Honeywell Bimodal Service Bulletin Update

May 2022

Honeywell has issued Revision 3 of SB (Service Bulletin) AS907-72-9084, Reduced Time Interval for Oil Filter Replacement or Engine Fault Diagnostic Data (EEI) Download to Provide Enhanced Monitoring of Aft Sump Components.

For operators in compliance with the CAMP trend monitoring of the ECU (Electronic Control Unit) downloads every 25-35 days, the shortened oil filter analysis interval of 150-250 hours is no longer required and the oil filter analysis should return to the interval as outlined in the applicable engine LMM Chapter 5 periodic requirements. For operators not participating in the CAMP trend monitoring of the ECU downloads every 25-35 days, Honeywell recommends the 150–250 hour shortened interval oil filter analysis continue as outlined in the previous revision of service bulletin AS907-72-9084.

Honeywell’s investigation into the aft sump issue has been resolved with the installation of a new #4 carbon seal as implemented in Service Bulletin AS907-72-9094. Once SB AS907-72-9094 is complied with, the 25-35 day ECU CAMP trend monitor download requirements may return to the interval as outlined in the applicable engine LMM Chapter 5 periodic requirements and AS907-72-9084 requirements are no longer applicable.

Honeywell SB AS907-72-9084 was introduced for recommended trend monitoring of the non-bearing components in the aft sump of all Honeywell AS907 series engines for early detection of an impending aft sump issue. This SB was initially released in June 2019. The aft sump issue that is identified by the proactive trend monitoring per AS907-72-9084 is referred to as Bimodality.

In conjunction with Service Bulletin AS907-72-9094 for installation of the new #4 carbon seal, SB AS907-72-9080 and SB AS907-72-9045 are also incorporated if it is discovered through logbook research that the engines qualify and they have not been previously complied with. These related SBs will be incorporated at the time of a bimodal event since access necessary for completion will occur. SB AS907-72-9080 is the replacement of the #4 bearing. SB AS907-72-9045 is the installation of improved annular ball bearing (tower shaft bearing).

Bimodal events can be accomplished by a Honeywell Authorized Minor Level Service Center, such as Duncan Aviation. The #4 carbon seal and related SBs will be performed on wing with the engines remaining installed on the aircraft. This maintenance can be accomplished on the road at your hangar or any of Duncan Aviation’s full-service locations.

If you have questions about bimodality or Service Bulletin AS907-72-9084, call Shawn Schmitz, Engine Tech Rep., at +1 402.730.8767 or email: Shawn.Schmitz@DuncanAviation.com.

To schedule your bimodal event with Duncan Aviation, don’t hesitate to call me.

To learn more about previous revisions to Service Bulletin AS907-72-9084, read this Duncan Intelligence article: https://www.duncanaviation.aero/intelligence/2020/June/honeywell-service-bulletin-as907-72-9084-and-bimodal-events