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brian415
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Different manufacturers for jet engines #1 vs. #2

Wed Mar 24, 2021 4:52 am

I think I recall from past discussions that engines from different vintages (e.g. line numbers 500 and 900) of the same make/model are allowed on a given airplane.

Are airlines allowed to mix/match engines even further and do unusual combinations? Examples:

  • PW4090 for engine #1; PW4098 for #2
  • GEnx-1B for engine #1; RR Trent 1000 for #2

If not allowed for actual flights, are they allowed in special circumstances such as ferry flights (e.g. flying to a maintenance base with a borrowed engine)?

Tanks.
 
mxaxai
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Re: Different manufacturers for jet engines #1 vs. #2

Wed Mar 24, 2021 9:03 am

No, it is generally required that all engines be of the same model and thrust rating, unless the aircraft is specifically certified for a certain combination.
The reengined 727 "Super 27" keeps the old (smaller) center JT8D but uses the newer JT8D-200 for the no. 1 and 3 engines. The HS Trident 3B had a tiny 4th engine to provide extra thrust on take-off.

It is technically possible to switch the engine type (for all engines) but I've never seen it happen in practice, except for newer, slightly improved variants of the same engine.
The only other exception would be major retrofit programs like the DC-8-72/73 or the 727 with newer JT8D engines. It's a lot of work, both to certify and to install the new engines.

Engine manufacturers sometimes test their engines by replacing one of the regular engines on a quad. That's strictly for test purposes only, though.
 
mxaxai
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Re: Different manufacturers for jet engines #1 vs. #2

Wed Mar 24, 2021 9:39 am

One example did come to mind where both engines were swapped: The A319NEO prototype was first flown and certified with CFM LEAP engines, and later fitted with PW1000G engines to certify that configuration.
 
Wacker1000
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Re: Different manufacturers for jet engines #1 vs. #2

Wed Mar 24, 2021 10:23 am

brian415 wrote:
If not allowed for actual flights, are they allowed in special circumstances such as ferry flights (e.g. flying to a maintenance base with a borrowed engine)?


Never because it is physically impossible and a completely uncertified and untested configuration. It takes substantially less time and money to ship an engine than it would to remove an engine/install an engine/ferry an aircraft/remove an engine/install an engine. It isn't uncommon to do something like that with a borrowed spare but that spare is rarely an engine.

You have mechanical differences that would prevent it - pylons almost always have some differences based on engine type, you have different inlet cowls, fan cowls, and thrust reversers
Engine control architecture is never the same between engine manufacturers - IE: GE's use of N1 vs. RR's use of EPR to determine thrust, EEC interface with airframe systems, fire system controls and indication, thrust reverser controls and indication, engine bleed controls, no way to deal with asymmetric thrust, the list goes on
Aerodynamic differences - There are usually differences on the same airframe type with different engine types such as vanes to help control airflow across the wing - mixed configurations are untested and you don't know the result

The closest you would ever get would be with a derate of the same engine type like a CFM56-3B1 on one wing and a CFM56-3B2 on the other. The B2 would be pinned to make the same thrust as a B1.
 
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LAX772LR
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Re: Different manufacturers for jet engines #1 vs. #2

Wed Mar 24, 2021 10:33 am

It can even be hazardous to fly with different PIPs/iterations of the same engine, on a single aircraft.

IINM, that's what happened with TS236 (fuel starved A330 on the TATL)
 
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DarkSnowyNight
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Re: Different manufacturers for jet engines #1 vs. #2

Wed Mar 24, 2021 11:49 am

mxaxai wrote:
Engine manufacturers sometimes test their engines by replacing one of the regular engines on a quad. That's strictly for test purposes only, though.



Nice center gear, there...


mxaxai wrote:
One example did come to mind where both engines were swapped: The A319NEO prototype was first flown and certified with CFM LEAP engines, and later fitted with PW1000G engines to certify that configuration.


