If modern bi-jets have such a low failure rate that ETOPS works, why are there so many single engine failures?
Posted by Recent-Day3062@reddit | flying | View on Reddit | 40 comments
I'm watching some youtube vids about accidents and emergencies hosted by real pilots (the usual ones). What I notice is there are quite a few incidents of single engine failures, especially on takeoff climb (max stress, I understand).
The idea with ETOPS is that two engines out is like a one in a billion likelihood. But single engine failures seem surprisingly common. Of course, there are lots of flights per day, and many of those planes might not even be ETOPS approved if they are domestic flights.
Guysmiley777@reddit
Selection bias. A turbine engine failure in an airliner is incredibly rare.
How many flights do you think there are per day just in the US?
Recent-Day3062@reddit (OP)
I meant the failure of a single engine in a twin turbine, not a single engine plane m
And despite people saying I watch too much YouTube, as you know by now any airliner that gets diverted for problems gets into the news. A news story about these happens maybe 1-2 times a month
Guysmiley777@reddit
How many flights do you think there are per day just in the US?
LateralThinkerer@reddit
Confirmation bias (one failure gets repeated a gazillion times on social networks) + false equivalence (piston/GA/everything else ≠ turbine 121 ETOPS)
Recent-Day3062@reddit (OP)
I meant the failure of a single engine on a twin turbine I’m not sure why everyone thought I was comparing GA to 121. Duh.
EliteEthos@reddit
You seem to be comparing piston engines with jets…
They have nothing to do with each other. Beyond the fact they both compress and ignite fuel, there are no similarities.
Recent-Day3062@reddit (OP)
No. I meant a single engine failure in a twin turbine
justcallme3nder@reddit
Big spinning thing creates thrust/power, no? /s
fireandlifeincarnate@reddit
Thrust, yes, power, not on a recip.
EliteEthos@reddit
That’s debatable on a 150
davidswelt@reddit
The next question is why nobody has found a way to make a turbine engine cheap enough (and efficient at lower altitudes) to replace the piston engines currently in use. We don't seem to have materials and processes to make cheaper blades, for example.
Recent-Day3062@reddit (OP)
As an engineer, I can never figure out what makes each turbine engine a multi-million dollar expense. Yes, there are some unusual materials, and a lot of inspection. But when you get down to it, A modern jet really has one moving part that is big. I'm talking the turbine, not lots of little parts like valves. And that moving part is axial. A piston engine is trying to blow itself apart, while a jet is just spinning.
f1racer328@reddit
It’s the certification costs that add up.
Recent-Day3062@reddit (OP)
I just read up on the metallurgy for fins. Wow.
praetor450@reddit
There is also all the research, development, and testing that happens before a new engine is put to market. That’s also part of the cost of that engine. You aren’t just paying for the material and labor to build an engine.
Just like with an airplane, the manufacturer prices it to recoup the development costs of the program.
davidswelt@reddit
Yes, but the centrifugal forces on those blades are high, all the while they experience significant heating. They need to be carefully engineered and balanced. Expensive materials and equipment. (Fun fact... there are actually little channels and holes in the blades for cooling (with fuel)..)
fireandlifeincarnate@reddit
...it's not an expense issue, it's a compression thing; a piston engine is just better at low speeds
davidswelt@reddit
A PT-6 costs what, a million US$? And the overhaul? 70k? That's the expense issue.
Maybe GA weekend warriors just need to fly faster? :)
Guysmiley777@reddit
It's the result of the concept of propulsive efficiency.
https://en.wikipedia.org/wiki/Propulsive_efficiency
TL;DR: pushing a little bit of air really fast is less efficient than pushing a lot of air less fast.
And so to be good at lower speeds you need either a really big fan like the high bypass turbofans or a propeller, which means a reduction gearbox for anything that isn't a big bore, low RPM piston engine like traditional GA engines.
