PT6 Hot Section Inspections: Some tips from the field

Editors note: The following article on PT-6 hot section tips was written by Standard Aero's Kelly M. McCallum, and originally ran in the September 2001 issue of AMT. Due to several reader inquiries on the article, we have decided to feature it again as a resource for those performing hot sections on these engines.

Unscheduled hot sections

If the hot section inspection you are performing is unscheduled due to performance related concerns, ensure that the airframe systems such as the ITT indication system and the torque meter system are calibrated properly prior to splitting the engine. You may also want to confirm by borescope inspection of the hot section that there is damage that would warrant an unscheduled inspection. Bleed valves should be checked for correct operation if suspected to be faulty. Approximately 75 percent of the time, a sudden shift in a trend cannot be attributed to hot section deterioration.

Thorough turbine rinses

Compressor washes should be carried out on a regular basis, using the solution specified in the related maintenance manual. There is a tendency for some operators to not perform a turbine rinse after the compressor wash. If you don't perform this rinse, the corrosive solution that is pulled through the compressor to the hot section area during the wash will sit and corrode the turbine blades. Don't assume that a water rinse through the compressor will remove all of the solution from the turbine area.

If the compressor turbine (CT) blades show evidence of sulfidation (in particular, stage 2) during the hot section inspection, and are deemed to be acceptable for reinstallation, ensure that turbine rinses are subsequently performed on a regular basis. If operating your aircraft in an area with high amounts of atmospheric pollutants, or close to saltwater, then turbine washes may even be performed on a daily basis to slow any attack.

Service bulletins

Know your service bulletins. You should be aware of which SB's affect the engine's life-limited components, and which cover the engine time between overhaul (TBO) considerations.

Cycle/life limits

When re-installing the compressor turbine (CT) or power turbine (PT) after the individual component inspection, ensure that there are enough cycles remaining on the component to make it to the next scheduled inspection interval. If there aren't enough cycles remaining, then this should be flagged in the engine logbook so that the turbine will be removed when it reaches its life limit.

CT vane ring burning/material loss

The P&WC maintenance manual states that burning/material loss at the trailing edge location of the CT vane ring is unacceptable, and that the vane ring will require replacement due to this condition. Please note that if this condition exists, it is recommended that a designated overhaul/repair facility be contacted for evaluation assistance. This is important, as a set of turbine blades that have been run behind a vane with material loss beyond P&WC Overhaul Manual limitations will require replacement due to excessive blade cyclic loading. The hot section may, therefore, have to be shipped to an authorized repair facility to perform this blade replacement.

Oil filter and strainer

Try to get into the habit of checking the engine oil filter along with the RGB strainer. My recommendation is to perform these two checks at the beginning of the inspection. Performing a full hot section inspection on an engine that may be making metal would not prove to be cost-effective. This is also a good time to see if your engine oil filter requires replacement due to life limitations.

Compressor blade damage

When checking your first stage compressor blades for erosion, etc., ensure that there is no foreign object damage (FOD) that may not be allowable per the maintenance manual criteria. If you don't do this, you could waste money and time if you start the hot section inspection, only to find out later that the compressor blades are damaged beyond limits and the engine needs to be removed from the airframe.