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Engine Commonality

Mon Jun 26, 2000 1:09 pm

I'll post this question on its own thread since it didn't really fit in earlier.

How much commonality do jet engines of the same manufacturer have with each other?

We always hear on this forum people arguing that an airline that has PW powered jets in its fleet will power their newly ordered jets with PW as well, etc. because of commonality. How is this possible? Over the years, most of the reason that planes are more efficient today is because of great strides taken in powerplant technology. So, the question is, how similar is the CFM56 to the CF6 and GE90, all made by GE/Snecma, but at different time periods. To go further even, how similar are the CFM56-3 and CFM56-7 which are different time periods, and different power ratings?

Also, we hear on this forum much about how UA with its large PW powered fleet buys V2500 powered 320s because IAE, the makers of the V2500 has PW as a partner, and thus they have commonality with the other PW engines in the fleet. Similarly, we hear that BA with its large RR powered fleet buys V2500 powered 320s because IAE has RR as a partner, and thus they have commonality with the other RR engines. So, how can this be? How much commonality can an IAE engine have with both RR and PW at the same time? Can a mechanic trained on the V2500 work on a PW4000 and know what's going on? How about an RR Trent?

Any input would be much obliged. (Thanks in advance!)
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RE: Engine Commonality

Mon Jun 26, 2000 1:55 pm

DLX, usually engines in the same "family" have a greater amount of commonality than those outside of the family. For example, PW, the PW4000 family probably wont have much in common with the PW6000 family. Even within the family it could get "uncommon". Again, PW as an example, a higher thrust PW4000 for say the 777X models would be a new engine and not have much in common with its lower thrust brothers.

Now, when people say that "United bought IAE because of PW's particiaption" or "British Airways bought IAE because of RR's participation" the advantage here is usually price. Because United is such a large PW operator, it is probably easier for them to get a better deal on a PW engine (even if its just a partner) than it would to go to GE for the first time and make a deal. Same with BA/RR. The CFM, CF6, and GE90 have very little in common with each other, but look at Continental or Air France, they are both large GE operators, and can say "Hey, we are buying the 777, how about a deal on GE90, after all, we did just buy around 300 CFM56 engines from you."

There is one thing though, technologies learned building one engine, may of course be applied to other non common models. This however does not necessarily make the engines common. One example is the BR710/715, which I believe, correct me if I am wrong people, has some V2500 technologies, but by no means are the engines similar or a common type.

Hope this helps.

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RE: Engine Commonality

Mon Jun 26, 2000 1:57 pm

Man, that's a tough question. It begs one as well--How do we define commonality? In the broadest of terms maybe a CFM56 can be considered similar to a CF6, but I work on both and I don't see much commonality other than basic layout...it's just my opinion. Even the same type engines can have differences (FADEC or no?) CF6's come in both flavors. The 737 and A32X CFM's aren't very much alike to my eyes, even discounting the Airbus' FADEC system. As I see it, commonality has a greater appeal due to the economies of manufacturing and maybe parts procurement than the mechanic's familiarity--though in theory it can be a factor. Engine/Aircraft systems knowledge is not a zero-sum game from manufacturer to manufacturer. Many of the same theories apply from engine to engine and so learning about PW2000 systems is not going to erase my memory of RB211's. JT8's on a DC9 have differences from those used on Boeings but the theory's the same--even if Brand X has a different name for a part of the same function than Brand Y. The parts may be physically different but their function and theory is similar -- . This is not to say one can shoot from the hip and "wing it" without referrng to a manfacturer's specific proceedures but it gives some perspective. In short, I don't have a problem with commonality or lack thereof. I'm not sure I've answered your question, but then I'm not sure how broad or specific an answer you were looking for. Take care.
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RE: Engine Commonality

Mon Jun 26, 2000 11:05 pm

Is it possible for mechanics to have a common main. cert. on (for example) all PW4000 type engines , or are the engines within the type different enough to justify seperate maint. ratings?

And, if so, does this spread across engine types - can a mechanic certified to work on the PW4000 series work on a PW6000, and how much training would be required vs a new certification on the PW6000?

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RE: Engine Commonality

Mon Jun 26, 2000 11:28 pm

I don't know. Only an example I know:
Swissair has: on its A 320 family CFM56 engines; on the A 330-200 and MD 11 P&W 4168 and 4462; on the A 340-600 RR Trent 500. This means they will have an all airbus fleet (when the MD 11s are gone in 2005) with engines of three different manufacturers. I dont think that engine commonality is very important.
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RE: Engine Commonality

Tue Jun 27, 2000 12:20 am

The "maintainance rating" asked about may be an issue in Europe or elsewhere, but in the United States you can work on anything -- that is, you do not have to be "certified" on every type of plane/engine. It behooves him and the airline he works for for that airline to have in-house training covering the aircraft/engine/systems for farmiliarity, proceedural, and troubleshooting purposes, and technically it's required. Most airlines have a training dept to to so,or train mechanics from other airlines that do not have the training facilities on a contractual basis.

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