Dead stick landing from FL270

[greg1016]

Mike Patey suffered a catastrophic engine failure on his way to Oshkosh in his PT6 powered Lancair legacy. I know youtubers aren't the most highly respected people around here, but I will admit I am a fan. Some of his early speculation sounds dubious but the one thing I will say is the guy is thorough and like when he crashed his modified Wilga Draco, he was recording and talking about it right away. Would like to hear what some of the mechs around here think. Watch it till the end.

View: https://www.youtube.com/watch?v=pgpf5ktKVBc

 

[greg1016]

ignore the dramatic thumbnail

 

[Rosstafari]

PT6's are pretty reliable. Didn't care to sit through the whole thing to find out what he suspects went wrong. Anybody able to provide a TLDR?

 

[BEEF SUPREME]

PT6's are pretty reliable. Didn't care to sit through the whole thing to find out what he suspects went wrong. Anybody able to provide a TLDR?

 

[Skåning]

youtubers

Ya had me at this

 

[greg1016]

PT6's are pretty reliable. Didn't care to sit through the whole thing to find out what he suspects went wrong. Anybody able to provide a TLDR?

I do not know the anatomy of a turbine engine or the correct terminology. He says the P2 fan failed (the last fan before the exhaust I believe). He speculates that one blade failed and caught on something stripping the rest of the fan and seizing the engine.there were also gouges in the P1 but it did not fail.

He further speculates that the underlying cause may have been from hot starting prior to his ownership/ installation, although he does fail to mention that he had sold the plane to someone else around the start of the pandemic and then bought it back, so it could have happened then.

 

[greg1016]

Additionally, the failure occurred during cruise and the engine was below TBO. All his numbers according to his engine monitor were normal up until the failure.

 

[Pilot Fighter]

With experimental aircraft, folks often do experimentalish things.

 

[greg1016]

With experimental aircraft, folks often do experimentalish things.

True but this guy is very thorough and not a cowboy

 

[trafficinsight]

True but this guy is very thorough and not a cowboy

Literally belongs to a group he calls the flying cowboys...

 

[inigo88]

While Patey has the work ethic and demeanor of a cocaine squirrel, I love the work that he does. Despite not being a formally trained engineer he’s got a great street-smart for engineering design, especially mechanism/kinematics, and his designs for the cub double-slotted leading edge slats and the Turbulence nose gear are very cool. His recent videos on the build photos for Turbulence are very impressive and show the level of structural retrofit they went through on the airframe beyond simply bolting a PT-6 to a Lancair Legacy as many others in the experimental community would do.

While I doubt I’ll change many minds, here are some key points from the video since a lot of you will write this off as experimental stuff and not sit through 40 min:

• The engine was a PT-6A-42 (850 shp, used in C208 Caravan, King Air B200, etc). From Pratt & Whitney: https://www.prattwhitney.com/en/blogs/pt6-nation/2017/07/20/interview-with-pilot-mike-patey

• This engine was the second engine. His partner had accidentally hit started engine #1, so they pulled that engine and sent it to P&W for overhaul. They bought this engine used but directly from P&W and only had 5 hours on the airplane before the failure occurred. The airplane had just come out of annual where it was worked on by an A&P specializing in turbine engines and he didn’t think that person did anything wrong.

• There was no warning in engine instrument trend data leading up to the accident. ITTs were in the mid-700s, and he pulled Garmin’s data cartridge and plotted engine data for all previous flights and saw no trends indicating a looming failure. There was a slight vibration a split-second before the failure.

• The engine failure itself was catastrophic rather than gradual. There was a loud bang which was an explosion in the power turbine section and sent bits of molten turbine into the leading edges of the wings and horizontal stabilizer, and smoke in the cockpit. He said there was a sudden stoppage of the engine during the explosion which quickly stopped the prop and blew the igniter out of the bottom of the combustion chamber.

• He borescoped the engine near the end of the video and shows that the power turbine PT2 disc is nearly gone, while the PT1 disc behind it is totally intact. Since air flows backwards towards the nose in a PT6 I believe PT2 is the last turbine the exhaust hits before exiting the engine. So what causes the last power turbine in the engine to spontaneously explode if temperatures were all operated within normal limits? Potentially material science metallurgy issues with the original billet the turbine was machined from, resulting in lower than published material allowables, or flaws and inclusions resulting in early fatigue crack propagation starters and lower than expected fatigue life (see titanium fan blade failure in southwest 737 that killed the passenger sitting behind the wing for another example of this). Patey thinks that a King Air pilot hot-started the engine one or more times and never reported it in its previous life on a B200, because the logs were clean. This seems like as reasonable a hypothesis as any to me especially given the recent corporate aviation anecdotes on this board.

