PT6 MAINTENANCE
March 15, 2023, By PT6 Owner and Operator Steve Wightman.
BRIEF HISTORY. “In December 1963, P&WC shipped the first PT6 production engine, the PT6A-6, to Beech Aircraft Company for its Beech 87, which later became the King Air. The PT6A-6 was a highly innovative gas turbine that represented a significant advance in technology from the traditional piston-driven engines used to power small aircraft. Gas turbines have a higher power-to-weight ratio than piston engines.” https://www.pt6nation.com/en/articles/article/best-of-the-pt6-nation-the-legend-tells-its-story/.
Safety by the numbers. Here are the simple facts. Since 1995 there have been over 20 Seawind accident fatalities and many others nonfatal. Score 100% piston engines. 0% turbine engines. Which are safer to fly? Go figure.
In 2008 I was the first ever to install a PT6 on a single-engine amphibian. The choice between a PT6 and a piston IO-540 was easy. Further, the IO-540 has a take-off RPM of 2700 V. 2200 for the quieter PT6. The cruise RPM is also a much quieter 1900 RPM. Safety and reliability is legendary. The PT6 series has accumulated over 1 billion hours of flight. Used by governments worldwide and major airplane manufacturers as the engine of choice, it boosts millions of hours of fault-free flight.
Price. With twice the TBO of the IO-540, (1800-2000 hours) the factory overhaul cost is currently about $71,743 X 2 = $143,486 every 4000 hours. http://blog.overhaulbids.com/lycoming-540-overhaul-cost/. Contrast that with a cost of $160,000 – $235,000 at PWC. In sum, I got a much better turbine engine at competitive prices. It is worth saying here that overhaul prices vary depending on the engine condition, records, inflation, shop geography, turnaround time, and accessory repairs or replacements.
Further, the cost of my used PT6A-20 with a new MT propeller and a new airframe-mounted electric fuel pump, $119,000, was significantly lower than a new IO-540 with no Prop, no accessory option. Math complete, even comparing a used Lycoming engine with a like 718-hour remaining to overhaul, I still came out with a better engine at a somewhat lower initial cost, a PT6 from Aerotek, Canada, than buying an IO-540 new.
Cost: As of 3/16/23, Pratt & Whitney Canada, PWC, advertises a guaranteed overhaul rate of $235,000 for an identical PT6A-21. https://www.pwc.ca/en/products-and-services/services/maintenance-programs-and-solutions/pwcsmart-maintenance-solutions/pwcsmart-pt6a/flat-rate-overhaul-program Other PWC Certified shops may charge more or less. Others offer low – mid-time engine swaps for less.
When comparing airplanes with similar times, performances, and conditions, I find myself in the rare-air 7-digit cost space. It is true whether I build or buy. No matter how I slice the numbers, I am flying a very expensive smart airplane. I would rather it be an amphibian for safety and all-composite for its super strength and ease of repair. Owning and flying a high-performance airplane I recognize is expensive. There is no getting around it. If you want a high-performance, safe airplane, you will have to pay the price of entry. When I peer into the horizon, I find no safer airplane than N71RJ, my Super Seawind. In many respects, it even outperforms several twin-engine airplanes such as climb rates, STOL, and ceilings. I have flown with other singles and twins, but for me, they just do not compare. I think you will agree; the PT6-Seawind is simply extraordinary.
ANATOMY
Let’s take an exclusive look at these PT6 series; the -20, -27, and the -34. They are all very close siblings with interchangeable parts. The attached photo displays a -27 with a nearly identical -34 which is, for all practical purposes also identical to the 27 and 34 series. Although the -20 is no longer manufactured by PWC, its siblings, or its components can be exchanged or replaced in the worldwide marketplace.
ENGINE TIMES – what they mean.
Tracking times is accomplished in any one of four ways; with paper logbooks, Engine Information Systems, EIS, and Flight Management Systems like Foreflight.
