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TriL1011Star
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Why are engines on planes changed so often?

Sun Mar 14, 2021 8:15 pm

So many times you will hear of an aircraft who is operating with leased engines, or have had multiple engine changes. Why is this? It doesn't seem like a plane is very old when engines start getting swapped out either.
 
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Starlionblue
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Re: Why are engines on planes changed so often?

Tue Mar 16, 2021 4:06 am

Engines (and aircraft, and APUs) are leased in order for the operator to have a reliable and even expenditure over time. If you own the engines outright and one breaks down in dramatic fashion, you have an unpredictable and large expense. If you lease the engine you keep paying the same amountand the lessor swaps it out.

How often is often? ;)

Engines might get swapped out because they need to go into maintenance and the operator can keep the aircraft flying with other engines. They're also probably the parts that are under the most stress, so it would make sense that they be given some TLC with reasonable frequency.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
gloom
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Re: Why are engines on planes changed so often?

Tue Mar 16, 2021 6:36 am

Do lessors also swap engines based on time on wing? I do know owners do that to their own engines to avoid both: maintenance check on significant number of engines at one time, and balance wear&tear between different planes flying different routes. Aaaah, and they also match engines closing to maintenance to the ones just back from maintenance, to reduce risks. However, for a lessor this would imply more engine movements than on owner side (who usually does all of this only in one airport/engine shop), so is it also reasonable, or not?

Cheers,
Adam
 
Flow2706
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Re: Why are engines on planes changed so often?

Tue Mar 16, 2021 2:33 pm

Some airlines also choose to „de-pair“ engines on new aircraft (i.e. swap on of the engines on a new aircraft with the engine of an older aircraft) if there is a reliability issue. This was mandated by the authorities on the 787s when it had so many engines issues. SQ also did it on A330s after they had a dual engine surge event (the report about the surge can be found here: https://www.mot.gov.sg/docs/default-sou ... report.pdf )
 
Wacker1000
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Re: Why are engines on planes changed so often?

Tue Mar 16, 2021 3:04 pm

TriL1011Star wrote:
So many times you will hear of an aircraft who is operating with leased engines, or have had multiple engine changes. Why is this? It doesn't seem like a plane is very old when engines start getting swapped out either.


Is it a V2500?
 
CanadianNorth
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Re: Why are engines on planes changed so often?

Tue Mar 16, 2021 3:18 pm

Lots of reasons to switch engines around...

- Keep the airplane flying while an engine is out for repair or overhaul, sometimes operators will have a spare engine ready and if an engine in service needs to visit the repair shop that spare engine will be installed in its place, and then when that engine comes back from the repair shop it will become the spare for next time.

- Not uncommon to do some musical engines on a fleet to spread hours around so you don't have several engines come due for overhaul at the same time.

- Might be an airframe is down for a while for heavy maintenance anyway and another airplane needs an engine now and your spare engine isn't back from the repair shop yet.

- Airlines will sometimes have different engine thrust ratings for a fleet type (different variants of the same thing) and move engines around as they wear out. For example a freshly overhauled CFM56 will likely have no trouble giving 23000lbs of thrust all day for a high weight 737-400 for the first while, but after some years in service it will struggle to stay within the margins. However at that point instead of an expensive overhaul then and there you could instead de-rate it down to 20000lbs and put it on a 737-500 and it'll run that just fine for several more years before actually needing that expensive overhaul.
HS-748, like a 747 but better!
 
Weatherwatcher1
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Re: Why are engines on planes changed so often?

Tue Mar 16, 2021 4:26 pm

How long an engine lasts on wing really depends on engine and operation. A CFM56 can go up to about 40K hours between removals if in the right conditions.

Getting 10K hours out of a GEnx or Trent 1000 isn’t easy. Trent 1000 engines have had to deal with 1000 cycle turbine blade life limits.

https://www.rolls-royce.com/products-an ... on-modules
 
IFlyVeryLittle
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Re: Why are engines on planes changed so often?

