NTSB Reports | Accident Synopses

CRAYMER’S COUNSEL

Robert Craymer - robertc@covingtonaircraft.com

AD 2022-08-13

When Transport Canada issued AD CF-2019-30R1 in December of 2019, discussion began if/when the F.A.A. would issue a corresponding A.D. That day has officially arrived. The Federal Aviation Administration has now issued A.D. 2022-08-13. This AD applies to PT6A-34, -34B, -34AG, -114 and -114A engines. Meaning, that for the ag aviation industry, if you are running a PT6A34 or -34AG, this A.D. could affect your engine. If you are operating any of these engine models, here is the information that you need to know.

A.D. 2022-08-13 deals specifically with a repair that has been performed on compressor turbine vane rings (CTVR) by Southwest Turbines Inc. The repair of the CTVR is identified as repair process number S.T.I. 7250-254. Vane ring part numbers affected are 3029051, 3032151 and 3123001. If you have one of these vane rings repaired by this specific repair, you have 250 hours or 270 days from May 27. That’s February 21, 2023, or 250 flight hours, whichever comes first, to comply with A.D. 2022-08-13.

The first step to identifying your potential exposure is to review your engine logbooks. Find the entries where you had hot section inspections or other gas generator work performed. If your vane ring was replaced, it should be identified in those entries. If your entry identifies a vane ring change or repair, investigate the rest of your records. Your mechanic will often supply you an 8130-3 for major components, like the CTVR. This 8130-3 will include the company’s name that worked on the vane and what repairs were performed. This is where the specific repair (S.T.I. 72-50-254) should be identified. Other times your mechanic will have a record of the work performed, such as a work order number. They may have records there to help you. You may need to follow up with the mechanic/shop that performed the work where the vane ring was repaired/replaced. The information you need should be out there and available. If you exhaust every other means of determining what is in your engine, the alternative is to split the engine and identify what CTVR is in your engine. With the part number and serial number, you may have to contact Southwest Turbines Inc. and have them identify if your vane ring was repaired with repair S.T.I. 72-50-254.

The next subject of the A.D. identifies specific compressor turbine blades that will require replacement. The A.D. calls out CMSX-6 compressor turbine blades. CMSX-6 are the Pratt & Whitney Canada single crystal blades introduced starting with service bulletin 1690, with the latest version of these blades being released by service bulletin 1767. If you find that you have operated an affected CTVR and you have one of these sets of blades, the blades will require replacement along with the vane ring.

Now you have identified that the engine’s vane ring and compressor turbine blades need to be replaced per the A.D., what do you do?

We reference back the engine maintenance manual. When replacing a compressor turbine vane ring, there are directions one must follow. The maintenance manual states: “If stator assembly must be replaced, an assembly of same class or ± 0.03 in² or ± 0.12 class (REF. S.I.L. No. GEN PT6A 020).” This is where things might get sticky. When it comes time to locate the replacement vane ring, getting a like flow class is paramount. The vane ring flow class has the potential to alter your engine performance. A smaller vane ring class accelerates the air more, increasing the compressor speed (Ng). A higher Ng speed provides more air to the engine, more cooling, and a lower I.T.T. That sounds great, doesn’t it? What if your engine is already pushing up against the redline on Ng? ➤