airworthiness are separated into modules for record keeping purposes.  Experience has shown that some portions of the PT6A engine need inspection / repair more often than other portions.  The purpose is to allow each module to be repaired or overhauled when appropriate and when the remainder of the engine is operating normally to allow the remainder of the engine in service until there is a reason for it to be repaired or overhauled.

The record keeping modules in the MORE Instructions For Continued Airworthiness are:

Accessories

Compressor Module

Hot Section Module

Power Section Module

Example: An engine with 4000 hours TSO experiences a lightning strike.  The Power Section Module will require repair but the owner decides to overhaul it instead.  The Power Section Module will then have 8000 hours before overhaul is required again.  At that time, the other three modules are removed for overhaul, but the Power Section Module will not need overhaul since it has 4000 hours to go before next overhaul.