Tue Mar 16, 2021 5:38 pm

Doing it by the book, how long to remove an engine? How long to replace one?
 
889091
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Re: Why are engines on planes changed so often?

Tue Mar 16, 2021 8:40 pm

IFlyVeryLittle wrote:
Doing it by the book, how long to remove an engine? How long to replace one?


Approx 6 hrs for a T7

https://www.youtube.com/watch?v=Dp8xmgt1PKc
 
Thrusty69
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Re: Why are engines on planes changed so often?

Tue Mar 16, 2021 11:54 pm

IFlyVeryLittle wrote:
Doing it by the book, how long to remove an engine? How long to replace one?


Many answers there. Depends on the type of engine the type of plane, the components that need to be swapped from the take off engine to the install engine (QEC engines typically have most of the components on the new engine and can reduce engine swap times by half. Easily. I can speak for “most”, and I use that word very loosely... But the Boeing and the Airbus aircraft with a good team of 4-5 mechs should be able to swap one in around 10 hours... other factors include misc parts and tooling on hand, required engine runs (and whether they pass or fail), and potentially a lot of paperwork...

I’m sure someone else will chime in, but if you had a specific aircraft in mind, whether it’s at home or on the road, whether the engine is QEC, than you’ll get a better idea...
 
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CCA
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Re: Why are engines on planes changed so often?

Wed Mar 17, 2021 3:24 am

A quick search found the record for longest time on wing is over 40,000 hours and varies from 9 to 13 years without being removed. Pretty impressive.
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e38
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Re: Why are engines on planes changed so often?

Fri Mar 19, 2021 3:34 pm

TriL1011Star wrote:
So many times you will hear of an aircraft who is operating with leased engines, or have had multiple engine changes. Why is this? It doesn't seem like a plane is very old when engines start getting swapped out either.


TriL1011Star, engine leasing is very common these days, both for large airlines and smaller companies.

First, keep in mind that engines, although very reliable, undergo considerable amount of "wear and tear" and are subject to extreme internal temperature changes, perhaps more than other aircraft components. Also, because of their complexity, they are very expensive.

A leasing program allows airlines to properly direct, and protect, their investments while achieving greater flexibility and reliability, particularly in the event of unscheduled engine maintenance.

Some airlines operate a fleet of aircraft with multiple engine types. I'm aware of some companies--in the U.S.--that operate aircraft with Pratt and Whitney, General Electric, Rolls Royce, and CFM engines, and some with additional sub-types of each of these. It can be very expensive, and perhaps prohibitive, to procure, and store all the engine components necessary for proper engine maintenance.

Here is a quote from wikipedia (I know, not the best source of information, but it's a start), regarding engine leasing, sometimes known as power by the hour:

"A Power by the Hour program provides budget predictability, avoids installing a loaner during repairs when an aircraft part fails and enrolled aircraft may have a better value and liquidity. This concept of unscheduled maintenance was initially introduced for aircraft engines to mitigate engine failures. The term was coined by Bristol Siddeley in 1962 to support Vipers of the British Aerospace 125 business jets for a fixed sum per flying hour. A complete engine and accessory replacement service was provided, allowing the operator to accurately forecast this cost, and relieving him from purchasing stocks of engines and accessories."

That's why you see a fair amount of engine changes. Where at one time an airline would need to repair damage to an engine--or perform scheduled maintenance-- "in house," with an engine leasing program the engine is simply changed.

You may find additional information on this if you Google "aircraft engine leasing," "aircraft engine maintenance," or "aircraft engine power by the hour."

As crew members, we are very aware of the expense of engines and do our best to operate them completely within limits and specifications. On the aircraft I fly, with CFM-56 engines, we strictly adhere to the warm-up and cool down requirements. For first flight of the day, or if the aircraft has been sitting for eight hours or more, we operate the engines at low power (i.e., idle or taxi thrust) for a minimum of 5 minutes before applying takeoff thrust. For flights that are not the first flight of the day, the warm-up requirement is two minutes. After landing, we allow the engines to cool for three minutes before shutdown. There are other engine limitations, of course; this is just an example of methods to improve engine reliability.

e38
 
unimproved
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Re: Why are engines on planes changed so often?