By hours flown, like 50 and 100. The manufacturer lists specific requirements at these intervals that must be accomplished. Example, a fuel filter cleaning or change.
Cycles mean the total number of take-offs and landings.
Time Since Hot Section, TSHSI is a record of when the last hot section was separated from the engine, inspected as above, and parts serviced the same as above. The PT6A-20 TSHSI is 1750 hours. 358 hours are currently logged for N71RJ with 1,392 to go.
Time Since Overhaul, TSO, means just that. When an overhaul is done the engine is cracked into its three major sections, inspected thoroughly for parts worn beyond times or tolerances, and either repaired or replaced per manufacturer standards. The current TSO for a PT6A-20 with condition monitoring is 4,000 hours. As of today, that leaves 560 remaining to overhaul. According to FAA, the average U.S. pilot flies about 50 hours per year. On average, that means 11 years. Who knows what the world will look like then? Maybe the rules will change again. When the day dawns, the owner can access PT6A-21 or later series parts and services without worrying about sibling engine incompatibility.
Weight and balance. The PT6 has a remarkable power-to-weight ratio of 550/280 or 1.96 contrasted to an IO-540 – adding 30 pounds to the base weight for accessories, we arrive at (300/468 = 0.64). That means the PT6A-20 has a remarkable 3X the P/W ratio of the Seawind standard choice piston engine. https://www.lycoming.com/engines. This translates to significantly higher numbers range, speed (200 Kts cruise), water operations, payload, passengers, class A ceilings, distance to take-off and land, electrical capacity (24 volts and 240 amps) and far less engine moving parts.
Experimental Rules, requirements, and regulations
The FAA says this: “A special airworthiness certificate in the experimental category is issued to operate an aircraft that does not have a type certificate or does not conform to its type certificate and is in a condition for safe operation. Additionally, this certificate is issued to operate a primary category kit-built aircraft that was assembled without the supervision and quality control of the production certificate holder.”
The Certification Process
The FAA’s aircraft certification processes are well established and have consistently assured safe aircraft designs. As part of any certification project, we conduct the following:
- A review of any proposed designs and the methods that will be used to show that these designs and the overall airplane comply with FAA regulations.
- Ground tests and flight tests demonstrate that the airplane operates safely.
- An evaluation of the airplane’s required maintenance and operational suitability for the introduction of the airplane into service; and
- Collaboration with other civil aviation authorities on their approval of the aircraft for import.
https://www.faa.gov/aircraft/air_cert/airworthiness_certification
REPAIRMAN CERTIFICATION is not automatically granted. FAA concluded that if you can build it you can also repair and maintain it. As required, I applied for and was granted “Repairman” certification. This permits me to perform all condition inspections and repairs from the nose to the tail for as long as I live.
PT6 MAINTENANCE, item #3, is the key requirement. N71RJ has a “Condition Inspection Program” lists every task by category and by item on an hours basis, such as 100 hours OR annually, whichever comes first. It is approved by the FAA. As long as these stated requirements are adhered to, the airplane remains compliant with its airworthiness certification. This means that component times are recommended, not mandatory. This applies equally to the engine. PWC initially recommended a 3600-hour TBO, then it revised it to 4,000 hours “on condition”. Translated, this means so long as N71RJ complies with PWC procedures and annual condition inspection procedures, it can stretch the TBO to 4,000 hours. This change is a welcome result of the experience of the PT6 community.
Lessons well learned. I protect the engine and the rest of the airplane by keeping it under a roof as much as possible. When left outside and IAW the POH, I waterproof wrap the engine and secure the propeller from windmilling. I also plug every opening a bird could enter. Moreover, I cover the canopy with a special water-tight fabric custom-made for N71RJ.
So, there you have it. You know not only what is under the hood but why – and what it means for you. Today, after 22 years of design and safety improvements, N71RJ now waits for a new owner/adventurer. Will it be you?
References. Barnstormers. Controller. TradeAplane.
Also, Read ANNUAL SURPRISES; IT’S A SAFE BET
One Response
Good going!