When to order an engine mount replacement

By: Kevin Ensminger - Learjet Service Engineering

Effectivity: Learjet 40, Learjet 45 and Learjet 70, Learjet 75 aircraft 

ATA 71 - Power Plant 

March 8, 2022

Bombardier would like to remind its Learjet 40 and Learjet 45 and Learjet 70 and Learjet 75 aircraft operators that due to increased parts demand for forward and aft engine mount isolators at the required replacement interval, it is important to plan accordingly and ensure parts are ordered prior to the event. 

Honeywell previously increased the Major Periodic Inspection (MPI) from 3,000 to 3,500 hours and the Compressor Zone Inspection (CZI) from 6,000 to 7,000 hours for qualified engines. The Lord Corporation (Parker) engine isolator mounts (forward and aft) were assessed prior to this escalation and approved for a finite maximum replacement interval of 6,000 flight hours, with a mid-life inspection occurring at 3,000 hours to coincide with the CZI and MPI (respectively) at the time. 

For engines qualified for the new MPI/CZI intervals, a new replacement schedule IRN was created, requiring the forward and aft engine mount isolators (bonded mount/aft mesh assemblies) to be replaced at the 3,500-hour interval. This reduced replacement interval is to prevent an out of schedule engine removal to replace the isolator mounts prior to the CZI off wing event, as the mounts have not been approved to exceed 6,000 hours. 

For engines with the escalated MPI/CZI and 3,500-hour mount replacement requirement, please ensure that parts orders are placed well in advance of the engine maintenance intervals in case of higher-than-normal lead times. Learjet is currently working with the supplier to increase production, satisfy demand and build adequate stock margins. 

For additional information or questions, please contact your regional Field Service Representative or the Customer Response Centre.