Fri Mar 19, 2021 6:34 pm

IFlyVeryLittle wrote:
Doing it by the book, how long to remove an engine? How long to replace one?

747 is 3 shifts (24h) including inlet and exhaust swap. Most time consuming part is lining up the new one with the pylon and bolts.
 
GalaxyFlyer
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Re: Why are engines on planes changed so often?

Fri Mar 19, 2021 8:27 pm

Many years ago, at EAL, I was at restaurant speaking with an FDX team picking up a EA B727 for cargo conversion—flight crew and a couple of lawyer-accountant types. They stated that they had hung and removed five engines before getting three that were free and clear of liens, just about anybody and everybody owned some piece of the EA engine inventory.
 
Dalmd88
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Re: Why are engines on planes changed so often?

Sat Mar 20, 2021 3:31 pm

IFlyVeryLittle wrote:
Doing it by the book, how long to remove an engine? How long to replace one?

A crew I worked on could do a 757 engine change in less than a 10 our overnight shift. Towed into the hangar at the start of the shift and pushing out for the engine runs right near the end. That was fully prepped QEC change, with an experience crew where everyone knew their tasks.

For the JT8D on the MD-88 we had a spare on site. It always seemed to be set up for the wrong side. It typically took a shift to do the QEC swap to switch sides. I'm sure it could have been done faster, but the goal of down and up in one shift was now not possible so the urgency kind of faded. That airframe also tended to issues with the pylon that could only be noticed once the old engine was down. Not usually anything major but required to be addressed. Parts on hand was usually a limiting factor. The fire seal is bad and we need to ship it up from ATL. The hydraulic fitting bulkhead feed through is worn and now needs a sheetmetal repair.

When I worked in the C check crew it took a lot longer. Drop happened on one shift and then other work was accomplished on the pylon before we would hang the new one.
 
Chemist
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Re: Why are engines on planes changed so often?

Sun Mar 21, 2021 6:17 pm

What is QEC?
 
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fr8mech
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Re: Why are engines on planes changed so often?

Sun Mar 21, 2021 6:50 pm

Chemist wrote:
What is QEC?


Quick Engine Change.

It means the engine is ready to hang and run. Some operators will maintain their spare engines with certain components missing. The expectation is to take these components from the old engine and install them on the new engine. Takes time.

At PanAm, we used to keep a QEC JT9 at Hangar 17. Had everything, including the nose cowl, installed. A crack crew could knock that engine out in less than 8 hours.
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VMCA787
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Re: Why are engines on planes changed so often?

Sun Mar 21, 2021 8:22 pm

TriL1011Star wrote:
So many times you will hear of an aircraft who is operating with leased engines, or have had multiple engine changes. Why is this? It doesn't seem like a plane is very old when engines start getting swapped out either.

I have to ask, why do you think it is so often? Are you comparing the current generation of engines with gen 1? Or what?
 
LCDFlight
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Re: Why are engines on planes changed so often?

Mon Mar 22, 2021 12:56 am

VMCA787 wrote:
TriL1011Star wrote:
So many times you will hear of an aircraft who is operating with leased engines, or have had multiple engine changes. Why is this? It doesn't seem like a plane is very old when engines start getting swapped out either.

I have to ask, why do you think it is so often? Are you comparing the current generation of engines with gen 1? Or what?


I took the question to mean, shouldn't it be incredibly rare for an aircraft to be separated from the engines it was built with. The answer is no. When you are running a fleet of 50 airplanes, 100 engines, you can save money by synchronizing engine wear and maintenance as a total fleet. You make a maintenance plan that results in the highest fleet reliability possible and lowest cost possible. And that solution is not "make sure airplanes always have their original engines on." Nobody cares about that, except lessors when the airplane is being returned or sold at the end of its life.

So it's a cool answer, a little story about problem solving and logistics. I also had the same question at one time.

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