PT6 Hot Section Inspections
Some additional helpful tips from the field
By Kelly M. McCallum
In July’s issue of AMT, the Turbine Technology article on PT6 hot section inspections provided several helpful tips on performing the PT6A engine hot section inspection. Following are a few more recommendations/tips from Mr. Kelly M. McCallum, Manager, PT6A Engineering and Service Centre at StandardAero VOF in Tilburg, The Netherlands, that should prove to be beneficial to technicians who service this engine model. As a result, component life may be extended, meaning lower direct operating cost to the end user.
Unscheduled hot sections
If the hot section inspection you are performing is unscheduled due to performance related concerns, please 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 the unscheduled inspection. As indicated in the July article, 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. A faulty accessory or airframe system can often be quite easy to repair, and can save several labor dollars, which do not need to be invested in splitting an engine, just to find that there is nothing wrong internally.
Thorough turbine rinses
Compressor washes are carried out by most operators on a regular basis, using the solution specified in the related maintenance manual. There is, however, a tendency for some operators to not perform a turbine rinse after the compressor wash. Try to get into the habit of always rinsing the turbine after a wash with solution. 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 the 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. Advanced sulfidation (attack of the blade coating) can be attributed to several factors. If operating your aircraft in an area with high amounts of atmospheric pollutants, or close to salt water, then turbine washes may even be performed on a daily basis to slow any attack.
Know your service bulletins. In particular, all technicians 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.
The small series PT6A engine (such as –20, 27/28, 34, 114, 135) has a life limit (TBO consideration) on the compressor turbine blades. Please ensure that the CT blades are not due for overhaul (which includes fluorescent penetrant inspection, blade stretch and coating inspection etc.) at the time the hot section inspection is being performed. Per the current and applicable Pratt & Whitney Canada (P&WC) instruction, small series engine CT blades can be run for 3,000 hours from the time of full overhaul, or 5,000 hours from the time installed new. With some operators running extended TBO’s on their engines, this should be monitored closely for compliance.
This 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...
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