Redsand187
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How often does an engine come off?

Fri Jun 28, 2019 8:55 pm

I am working on a project and I need a rough estimate of how often an engine is removed from the wing of a widebody jet.

My only experience anywhere near this is tour Alaska's maintenance facility, where if I remember correctly, they had 7 CFFM56's from their 737's in the engine shop and that they were on a constant rotation as they preferred to do full swaps vs on-wing maintenance. A little math, and that brings me to an estimate that they are pulling an engine off a plane on average once per year!?!?

Is that anywhere near accurate? And how does that compare to widebody jets? It sounded like ingestion was a common reason the engines come off. I would assume widebodies would be much less often due to less cycles.

If I bought a new A350 and operated daily, how many times would be reasonable to expect that an engine has to come off?
 
strfyr51
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Re: How often does an engine come off?

Fri Jun 28, 2019 11:51 pm

are they removing the engines for Performance or Time? At United our engines are "On Condition" That as long as takeoff performance is good ? We can continue to fly the engine. you might have to define your question
 
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fr8mech
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Re: How often does an engine come off?

Sat Jun 29, 2019 1:11 am

I'll go on a limb and say almost all operators of wide-body aircraft change engines "on-condition". The engines are monitored for performance, and the engine is changed when it has deteriorated to unacceptable levels.

Of course, FOD damage will cause an engine to be pulled prematurely.
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ltbewr
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Re: How often does an engine come off?

Sat Jun 29, 2019 12:20 pm

I would suspect that the oil from an oil change is tested to see if contaminants, if signs of worn metal in it. If there is beyond a certain limit of such contaminants or worn metal, then the engine would be have to be removed to be examined further and fixed. .
 
slcguy
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Re: How often does an engine come off?

Sat Jun 29, 2019 1:35 pm

As stated in most cases it is on-condition or damage (FOD / bird strike etc). In some cases it may be also be accessary equipment (hydraulic/ electrical/ pneumatic). If the problem may take time to repair (difficulty in troubleshooting the problem or parts availability etc) they may swap out the engine to get the aircraft back in the air where it can make money.
 
Dalmd88
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Re: How often does an engine come off?

Sat Jun 29, 2019 4:03 pm

ltbewr wrote:
I would suspect that the oil from an oil change is tested to see if contaminants, if signs of worn metal in it. If there is beyond a certain limit of such contaminants or worn metal, then the engine would be have to be removed to be examined further and fixed. .

Oil in Jet engines never gets changed. We just continuously top off to full. When the filters get changed they get a quick inspection for metal particles. Some airlines do a oil sample program where the oil is inspected by chemical make up for problems. Chip detectors are regularly checked for metal particles and results are lab test to see if something is coming apart in the oil system.

Other than that the performance is tracked Most newer planes report automatically through ACARS snapshots of the output which is watched. Also internal Boroscope inspections are performed to check the condition of the internal blades and burner areas.

As for how long they last on wing, it varies greatly by engine program. Part of it comes down to what you do when you pull an engine for repair. How much do you change when it's apart? How much do you want to spend? How much you spend really relates to how many hours you get.
 
diverted
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Re: How often does an engine come off?

Sat Jun 29, 2019 4:59 pm

Here's some interesting info from CFM regarding CFM56's


3C engine holds the all-time world record for initial time on wing. In September 2003, the engine was removed after reaching 40,728 hours and 17,504 cycles without a single shop visit, surpassing the previous record of 40,531 hours set in 2000.


HANOVER, Germany - German airline TUIfly and CFM International today celebrated a new first-run time-on-wing world record set by a CFM56-7B engine powering one of the airlines Boeing Next-Generation 737-800 aircraft. The engine logged more than 50,000 hours without a shop visit.
The CFM56-7B engine was recently removed for LLP (life-limited part) replacement. Up until its removal, the engine was performing flawlessly and show very good EGT (exhaust gas temperature) margin. EGT margin is the primary indictor of an engine's fuel efficiency.
TUIfly was able to keep the engine on wing through continuous diagnostics, which enabled the maintenance team to optimize the maintenance intervals for the engine. In addition, the airline implemented fuel-efficient, noise-optimized cockpit procedures, along with periodic engine washes, which extended the life of the engines and helped to reduce fuel consumption.
 
