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WesternDC6B
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Joined: Thu Mar 14, 2013 3:05 pm

Engine wear: What happens?

Sun Feb 09, 2020 1:33 pm

Something I have pondered for some time. What actually happens as a jet engine stacks up hours, and then someone decides it’s time to take it off the wing and give it a rebuild? I use the term jet engine genrically, be it relatively low bypass or high.

In a reciprocating engine, there are factors like wearing out piston rings, cylinder walls becoming a bit ovoid, bearing wear, valves needing attention.

What goes weak or bad in a jet? I am not speaking of excess bearing wear due to desert use, or the combustion cans (?) cooking out due to many full throttle uses. I mean just everyday hours as they stack up.
A big heart is commendable. An enlarged heart is a medical condition.
 
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WesternDC6B
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Posts: 492
Joined: Thu Mar 14, 2013 3:05 pm

Re: Engine wear: What happens?

Sun Feb 09, 2020 1:37 pm

WesternDC6B wrote:
Something I have pondered for some time. What actually happens as a jet engine stacks up hours, and then someone determines it’s time to take it off the wing and give it a rebuild? I use the term jet engine genrically, be it relatively low bypass or high.

In a reciprocating engine, there are factors like wearing out piston rings, cylinder walls becoming a bit ovoid, bearing wear, valves needing attention. Turboprops, there are reduction gear issues and also the devices for adjusting prop pitch.

What goes weak or bad in a jet? I am not speaking of excess bearing wear due to desert use, or the combustion cans (?) cooking out due to many full throttle uses. I mean just everyday hours as they stack up.
A big heart is commendable. An enlarged heart is a medical condition.
 
CosmicCruiser
Posts: 2389
Joined: Tue Feb 22, 2005 3:01 am

Re: Engine wear: What happens?

Sun Feb 09, 2020 3:00 pm

Looks to me like you answered the question. I don't think bearing wear is limited to "desert use". I was flying a 727 once and got a thrust reverser unlocked alert. We shut the engine down and landed at our destination. The next day maint told me it was a worn switch that caused the"false alert". I learned the jet made one more leg with another shutdown. The engine was changed due to worn bearing. ( I wasn't in the desert either.)
 
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747classic
Posts: 2809
Joined: Sat Aug 15, 2009 9:13 am

Re: Engine wear: What happens?

Sun Feb 09, 2020 3:55 pm

Engine removal causes can be assigned into four general categories consisting of:
1.) EGT Margin (EGTM) Erosion;
2.) Expiry of Life Limited Parts (LLPs);
3.) Hardware Deterioration,
4.) Other Unscheduled Removal Causes.

For detailed info, see : http://www.aircraftmonitor.com/uploads/ ... ers_v1.pdf
And select chapter 3 : Turbofan maintenance concepts.
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
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fr8mech
Posts: 7884
Joined: Mon Sep 26, 2005 9:00 am

Re: Engine wear: What happens?

Sun Feb 09, 2020 4:26 pm

Cracks in the combustors.
Deterioration of turbine blade/vane coatings.
Cracks and/or missing material in the turbine section.
Air seal breakdown in the bearing cavities.
Bearing wear resulting in increased vibration.
Or, vibration resulting in increased bearing wear.

Of course, there is always FOD that can directly result in an engine change, or lead to premature wear, resulting in decreased margins.
When seconds count...the police are minutes away.
Unless it's expressly prohibited, it's allowed.
You are not entitled to a public safe space.
Ego Bibere Capulus, Ut Aliis Sit Vivere
 
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WesternDC6B
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Joined: Thu Mar 14, 2013 3:05 pm

Re: Engine wear: What happens?

Mon Feb 10, 2020 12:14 pm

Thanks to you all!
A big heart is commendable. An enlarged heart is a medical condition.
 
gregorygoodwin
Posts: 60
Joined: Wed Jun 11, 2014 10:01 pm

Re: Engine wear: What happens?

Mon Feb 10, 2020 6:36 pm

On our aircraft the usual cause of engine removal is hot section turbine blade wear or case defects, these components live a hard life. This is usually on our GE CF6-6 engines. As far as I know, we (FDX) are the only ones still operating this variant. They have probably been overhauled numerous times. They will fail the boroscope inspection more than any other.

Gregory
P.S. The MD10's will be gone soon,probably by May 2020.
 
strfyr51
Posts: 4293
Joined: Tue Apr 10, 2012 5:04 pm

Re: Engine wear: What happens?

Mon Feb 10, 2020 8:28 pm

[quote="WesternDC6B"]Something I have pondered for some time. What actually happens as a jet engine stacks up hours, and then someone decides it’s time to take it off the wing and give it a rebuild? I use the term jet engine genrically, be it relatively low bypass or high.

