I hear this repeated many times to pilots. As a mechanic, it applies to me, too. One thing I want to bring everyone’s attention to, so everyone is aware, is that there have been some changes to the Pratt & Whitney Canada manuals that could directly affect you.
First, when changes are made to the manuals, you can grab a quick overview of what was updated. When you open your manual, and look at the chapter list, there is a section called highlights. This section gives quick details of what has changed. If you are using the customer portal, it also includes hyperlinks to each change for your review.
Many maintenance manuals have recently been updated. For the purpose of this discussion, I am looking at the manual for the PT6A-34AG Manual 3021242 Issue 72.0. This particular manual and several others were updated in January 2024. The revision includes incorporating several service bulletins, additions to lubricate specific areas after washing, and some inspection procedures for fretting on fuel nozzles.
The biggest change, in my opinion, has to do with changes in prop strike and sudden stoppage inspection. Pratt & Whitney Canada has now provided a very detailed description and a decision tree for determining the level of maintenance required. This includes props striking the ground or striking a wire at speeds above and below flight idle. These factors go into the level of maintenance required.
If you had a strike, here are some additional changes. As part of the inspection, if any damage is found to the inlet case struts, accessories, reduction gearbox or accessory gearbox housings, if any components sheared or separated from the engine, or if foreign object or metallic debris is found in the engine, a specific disposition or additional parts replacement must be determined and provided by Pratt & Whitney Canada. The initial first step of the inspection should be the completion of the Service Information Letter (SIL) Gen-135. This report describes the incident and helps the repair shop determine how to get the engine back in the air as quickly and safely as possible. Please let me know if you need help locating this SIL or completing it. I am glad to help. Pictures of the airframe and any engine damage are also very helpful.
Once you go through the on-wing inspection and determine that you must send the power section or engine in for repair the manual changes have not stopped. When we receive a power section or engine for prop strike/sudden stoppage repair, the overhaul manual also has some revisions. Using the PT6A-34AG Overhaul Manual, 3021243 Revision 51, dated November 27, 2023, the entire prop strike and sudden stoppage section has been revised. Again, it starts by saying that the shop may need a SIL Gen-135 to determine the proper work scope. If you already completed this step, it will help save time, which can be critical.
We will follow one of two charts in the shop based on the incident. The first is another decision tree which steers us to the proper level of inspection required. The second is a table to advise us on how to treat each component of the power section/engine being repaired. The manual requires mostly visual inspection for the gas generator unless specific damage is noted or witnessed. Most of it has to do with rubbing, scraping, or binding. The power section inspection is where the biggest changes have been made.
Almost all the components of a power section now require a full overhaul level of inspection. This includes non-destructive testing and measuring. This is a change from the visual inspection requirements on some components. The propeller governor and overspeed governor also must be submitted for an overhaul. The biggest change and potentially costliest is the automatically rejected parts. We all know from years of experience that the #6 bearing on a small PT6 is an automatic replacement item. This hasn’t changed. However, the propeller shaft and the #5 bearing are now on the list of items automatically discarded. These three components can add up to a significant amount. There also could be delays in procuring these parts, as more shops will need them. The large PT6 instruction may allow inspection of some of these components but could also include discarding the #7 bearing.
Potentially, there is help. If you choose to use a shop that is part of the Pratt & Whitney Canada network, some additional cost-saving measures may be available. It has been discussed at several events that the parts identified above may have support available. Potentially, new parts could be priced below overhaul-condition parts. I always encourage everyone to take full advantage of anything Pratt & Whitney Canada offers at a great discount. Please have this discussion with your Designated Overhaul Facility or Field Service Manager if you have a prop strike.
Not everyone is aware but there is also a requirement to perform a test cell run after repair of the power section. Historically, we have received a waiver from engineering that allows us to perform this run on wing. That isn’t a guarantee as now engineering is reviewing the parts replaced within the power section before determining test cell or not. Sometimes, we have a gas generator that we can use for the testing purposes of the power section, but in some cases, we ask that the complete engine be sent in. Even if no work is required on the gas generator, we will need it to perform the testing.
Robert Craymer has worked on PT6A engine 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 as well as being an instructor of PT6A Maintenance and Familiarization courses for both pilots and mechanics. Robert has been elected to the NAAA board as the Allied-Propulsion Board Member. Robert can be reached at robertc@covingtonaircraft.com or 662-910-9899. Visit us at covingtonaircraft.com.