Redsand187
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Re: How often does an engine come off?

Mon Jul 01, 2019 3:31 pm

fr8mech wrote:
I'll go on a limb and say almost all operators of wide-body aircraft change engines "on-condition". The engines are monitored for performance, and the engine is changed when it has deteriorated to unacceptable levels.

Of course, FOD damage will cause an engine to be pulled prematurely.

I understand that probably all of these are on-condition for overhaul. I am wondering how common FOD is and any other reason for removing an engine as well as typical on-condition time on wing.

Like I said, when I was at Alaska's hanger I was surprised how many engines they had and how often it sounded like they were removing and replacing engines for various reasons almost none for regularly scheduled overhaul.

From what I read, a CFM56 should be able to stay on a wing for nearly 10 years, but at Alaska, it appeared it was happening way more often than that. It wasn't the focus of my visit so I really didn't think a year later that I'd have this question, and even then it's not completely relevant to what I am wanting to know. It goes to reason, that if my observation was accurate a widebody's engines may come off more often/sooner than expected.
 
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zeke
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Re: How often does an engine come off?

Mon Jul 01, 2019 5:40 pm

Redsand187 wrote:
If I bought a new A350 and operated daily, how many times would be reasonable to expect that an engine has to come off?


In theory never.

The Trent XWB produces an enormous amount of data (as does the aircraft), if any parameter is trending the wrong way the engine will be removed. The engine configuration is also not a stationary target, service bulletins are available to improve engine performance which operators may elect to incorporate.

That is possibly what you are seeing on the CFM56, some improvement package being embodied.
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fr8mech
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Re: How often does an engine come off?

Mon Jul 01, 2019 8:54 pm

Redsand187 wrote:
fr8mech wrote:
I understand that probably all of these are on-condition for overhaul. I am wondering how common FOD is and any other reason for removing an engine as well as typical on-condition time on wing.


You can’t predict a FOD event, so you can’t really forecast it, but I’m sure our powerplant engineering group has a “budget” for non-ECM (engine condition monitoring) engine changes.

I remember we pulled half-a-dozen engines for FOD in a 3 or 4 month span one year. I’m not sure that we’ve pulled one yet this year for FOD.

As for on-wing time, I’ll see if I can survey some data when I get to work tomorrow night. But, I can assure, we don’t come anywhere near changing an engine on each aircraft every year. I suspect 5 or 6 years between engine changes, probably more.
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n901wa
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Re: How often does an engine come off?

Tue Jul 02, 2019 5:56 am

We also change engines for life limited parts. As engs get better and stay on wing longer some parts in the engine are Life limited. I am changing a Pratt 4000 for life limited parts in a few days. It will go back to the shop, and will replace anything on watch or show any issues and replace the LLP and rebuilt and made serviceable.

I do routine Boroscopes and we check internal conditions, and usually reinspect around 500 cycles on the high side and if we find issues will reduce the cycles and work with engineering or thru the manuals of any damage we find inside the engines. We had a reinspect on a issue every 56 Cycles for at least 2 years before we removed the eng for another issue.

Like fr9mech above the eng usually stays on wing 5 or 6 years, and I think we had a RB211-524 on wing for 10 years. Was the longest eng to stay on wing, but I bet that someone has passed that by now. I know some Trents that have been on wing at least 8 years.

HTH :)
 
Armadillo1
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Re: How often does an engine come off?

Tue Jul 02, 2019 2:51 pm

n901wa wrote:
I do routine Boroscopes and we check internal conditions, and usually reinspect around 500 cycles on the high side and if we find issues will reduce the cycles and work with engineering or thru the manuals of any damage we find inside the engines. We had a reinspect on a issue every 56 Cycles for at least 2 years before we removed the eng for another issue.


so for short haul it means ~3 month for reinspect and about every 2 week in 2 years if found issue?
 
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fr8mech
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Re: How often does an engine come off?

Wed Jul 03, 2019 1:18 am

I just looked at our PW4158 engines. Our highest time engine (since installation) has been on-wing for 9383 hours and 5973 cycles. It was installed on 9/2010. More than half the installed engines have more than 5000 hours since last removal.