• They’re sending the engine back to Pratt, who is going to do a tear down and forensic analysis - so this probably isn’t going to be chalked up to “dumb experimental guys effed it up.” But if it is, I’m glad they’re committed to getting to the bottom of it rather than sweeping it under the rug.

I believe PT2 is the furthest left power turbine. You guys who work on and fly them correct me if I’m wrong.

 

[Roger Roger]

I don’t know about the -42 but some flavors of the PT6 did have issues with the CT blades deciding to take the day off in a very exciting manner, supposedly the fix was the new latest greatest single-crystal CT blades. But if I’m reading right this was a PT. One of the caravan crashes about 10+ years back was caused by improper blasting media usage on a turbine wheel, I think that got a repair station in trouble

 

[inigo88]

Here are a couple of stills from the video. I think it was taken with the “poor man’s borescope” (iPhone stuck in the exhaust duct looking aft). The PT2 disc exploded. The PT1 blades are damaged but I agree with Patey that it looks like damage inflicted on PT1 by the catastrophic failure of PT2.

Edit: Here’s what the power turbines look like new. Really impressive mechanical assemblies!

Source: Power Section Repairs - Southeast Turbines, Corp:

 

[greg1016]

Here are a couple of stills from the video. I think it was taken with the “poor man’s borescope” (iPhone stuck in the exhaust duct looking aft). The PT2 disc exploded. The PT1 blades are damaged but I agree with Patey that it looks like damage inflicted on PT1 by the catastrophic failure of PT2.

View attachment 72852

View attachment 72853

Thanks for the thorough synopsis. Saw the video last night just before bed and just getting back to the forum after work. Much more thorough than I'd have done. Patey isn't your average aviation youtuber and if anything his channel is more engineering/experimentalist than aviation. He was breaking records before he was on youtube.

Although he is rich he isn't branson/faucett rich and he builds his own stuff instead of partnering with others. Steve Faucett died in a Super D didn't he? You don't need an experimental to kill yourself. In fact the majority of fatal experimental crashes are the result of pilot error, same as GA. I really got into Patey's channel when he was building that modified carbon cub because when he actually stress tested his spar design before he installed it. If anything he errs on the side of overbuilding.

 

[killbilly]

I didn’t know he had bought the airplane back.

The guy he sold it to used to fly it out of JYO and I used to see him on the ramp sometimes. One day while with a student I approached him and asked him if we could take a close-up look at the airplane.

It really is an incredibly well-built machine, and I didn’t have enough time to ask him about details on what structural improvements might have been made with adding that power plant to such a light airplane but I hope they were significant.

 

[greg1016]

I didn’t know he had bought the airplane back.

The guy he sold it to used to fly it out of JYO and I used to see him on the ramp sometimes. One day while with a student I approached him and asked him if we could take a close-up look at the airplane.

It really is an incredibly well-built machine, and I didn’t have enough time to ask him about details on what structural improvements might have been made with adding that power plant to such a light airplane but I hope they were significant.

He is releasing a series using old stock video from the original build right now. I'd have to go back and watch to tell you the specifics, but it not only involved reinforcement, but also a major increase in fuel capacity (something like 3x the norm for a lancair). It's cool you saw it in person.

 

[killbilly]

He is releasing a series using old stock video from the original build right now. I'd have to go back and watch to tell you the specifics, but it not only involved reinforcement, but also a major increase in fuel capacity (something like 3x the norm for a lancair). It's cool you saw it in person.

I figure he had to do a bunch of reinforcement work on the airframe - just because you put a big-ass motor on the airplane doesn't mean that Vne automatically goes up.

Not having an aero engineering background, I do wonder what mods have to be done in that case. I'm guessing significant work on the elevator and stabilizer assemblies.... @inigo88 - can you shed a little light on that?

 

[greg1016]

I figure he had to do a bunch of reinforcement work on the airframe - just because you put a big-ass motor on the airplane doesn't mean that Vne automatically goes up.

Not having an aero engineering background, I do wonder what mods have to be done in that case. I'm guessing significant work on the elevator and stabilizer assemblies.... @inigo88 - can you shed a little light on that?

Watch his last couple videos, he gets into it, I'm sure he isn't finished yet.

 

[Pilot Fighter]

Regardless of the smarts and skill at play, a one of one is a prototype and its pilot is a test pilot.


That said, I’m glad that a few folks are doing interesting things in the experimental-amateur built category.

 

[killbilly]

Regardless of the smarts and skill at play, a one of one is a prototype and its pilot is a test pilot.


That said, I’m glad that a few folks are doing interesting things in the experimental-amateur built category.

Along those lines....I'm not able to look it up right now, but SUPPOSEDLY there's an Australian firm who has developed a 200-hp turboprop engine for the EAB market. That would be an amazing game changer, especially if the costs were at or below current recip prices. Last I read they were going to debut the prototype at Oshkosh this year.