In a reciprocating engine, there are factors like wearing out piston rings, cylinder walls becoming a bit ovoid, bearing wear, valves needing attention.

What goes weak or bad in a jet? I am not speaking of excess bearing wear due to desert use, or the combustion cans (?) cooking out due to many full throttle uses. I mean just everyday hours as they stack up.[/fan F
clearance of the Fan, compressor , diffuser, Turbine cases, erosion wear of the compressor blades, Turbine blades and Fan blades accessory Drive shaft wear including seals, Bearing seals and Drive seals for the accessories like the fuel pump, oil Pump, Sometimes wiring to the Electronic Control units if not the Units themselves, all the engine Bearing housings and the bearings
Not much is not touched in a jet engine overhaul. and all of it can be repaired and refurbished. including Compressor and Turbine Blades and Rotors. You would be amazed at what a good machine shop can do. I used to come into work sometimes on my day off Just to tour the Engine Overhaul Facility at United's Engine Overhaul Facility at SFO. It was always an education.
I saw many things from another perspective as I worked Line Maintenance. I saw and talked to guys who Knew more than I did about engines and they gave me tips and pointers because not everything can be learned in class or from a book. once I even got to assist in an on wing turbine change that I asked for as we didn't have a spare engine coming out of the shop for a couple of days and I needed an engine Now. The VP of maintenance congratulated me before he told me[b] to NOT do it again.[/b] I really wanted to see if we could do it at all as I'd done over the wing turbine changes on Lockheed Electra's, Convair 580's and P-3C's while in the Navy. Which was where I got the Idea. I'd worked with some guys who had done Long shaft changes on wing while they were working at TWA and they and the guys from the turbine shop were all ready to indulge me. the only problem? I took a turbine assembly that was for an overhauled engine and messed up their delivery schedule as they had to wait for the turbine I removed to be Overhauled to make up the loss which never occurred to me to think of..
that airplane flew another 34000 hours and they didn't have to remove that engine, It was on wing for close to 50,000 hours, I heard that record was beat later.
 
Max Q
Posts: 7998
Joined: Wed May 09, 2001 12:40 pm

Re: Engine wear: What happens?

Mon Feb 10, 2020 11:32 pm

strfyr51 wrote:
WesternDC6B wrote:
Something I have pondered for some time. What actually happens as a jet engine stacks up hours, and then someone decides it’s time to take it off the wing and give it a rebuild? I use the term jet engine genrically, be it relatively low bypass or high.

In a reciprocating engine, there are factors like wearing out piston rings, cylinder walls becoming a bit ovoid, bearing wear, valves needing attention.

What goes weak or bad in a jet? I am not speaking of excess bearing wear due to desert use, or the combustion cans (?) cooking out due to many full throttle uses. I mean just everyday hours as they stack up.[/fan F
clearance of the Fan, compressor , diffuser, Turbine cases, erosion wear of the compressor blades, Turbine blades and Fan blades accessory Drive shaft wear including seals, Bearing seals and Drive seals for the accessories like the fuel pump, oil Pump, Sometimes wiring to the Electronic Control units if not the Units themselves, all the engine Bearing housings and the bearings
Not much is not touched in a jet engine overhaul. and all of it can be repaired and refurbished. including Compressor and Turbine Blades and Rotors. You would be amazed at what a good machine shop can do. I used to come into work sometimes on my day off Just to tour the Engine Overhaul Facility at United's Engine Overhaul Facility at SFO. It was always an education.
I saw many things from another perspective as I worked Line Maintenance. I saw and talked to guys who Knew more than I did about engines and they gave me tips and pointers because not everything can be learned in class or from a book. once I even got to assist in an on wing turbine change that I asked for as we didn't have a spare engine coming out of the shop for a couple of days and I needed an engine Now. The VP of maintenance congratulated me before he told me to NOT do it again. I really wanted to see if we could do it at all as I'd done over the wing turbine changes on Lockheed Electra's, Convair 580's and P-3C's while in the Navy. Which was where I got the Idea. I'd worked with some guys who had done Long shaft changes on wing while they were working at TWA and they and the guys from the turbine shop were all ready to indulge me. the only problem? I took a turbine assembly that was for an overhauled engine and messed up their delivery schedule as they had to wait for the turbine I removed to be Overhauled to make up the loss which never occurred to me to think of..
that airplane flew another 34000 hours and they didn't have to remove that engine, It was on wing for close to 50,000 hours, I heard that record was beat later.




Fascinating, I really enjoy your posts and always learn something new
The best contribution to safety is a competent Pilot.


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