Does your engine have a time when it sits unused? Are you properly preparing to let it sit on or off the airframe?
Like any machine, the times the PT6 engine is not used can be just as hard or harder on it than the times when it is being used routinely. Pratt and Whitney Canada has given us some very easy-to-follow guidelines that will make sure that when you are ready to work, your engine is as well. Everything regarding preservation is scheduled around a time frame and has significant consequences. If an engine is not preserved per the published schedule, the engine could suffer corrosion damage, and the warranty could be voided. The only way to check for corrosion damage is to disassemble the engine to visually inspect ALL components. Therefore, we always provide time to discuss the importance of engine preservation.
Here is what you need to know:
If the engine will be inactive for 0 to 7 days, all that is required is to make sure that the engine is sheltered. Humidity and temperature changes that can cause condensation are grounds to move your preservation plan to the next level. Also, if there is a lot of salt in the atmosphere you live in, you want to do a clean water rinse (desalinization wash) prior to storing the airplane. Exhaust covers, inlet covers and securing the prop are really the only other requirements.
The second calendar interval classification is 8 to 28 days. This area of the calendar is the most common in ag aviation. The first step is to run the engine and follow the 0 to 7-day instructions. Next, you will need to add desiccant bags and a humidity indicator in the exhaust duct. The objective is to maintain and confirm the humidity level at 40% or less. Check the humidity indicator every couple of weeks; replace the desiccant and indicator if it turns pink. Make sure there is no source of humidity near the engine, and if there is, make sure to remove it.
If your time dictates that your engine must sit for 29 to 90 days, there are a couple of additional steps to take. Washing the engine inside and out, touching up any of the missing protective coatings and lubricating the linkage. Next, disconnect the fuel supply line and cap at the oil-to-fuel heater. Disconnect the fuel line at the flow divider inlet and then add the proper preservation oil. Instructions in the maintenance manual show you how to do a motoring run to replace the fuel in the system with the preservation oil. Then, of course, you cap and cover everything. Make sure that you also follow the 0 to 28 days steps, and don’t forget your humidity indicator.
For some, the engine may sit over 90 days. For those, you must do all the above plus drain the oil, remove the oil filter and coat the flanges and other exposed surfaces with either oil or a preservation compound as described in the engine maintenance manual. Add a tag to your oil filler cap advising that the oil has been drained and include the preservation date. If you expect the engine to sit for longer than a year, the best practice is removing it, doing all the above, and storing it in a proper shipping container.
What happens if I don’t?
If your engine is not preserved 8-28 days before starting, you must do a Total Acid Number test on the engine oil. Up to 90 days, there are numerous other things you must check and do, as well as specific start-and-run procedures. If your engine goes up to a year unpreserved, fuel nozzles, accessory bench checks and additional inspections are required. In addition, the engine must be disassembled and inspected for corrosion.
The easy alternative is to run the engine weekly. That may seem like a nuisance, but maybe not when you compare it to the cost of parts replacement or downtime for inspections. When you perform these runs, you want to run at 80% power for 10 minutes, reducing the oil system's condensation and preventing fuel stagnation.
Remember that if you don’t record the work you do to preserve your engine in the engine logbook, it doesn’t happen. Engine preservation must be documented. All of this is especially important if you have a Pratt & Whitney Canada warranty on your engine. You don’t want to jeopardize your warranty claim because the engine wasn’t preserved or stored correctly.
As always, I just want to provide you with the best practices to allow the engine to run trouble-free for the longest possible time. Take as much time to protect your engine as you do protecting yourself, and your engine will be there for you when you need it.
Robert Craymer has worked on PT6A engines 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 and is 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.