We borescope the hot section of the 4158 every 2000 hours or 600 cycles, whichever comes first. There would be reduced intervals for damage/wear found during the routine inspections.
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.
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n901wa
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Re: How often does an engine come off?

Wed Jul 03, 2019 4:49 am

Hi Armadillo1, It all depends on what type of eng and what type of Boroscope is done. But yes if you flew 5 or 6 cycles ( we don't see any Aircraft that pull that many a day in our station, but in other fleets types in other stations they do) a day your looking at 3 months to perform a Hot section ( Combustion Chamber Boro) Planning usually tries to get it to a Inspection Station at around 20 Cycles remaining.
As for lowered Inspection Intervals, it can run from normal all the way down to what ever the Engineer is comfortable with. We had one that was reduced to 23 cycles to make sure nothing was growing and after a baseline was set after a few boroscopes that showed it was not growing, it was extended to 56 cycles.
I forgot the watch cycles but we had one where we reinspected it every week. It made it hard to route it back to us every week.
HTH :-)
 
StTim
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Re: How often does an engine come off?

Wed Jul 03, 2019 7:19 am

A slightly different aspect of this.

I have heard that airlines sensibly try to have engines at different stages of life on a frame - such that if an life related issue appears it is unlikely to impact both engines.

On an long time production frame does that mean an engine swap almost immediately after the delivery flight?

On a new program (such as say BA taking it’s first XWB -1000, thus also new engine to the IAG group) how do they organise engines in order to achieve the same situation?
 
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fr8mech
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Re: How often does an engine come off?

Wed Jul 03, 2019 8:55 am

StTim wrote:
A slightly different aspect of this.

I have heard that airlines sensibly try to have engines at different stages of life on a frame - such that if an life related issue appears it is unlikely to impact both engines.

On an long time production frame does that mean an engine swap almost immediately after the delivery flight?

On a new program (such as say BA taking it’s first XWB -1000, thus also new engine to the IAG group) how do they organise engines in order to achieve the same situation?


I know we've never done that when bringing new aircraft online. The only thing we do with a new type is a practice engine change after the aircraft has been in service a few months.
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.
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Dalmd88
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Re: How often does an engine come off?

Wed Jul 03, 2019 3:23 pm

StTim wrote:
A slightly different aspect of this.

I have heard that airlines sensibly try to have engines at different stages of life on a frame - such that if an life related issue appears it is unlikely to impact both engines.

On an long time production frame does that mean an engine swap almost immediately after the delivery flight?

On a new program (such as say BA taking it’s first XWB -1000, thus also new engine to the IAG group) how do they organise engines in order to achieve the same situation?

Yes, we do 'stagger changes' all the time. It would not be done on delivery of the first airframe. all the engines in the airline's inventory would be zero time. After some time in service a spare would be swapped out and then the the removed engine would get put on a new aircraft and that removed engine gets put on another older airframe. I don't think we have done this with the A350 fleet at DL yet. That has been in service for about a year now so I don't know when or even if the stagger will happen. I've seen it quite a bit on the narrow body fleets at DL.
 
Redsand187
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Re: How often does an engine come off?

Wed Jul 03, 2019 6:41 pm

fr8mech wrote:

As for on-wing time, I’ll see if I can survey some data when I get to work tomorrow night. But, I can assure, we don’t come anywhere near changing an engine on each aircraft every year. I suspect 5 or 6 years between engine changes, probably more.


This is more along the line of what I expected 5-6 years sounds a lot more reasonable. Thanks!
 
Redsand187
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Re: How often does an engine come off?

Wed Jul 03, 2019 6:41 pm

fr8mech wrote:

As for on-wing time, I’ll see if I can survey some data when I get to work tomorrow night. But, I can assure, we don’t come anywhere near changing an engine on each aircraft every year. I suspect 5 or 6 years between engine changes, probably more.


This is more along the line of what I expected 5-6 years sounds a lot more reasonable. Thanks!
 
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AirlineCritic
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Re: How often does an engine come off?

Wed Jul 03, 2019 6:50 pm

Those are some surprisingly long hours for a complex mechanical system to stay on a wing, without major maintenance! Kudos for the industry to be able to achieve such high reliability and durability.

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