Category Archives: PT6A

How To Recognize, Resolve and Prevent Propeller Lock-Up

This article originally appeared on the P&WC Airtime Blog.

If you’re flying a PT6A-powered aircraft and the propeller has unexpectedly locked into place, don’t panic: there’s most likely a simple explanation and an easy solution. Our expert explains all.

WHAT IS PROPELLER LOCK-UP?

Before starting a turboprop engine, it is common practice for ground personnel to manually turn the aircraft’s propeller to make sure it’s rotating freely with no abnormal noises. When moved slowly, the propeller will usually turn with ease.

But not always. Sometimes it doesn’t turn at all, or it rotates while making a scraping noise.

Most likely, this indicates a thermal lock-up, says  Stéphan Michon, senior technical specialist at Customer First Centre, the response centre that operates around the clock to support customers worldwide.Propeller lock-up is a known, easily resolved phenomenon that occasionally occurs with PT6A and some other engines, as a natural consequence of how these turboprop engines are designed. Stéphan Michon, senior technical specialist, Customer First Centre

There’s no sure-fire method of preventing propeller lock-up, although there are steps you can take to reduce the probability of it occurring, as discussed below.

The good news is that it can be handled with the cheapest, simplest solution of them all: doing nothing.

WHY LOCK-UP HAPPENS

Regardless of the aircraft’s mission type, propeller lock-up is most likely to occur when landing in a cold environment, where the outside air temperature (OAT) is low.

Fundamentally, it is caused by the temperature differential between the engine’s external casing and the inner components.

“When the engine is shut down, the cooling rate of the various components varies,” notes Stéphan. “Since the outside case is typically a relatively thin sheet of metal that’s exposed to the cooler nacelle temperature, its cooling rate is quite fast. On the other hand, the power turbine disks in the hotter engine interior have a slower cooling rate.”

The differing rates of thermal contraction combined with the extremely small tolerances within the engine sometimes causes temporary propeller lock-up.

WHEN LOCK-UP HAPPENS

The window of opportunity for thermal lock-up to occur is quite short, as Stéphan explains.At some point, when the outside case has returned to its ‘cold’ state, but the disk assembly is still warm, the power turbine disk and blades’ outside diameter will still be slightly enlarged due to slower thermal contraction and will touch the shroud’s inside diameter when rotated. They may lock into place as a result of friction, causing propeller lock-up. Stéphan Michon, senior technical specialist, Customer First Centre

In other words, lock-up only happens during the relatively brief period when the engine’s internal components are still cooling down after the engine has been turned off.

As Stéphan is quick to point out, propeller lock-up does not mean there is something wrong with your engine. He compares it to the wipers on a car freezing to the windshield – something that happens occasionally in specific circumstances, but does not signal any underlying issues.

“Over time, propeller lock-up becomes less likely because normal wear on the turbine blades will slightly increase the tip clearances,” adds Stéphan. “It’s therefore slightly more frequent with brand-new engines or engines that have just been overhauled or refurbished, when the clearances are at their smallest.”

HOW TO DEAL WITH LOCK-UP

Propeller lock-up will resolve itself once the engine interior and exterior temperatures have somewhat equalized. That means all you need to do is wait for it to finish cooling down, with no corrective action required.

How long does this take? It varies depending on the aircraft, the engine model, OAT and other factors. There’s no way to put an exact number on it, says Stéphan, but it typically takes around five to 25 minutes for the engine interior to cool sufficiently.

If you don’t realize that the propeller has locked, you can still safely start the PT6A engine. Once it starts, the outside case will warm up quickly, eliminating the temperature differential and releasing the propeller lock-up. 

While thermal lock-up is more likely to occur when landing in a cold environment, it will also be resolved more quickly, since the engine internals will cool down more quickly compared to a warmer environment. Conversely, in a warmer environment, there may be a longer delay before lock-up occurs after shutdown, and the propeller may remain locked somewhat longer as well.

Stéphan suggests a couple of tips for proactively reducing the likelihood of propeller lock-up when landing in a cold environment:You can idle the engine for slightly longer – say 30 seconds to one minute – before you shut down the engine. You can also do one or two dry motoring cycles immediately after the shutdown, meaning that you turn the engine with the starter (within its limitations) while keeping the fuel and ignition off, which will draw cool air inside. Stéphan Michon, senior technical specialist, Customer First Centre

Both of these steps will help to cool the power turbines, making it less likely that thermal lock-up will occur due to a temperature differential.

If the situation is not resolved as described above, or if you have any doubts, consult the relevant section of the engine maintenance manual or contact Pratt & Whitney’s Customer First Centre for assistance.

Read more practical advice for PT6A operators in our Airtime blog, and download our Know My PT6 app from the App Store and Google Play.