This seems more likely to happen on prototypes. CX's B-HNL was swapped to RR Trent 800s when put into service as well.
 
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armagnac2010
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Re: Different manufacturers for jet engines #1 vs. #2

Wed Mar 24, 2021 12:23 pm

During certification, intermixability of different engine configuration is defined on a case-by-case basis, after a review of their airplane effects. The general, basic assumption is to ensure engine performance is within the required enveloppe.

For instance, different FADEC / EEC / etc. software releases might have different cockpit effects, if they effect indication. This might prevent intermixability, as the crew cannot be expected to cope with different system behaviour, and thus have different reactions, based upon which side is affected.

Hardware differences follow the same principles, and are actually less demanding, depending upon their effects. PIP might improve performance, but the difference might be actually less than between 2 identical engines with different life remaining, one close to the shop visit and the other just overhauled. Typically, the 'old' one will displya slighlty higher thrust, higher EGT, higher consumption.

Another aspects is the ability to go back to earlier configuration, to allow installing it with an unmodified engine (for instance, downgrading a software release if intermixability is not allowed). In some cases this is forbidden, if the software release actually solves some issues). The Service Bulletin or regulatory documentatyion (TCDS, eventually AD), will provide information.

On a lighter note, nobody ever tried to certify mixed configuration, GE on one side, RR on the other (for example). It would meet dissimilarity principles, by making a simultenaous design/production error less likely on both sides. But the handling of the whole thing will be definitively odd...
 
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armagnac2010
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Re: Different manufacturers for jet engines #1 vs. #2

Wed Mar 24, 2021 12:27 pm

IINM, that's what happened with TS236 (fuel starved A330 on the TATL)


Nope. TS236 was incorrect configuration on the same engine; 2 incompatible Service Bulletins were embodied (or an approved configuration, my memory fails me), resulting in a pipe chaffing against something else, leading to a massive fuel leak. The other engine had nothing to do with it.
 
WayexTDI
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Re: Different manufacturers for jet engines #1 vs. #2

Wed Mar 24, 2021 2:53 pm

armagnac2010 wrote:
IINM, that's what happened with TS236 (fuel starved A330 on the TATL)


Nope. TS236 was incorrect configuration on the same engine; 2 incompatible Service Bulletins were embodied (or an approved configuration, my memory fails me), resulting in a pipe chaffing against something else, leading to a massive fuel leak. The other engine had nothing to do with it.

Per Wikipedia:
The investigation revealed that the cause of the accident was a fuel leak in the #2 engine, caused by an incorrect part installed in the hydraulics system by Air Transat maintenance staff as part of routine maintenance.[6] The engine had been replaced with a spare engine, lent by Rolls-Royce, from an older model which did not include a hydraulic pump. Despite the lead mechanic's concerns, Air Transat authorized the use of a part from a similar engine, an adaptation that did not maintain adequate clearance between the hydraulic lines and the fuel line. This lack of clearance, on the order of millimetres from the intended part,[6] allowed chafing between the lines to rupture the fuel line, causing the leak. Air Transat accepted responsibility for the accident and was fined 250,000 Canadian dollars by the Canadian government, which as of 2009 was the largest fine in Canadian history.[6]

Chaffing did happen, but the engine was indeed a (slightly) different model.
 
Flow2706
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Re: Different manufacturers for jet engines #1 vs. #2

Wed Mar 24, 2021 3:26 pm

For the A320 CEO there is a thing called "engine intermix". However this does not refer to different engine types, but to different versions of the same (CFM56-5) engine. This intermix is usually not really not noticeable to the pilots, except that the EGT/N1 might be a bit different between the engines. There are some considerations for abnormal operations, but nothing significant. It is impossible to do an intermix between the CFM56 and the IAE V2500, they have quite different characteristics. Also the V2500 uses EPR as the primary engine parameter, whereas the CFM56 uses N1.
 