Micro turbines are just too expensive for what you get in the GA world. They do make small turbine engines (like the APUs in a lot of jet aircraft), but those things are nowhere cheap enough to realistically replace the O-360s and O-540s of the world.
hawker1172@reddit
Are you comparing GA piston reliability to 121 turbine reliability?
Recent-Day3062@reddit (OP)
No. 121 turbine
f1racer328@reddit
Seriously? Does every successful flight make it onto YouTube?
Airlines have thousands of flights per day, and hundreds of airplanes flying all at once. What do you expect?
I know the failure rate at my airline, and it’s ridiculously low for how many flights we have each day.
DudeIBangedUrMom@reddit
Even if it was as common as you believe, ETOPs isn't built on the idea of both engines working; it's built on the idea of losing one and continuing safely to an alternate.
jet-setting@reddit
I think OP’s point is that ETOPS assumes the second engine will keep working, but if engine failures are so common why do we assume that second engine won’t fail as well?
So the problem is that OP assumes engine failures are common in the first place.
jet-setting@reddit
Go back and try to count the number of videos you can find. Take your time, add them all up.
There are on average 25,000+ scheduled passenger and cargo flights PER DAY in the US.
What you’re seeing is confirmation bias. You’re seeing what appears to be a trend, but in fact those failures are still incredibly rare.
BagOfMoneyNoChange@reddit
Let me get this straight...you're using youtube videos to analyze 121 engine failure statistics?
justcallme3nder@reddit
I was trying to understand what they meant by "single engine failures" because I was thinking there couldn't be any way they were comparing a single engine piston engine to a turbine engine.
Swimming_Way_7372@reddit
Sounds like it.
AdAdministrative5330@reddit
Jesus
Impossible-Bad-2291@reddit
Get the Escalade, we're outta here?
NYPuppers@reddit
Ask your local AI why jet engines fail less than turbine engines, and that is your answer.
As others said, the vast vast majority of single engine failures are piston-driven engines. Because of how these engines work, they are may more prone to failure. Whereas all business jets at this point use jet engine technology.
barcode-username@reddit
Jet engines are turbine engines, so that statement doesn't even make sense. Stop learning from AI, it's highly inaccurate for technical subjects.
Swimming_Way_7372@reddit
....."Whereas all business jets at this point use jet engine technology" nicholascageyoudontsay.jpeg
Empty-See@reddit
Just FYI, jet engines ARE “turbine engines” and both jets and turboprops produce the rotational force the same way.
Most general aviation aircraft use reciprocating engines; these have a much higher failure rate than turbines.
fireandlifeincarnate@reddit
they suggested asking "your local AI", I don't think they're the height of accurate information
usmcmech@reddit
There is a big difference between “engine failure” vs “precautionary engine shutdown”.
A high vibration on an engine might cause an engine shutdown and subsequent single engine landing. When maintenance digs into it turns out a bad sensor was the cause but risking a 20M engine destroying itself made the shutdown and diversion the correct move.
Ok_Bar4002@reddit
Why does my commuter car need to get push started so often if you never see jumper cables at a nascar starting line?
shrunkenhead041@reddit
I think OP is missing the point of how many 121 twin jet flight ops there are every day, and how rare the failures are with respect to the number of operations. Every failure is seemingly caught on camera, then hundreds of people share and comment on that one extremely rare failure.
Longjumping_Panda531@reddit
There are a lot of general aviation piston engine failures. There are NOT a lot of Part 121 turbine engine failures.
rFlyingTower@reddit
This is a copy of the original post body for posterity:
I'm watching some youtube vids about accidents and emergencies hosted by real pilots (the usual ones). What I notice is there are quite a few incidents of single engine failures, especially on takeoff climb (max stress, I understand).
The idea with ETOPS is that two engines out is like a one in a billion likelihood. But single engine failures seem surprisingly common. Of course, there are lots of flights per day, and many of those planes might not even be ETOPS approved if they are domestic flights.
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