For PT6 engines, general MRO practices should be performed regularly, while a total overhaul of the turbine will vary on timing, depending upon usage and other factors that can affect wear and tear on the engine. However, while a total overhaul should be handled by a DDOF for optimal aircraft support, pilots and owners should engage in basic maintenance routines for safety and performance.
Basic maintenance will include inspection and cleaning of:
- Fuel nozzles
- Fuel pumps
- Oil pressure pumps and lines
As a result, focus will also need to be on the separate parts of the PT6 engine, specifically:
- Propeller shaft
- Power turbine
- Hot Section
Covington Aircraft recommends an initial fuel nozzle service interval of 200 hours. Once you become familiar with the flow checks and how your nozzles perform under normal conditions, you can extend that time to around 300 hours if desired. Pratt & Whitney recommends a fuel nozzle service interval every 400 hours, but in our experience, anything over 300 hours requires heavier maintenance. Streaking fuel nozzles are one of the major causes of damaged hot section components, especially the combustion can liner and compressor turbine vane. Pay attention to your fuel nozzle service interval times and you’ll increase the life of your hot section.
Oil maintenance tends to be one of the easier routine tasks, as this can be accomplished through visual inspection of the dipstick and manual addition of oil in order to reach the appropriate level. It is important that oil checks and replenishment are performed at least 15 minutes after the engine has been shut down, as this allows for cooling and viscous contraction. Total overhauls can include a systems flush for the oil as well, but these are performed at designated MRO facilities.
Along with replenishment, oil maintenance should also include a check of the filter to discern any debris that may have been captured and, when necessary, to replace the old filter. Excessive debris in the oil filter can be an indicator of the need for a systems flush, and this can also improve the longevity of the new filter. The oil sample should also be periodically submitted to a lab for analysis, as this can uncover issues that may affect performance.
PT6 engines also utilize an RGB chip detector that needs to be maintained. Visual inspection of the chip detector housing and the part itself can indicate if there are any issues that could precipitate a replacement. It should be noted that in changing the chip detector, the oil will drain from the engine, as there is no self-closing valve.
Compressor maintenance is a further concern that can impact both performance and safety. Routine desalination and washes for the engine, compressor, and turbine should be scheduled to ensure higher engine power and consistent function. Although the timing for these flushes can vary, it is generally recommended that they are done every 10,000 nautical miles.
Fuel nozzle cleaning and replacement is another major maintenance that should also have a regular routine and can improve performance and safety. Since PT6 engines can have either simplex or duplex nozzles, it is important to identify the type of part with inspection, as simplex nozzles are two different parts, while duplex are identical. This can also make it necessary to adhere to removing and cleaning one nozzle at a time, in order to avoid confusion when replacing parts.
Although PT6 turbines do not require the same amount of attention to lubrication as radial engines, bearings and moving parts can succumb to wear and tear. When performing engine maintenance, it should also be noted that smaller models will present with only two bearings in each of the segments of the engine, while larger models have three bearings in the propeller shaft. Checking lubrication and packing bearings will enhance the longevity of all the moving parts.
This type of basic maintenance in between total overhauls and scheduled MRO services will not only keep the PT6 engine performing at its best, but can also ensure better safety from the quality turbine.