Inside the Wasp Shop with the Aeroshell Aerobatic Team & Covington Aircraft

Gene McNeely started flying airshows in 1986 and has been a stalwart presence on the AeroShell aerobatic team, flying a Wasp-powered North American T-6. He can only guess at his total flying time behind the engine: “I would say 15,000 hours…probably more than that.” He does remember exactly how he got there, though. “I got out of the Navy and…started cropdusting, and the first engine I sat behind was the [Pratt &Whitney] R-985, which we’d adapted to the Stearman,” he recalls.

Continue reading Inside the Wasp Shop with the Aeroshell Aerobatic Team & Covington Aircraft

The TBM 700 Powered by the PT6A-64 Led to Even Faster TBM Variants

The SOCATA TBM (now Daher TBM) is a family of high-performance single-engine turboprop light business and utility aircraft manufactured by Daher. It was originally collaboratively developed between the American Mooney Airplane Company and French light aircraft manufacturer SOCATA.

The design of the TBM family originates from the Mooney 301, a comparatively low-powered and smaller prototype Mooney developed in the early 1980s. Following Mooney’s acquisition by French owners, Mooney and SOCATA held a series of in-depth discussions on the potential for co-developing a new enlarged turboprop design derived from the earlier 301; these resulted in the formation of a joint venture for the purpose of developing and manufacturing the envisioned aircraft, which was designated as the TBM 700. From the onset, the emphasis was placed upon the design’s speed, altitude, and reliability. Upon its entry into the market in 1990, it held the distinction of being the first high-performance single-engine passenger/cargo aircraft to enter production.[

Shortly after launch, the TBM 700 was a market success, which quickly led to the production of multiple variants and improved models, often incorporating more powerful engines and new avionics, amongst other features. 

The prefix of the designation, TBM, originated from the initials “TB”, which stands for Tarbes, the French city in which SOCATA is located, while the “M” stands for Mooney. At the time of its conception, while several aviation companies had studied or been otherwise considering the development of such an aircraft, the envisioned TBM 700 was the first high-performance single-engine passenger/cargo aircraft to enter production. From the onset, key performance criteria were established for the design, demanding a high level of reliability while also being capable of an unequaled speed/altitude combination amongst the TBM 700 other single-engined peers.

The Pratt & Whitney CanadaPT6A-64 engine, providing up to 700 shp (522 kW) powers the TBM 700. According to Flying Magazine, the PT6A-64 engine is “the secret to the TBM 700’s performance. At sea level, the engine is capable of generating a maximum 1,583 shp (1,180 kW), which is intentionally limited to 700 shp (522 kW) on early TBM models; the limit allows the aircraft to maintain 700 shp (522 kW) up to 25,000 ft (7,620 m) on a typical day. Engine reliability and expected lifespan are also enhanced by the limitation. While the typical engine overhaul life is set as 3,000 flight hours between overhauls, on-condition servicing can also be performed due to various engine parameters being automatically recorded by the engine trend monitoring (ETM) system. Data from the ETM can be reviewed by the engine manufacturer to determine the level of wear and therefore the need for inspection or overhaul. The ETM, which is connected to the aircraft’s air data computer, also provides information to enable easy power management by the pilot.

The Douglas DC-3: 85 Years and Going Strong

The Douglas DC-3 Doesn’t Know the Meaning of the Word “Quit”

The same year the German airship Hindenburg crossed the Atlantic, the still-flying-today Douglas DC-3 was introduced to the world. The DC-3 is widely viewed as one of the most significant transport aircraft in history, due to its massive and long-lasting impact on the airline industry, and aerospace engineering. I got the chance to interview Ric Hallquist, the retired Chief DC-3 Pilot for Missionary Flights International who flew and worked on the beefy twin engine transport plane for over 30 years.

Continue reading The Douglas DC-3: 85 Years and Going Strong

Piper wins European certification for Autoland system on M600/SLS

Piper Aircraft has gained European approval for its M600/SLS equipped with the Garmin Autoland-based Halo safety system.

Delivery of the initial Halo-equipped aircraft to a European customer will take place late in the second quarter, says the Vero Beach, Florida-based airframer.

Continue reading Piper wins European certification for Autoland system on M600/SLS

A Longer Look at the PT6A-34 Powered Viking 400

An airplane that can go virtually anywhere, do anything, and operate in the most extreme weather—and that could sell for twice what you paid for it after 30 years—might sound like a fantasy. But the iconic DHC-6 Twin Otter, which de Havilland Canada ­produced, fits that description. It helped launch the commuter and regional airline industry in North America, remains the backbone of maritime coastal patrols for many navies, and serves the mining and oil industries worldwide. It lands on wheels, big tundra tires, straight floats, amphibious floats, and skis. Runways are optional. Nice flat surfaces of any kind are kid stuff. When it’s 60 below in Antarctica and some scientist needs to be medevaced, this is the airplane they send.

Continue reading A Longer Look at the PT6A-34 Powered Viking 400