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Ruddman
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Re: Different manufacturers for jet engines #1 vs. #2

Thu Mar 25, 2021 6:55 pm

I believe the 747 - Classic and 400 - could intermix engines but only of the same manufacturer. i.e couldn’t mix a RR engine with 3 Pratt’s.
But it could fly with different thrust ratings I believe - 3 x 7J and 1 x 7Q etc.
 
StereoTechque
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Re: Different manufacturers for jet engines #1 vs. #2

Fri Mar 26, 2021 7:15 am

DarkSnowyNight wrote:
mxaxai wrote:
Engine manufacturers sometimes test their engines by replacing one of the regular engines on a quad. That's strictly for test purposes only, though.



Nice center gear, there...


Hehe, Very observant! Looks like Airbus permanently deactivated Centre gear on this one as this bird might never load upto it's Max MTOW.
 
mxaxai
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Re: Different manufacturers for jet engines #1 vs. #2

Fri Mar 26, 2021 9:27 am

StereoTechque wrote:
Hehe, Very observant! Looks like Airbus permanently deactivated Centre gear on this one as this bird might never load upto it's Max MTOW.

Not permanently, just for the engine tests. I'm not entirely sure why.

The aircraft is currently used as a testbed for aerodynamics and other systems.
 
IFlyVeryLittle
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Re: Different manufacturers for jet engines #1 vs. #2

Fri Mar 26, 2021 12:28 pm

Would you hang a 200 horsepower Mercury outboard next to a 235 horsepower Evinrude on the back of an offshore fishing boat?
 
Clydenairways
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Re: Different manufacturers for jet engines #1 vs. #2

Fri Mar 26, 2021 4:26 pm

I'm fairly sure i recall that on the DC-9 that you could intermix -7 and -9 engines on the same aeroplane, so probably the 737-200 you could do it as well.
 
GalaxyFlyer
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Re: Different manufacturers for jet engines #1 vs. #2

Sat Mar 27, 2021 2:56 am

Clydenairways wrote:
I'm fairly sure i recall that on the DC-9 that you could intermix -7 and -9 engines on the same aeroplane, so probably the 737-200 you could do it as well.


You could on the B727, but the question different engine manufacturers—JT9-D on one and CF-6 on the other side.
 
VSMUT
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Re: Different manufacturers for jet engines #1 vs. #2

Sat Mar 27, 2021 3:15 am

Several prototypes have been swapped from one engine manufacturer to another prior to delivery. Some A380s I believe, don't remember if some 787-8s were as well.

Original plans for the 787 was for the engines to be easily swappable within hours (from GE to RR or back again), and even to fly with one of each. That plan was scrapped pretty early on.

mxaxai wrote:
StereoTechque wrote:
Hehe, Very observant! Looks like Airbus permanently deactivated Centre gear on this one as this bird might never load upto it's Max MTOW.

Not permanently, just for the engine tests. I'm not entirely sure why.

The aircraft is currently used as a testbed for aerodynamics and other systems.


It's a feature on the A340, it can be deactivated by the crew if the aircraft is light. If the aircraft is empty, it doesn't even contact the ground.

Image
 
Thrusty69
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Re: Different manufacturers for jet engines #1 vs. #2

Sat Mar 27, 2021 4:42 am

It's a feature on the A340, it can be deactivated by the crew if the aircraft is light. If the aircraft is empty, it doesn't even contact the ground.

Image[/quote]


I’ve never seen that switch in the cockpit. What panel number is it on?

A340’s I work on are empty between flights and I’ve never seen center gear come off the ground.
 
FlyHossD
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Re: Different manufacturers for jet engines #1 vs. #2

Sat Mar 27, 2021 2:05 pm

brian415 wrote:
I think I recall from past discussions that engines from different vintages (e.g. line numbers 500 and 900) of the same make/model are allowed on a given airplane.

Are airlines allowed to mix/match engines even further and do unusual combinations? Examples:

[list]
[*] PW4090 for engine #1; PW4098 for #2...


