SL2023-740/JNN Overspeed

This service letter contains important information concerning recommended inspections to be carried out on engines in the unlikely event that an uncontrolled overspeed incident has occurred.
Engine over speed can be categorized as follows:

1. Controlled overspeed, the engine has been stopped by the overspeed protection device. This is usually set to stop the engine at rated speed X 1.15%, e.g. during the overspeed test carried out in connection with the quarterly test of the engine’s safety equipment.

2. Uncontrolled overspeed, is defined as any engine speed >1.25 X rated speed, independent of the duration.
If it is not possible to determine the engine’s rpm level during the overspeed incident, it is considered to be an uncontrolled overspeed incident and the precautions in this service letter must be followed.

NOTE:
Before any attempt to restart the engine after an overspeed incident, the reason for the overspeed must be identified and rectified.