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The Service Bulletin

In a conversation last week with Pratt & Whitney Canada, the topic of the “Know My PT6” app came up. While discussing the app, it was stated that inputting your aircraft/engine details will provide you with information specific to your operation. One of the things the app highlights for you are service bulletins categories 1 through 3. It doesn’t give you full access to these service bulletins, but it does call out important issues that could affect your engine. It got me thinking, does everyone understand what service bulletin categories represent?

Service bulletins are issued for a variety of reasons. Parts upgrades or changes, material changes, use of specific consumable materials (i.e., fuel or oil), and cycle tracking are just a few things brought to us by the service bulletin. If a critical situation arises, Pratt & Whitney Canada will send out an alert service bulletin highlighting an important change.

Service bulletins are prioritized by a category number between 1 and 9. Categories 1 through 3 are service bulletins that must be done before the next flight, the next maintenance procedure, or before a specified number of hours or cycles. For instance, service bulletin A1742 was issued for the PT6A-34AG in April 2014. This alert service bulletin required compressor turbine blade inspection or replacement for a specific group of engines. The SB had a category 1 component, meaning it must be done before the next flight. It also had a category 3 component which provided an hour limit that had to be adhered to. This category of service bulletin is one that Pratt and Whitney Canada relies on their Field Service Managers and their engine shop partners to make sure the information is distributed. The “Know My PT6” app alerts you to this type of information.

The next grouping of SBs is Category 4 through 6. These service bulletins, for the most part, pertain to engines being worked on in a shop. Many of them pertain to parts or assemblies in the engine that can only be accessed by disassembling an engine that is not performed outside the shop environment. For example, service bulletin 14377, the latest revision in August 2021. This SB is for some -60 series engines that include the PT6A-67AG. It is a Category 6 service bulletin; Pratt & Whitney Canada recommends doing this SB when the sub-assembly is disassembled to access the affected part. In this case, the power turbine shaft housing. That is not a part that is accessible except in a shop environment. One other topic of note in this service bulletin is that the manufacturer is also providing an additional price reduction on this part if you choose to follow the guidance and replace it. This is done through commercial support programs or CSPN. These programs are typically for a limited time and allow additional discounts on new parts from Pratt & Whitney Canada.

The final groupings of service bulletins are categorized from 7 through 9. These categories usually contain changes caused by supplier changes, operator concerns or other changes. Some of these changes include airframe manufacturer-requested changes or governmental changes. Service Bulletin 13526, issued in November 2021, is an example. This SB is a Category 7 for some 60 series engines, including the PT6A-65AG. There is a component within the engine that is chrome plated. Due to new standards of the “Registration, Evaluation, Authorization and restriction of Chemicals” (REACH) regulations, there is a replacement component available that is not chrome plated. Pratt & Whitney Canada recommends replacing the old part once the supply has run out. This means that new engines will come with the new part installed, and they will no longer sell the old part.

P&WC Service Bulletin Categories:

Category 1 P&WC recommends to do this service bulletin before next flight

Category 2 P&WC recommends to do this service bulletin the first time the aircraft is at line or  maintenance base that can do the procedures

Category 3 P&WC recommends to do this service bulletin with ____ hours or ____ cycles

Category 4 P&WC recommends doing this service bulletin the first time the engine or module is at maintenance base that can do the procedures, regardless of the scheduled maintenance action or reason for engine removal

Category 5 P&WC recommends doing this service bulletin when the engine is disassembled, and access is available to the necessary subassembly

Category 6 P&WC recommends doing this service bulletin when the subassembly is disassembled, and access is available to the necessary part

Category 7 You can do this service bulletin when the supply of superseded parts is fully used

Category 8 This service bulletin is optional and can be done at the discretion of the operator

Category 9 Spare Part Information


That is a brief and “simple” look at how service bulletins are looked at. Occasionally shops give you recommendations on SBs, such as doing all categories 1 through 6 during a repair or overhaul. This is a baseline of service bulletins and doesn’t usually amount to much change as the bulk of these have previously been complied with during your engine’s life. Discuss with your shop or your Pratt & Whitney Canada Field Service Manager about service bulletins that might be good for you to comply with. Check in on your “Know My PT6” app occasionally to see if any changes have occurred to the engine models you operate. Let me know if I can ever help.


Robert Craymer has worked on PT6A engines and PT6A-powered aircraft for the past three decades, including the last 25+ years at Covington Aircraft. As a licensed A&P mechanic, Robert has held every job in an engine overhaul shop and has been an instructor of PT6A Maintenance and Familiarization courses for pilots and mechanics. Robert can be reached at robertc@covingtonaircraft.com or 662-910-9899. Visit us at covingtonaircraft.com.





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