According to my contacts, it was somewhat common for a PW4090 to be placed on on a B777A, with the engine derated to the PW4077 standard. In this case, the 4090 is referred to as a 4077D with thrust akin to the 4077. This practice is known as inter-mixing.
 
deltal1011man
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Re: Different manufacturers for jet engines #1 vs. #2

Mon Mar 29, 2021 6:08 am

FlyHossD wrote:
brian415 wrote:
I think I recall from past discussions that engines from different vintages (e.g. line numbers 500 and 900) of the same make/model are allowed on a given airplane.

Are airlines allowed to mix/match engines even further and do unusual combinations? Examples:

[list]
[*] PW4090 for engine #1; PW4098 for #2...


According to my contacts, it was somewhat common for a PW4090 to be placed on on a B777A, with the engine derated to the PW4077 standard. In this case, the 4090 is referred to as a 4077D with thrust akin to the 4077. This practice is known as inter-mixing.

This happens pretty frequently.

You'll see a Prat 2040 operate on international 752 or a 753 then at about 2/3s of its life it will come off, a new engine from the shop goes on and then the old engine is derated down to 2037 and put on a domestic 752. It will stretch out the TBOs on the engine and increase on-wing time. Thus saving money.
 
LH707330
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Re: Different manufacturers for jet engines #1 vs. #2

Tue Mar 30, 2021 1:25 am

deltal1011man wrote:
FlyHossD wrote:
brian415 wrote:
I think I recall from past discussions that engines from different vintages (e.g. line numbers 500 and 900) of the same make/model are allowed on a given airplane.

Are airlines allowed to mix/match engines even further and do unusual combinations? Examples:

[list]
[*] PW4090 for engine #1; PW4098 for #2...


According to my contacts, it was somewhat common for a PW4090 to be placed on on a B777A, with the engine derated to the PW4077 standard. In this case, the 4090 is referred to as a 4077D with thrust akin to the 4077. This practice is known as inter-mixing.

This happens pretty frequently.

You'll see a Prat 2040 operate on international 752 or a 753 then at about 2/3s of its life it will come off, a new engine from the shop goes on and then the old engine is derated down to 2037 and put on a domestic 752. It will stretch out the TBOs on the engine and increase on-wing time. Thus saving money.

Same thing with the CF6 at NZ and the RB211 at BA: they often started on the 767-300ERs, then as they got older they rotated out to the 747-400 where range was less of a problem.
 
VSMUT
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Re: Different manufacturers for jet engines #1 vs. #2

Tue Mar 30, 2021 10:52 am

Thrusty69 wrote:
I’ve never seen that switch in the cockpit. What panel number is it on?


You pull the breaker.
 
WIederling
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Re: Different manufacturers for jet engines #1 vs. #2

Thu Apr 01, 2021 9:54 am

WayexTDI wrote:
Chaffing did happen, but the engine was indeed a (slightly) different model.


using incompatible parts for a repair != incompatible unmatched engines as cause.
 
stratclub
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Re: Different manufacturers for jet engines #1 vs. #2

Fri Apr 02, 2021 10:33 pm

VSMUT wrote:
Thrusty69 wrote:
I’ve never seen that switch in the cockpit. What panel number is it on?


You pull the breaker.
Is a form 1 entry required in the logbook?
 
stratclub
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Re: Different manufacturers for jet engines #1 vs. #2

Fri Apr 02, 2021 10:46 pm

The 5th engine transportation pod was available as late as the 400.
Image
 
WayexTDI
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Re: Different manufacturers for jet engines #1 vs. #2

Mon Apr 05, 2021 11:50 pm

WIederling wrote:
WayexTDI wrote:
Chaffing did happen, but the engine was indeed a (slightly) different model.


using incompatible parts for a repair != incompatible unmatched engines as cause.

I never said the engines were not compatible; the slightly different model engines lead to incompatible part combination, which lead to chaffing, which lead to leak, which lead to glider.

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