Page 1 of 1

When jetliners are offered with multiple powerplant options, how do they decide which to choose?

Posted: Thu Nov 11, 2021 9:40 pm
by convair880mfan
Sometimes I see that a jet airliner can be bought with either lower or higher thrust powerplants. Usually the higher thrust version of the powerplant are heavier but offer better takeoff performance all other things remaining equal.

The Boeing 737-500 , for example, was offered with either the 18,500 CFM56 or the 20,000 CFM56 powerplants. Seems like the higher thrust 737-500s had better takeoff performance and first segment ROC. Can't find data on payload/range for the two types but am thinking intuitively that the lower thrust version probably had better range for the same payload. Not sure. The Boeing Commerical Airplane site doesn't offer data on payload/range for both the higher and lower thrust 737-500, only the lower thrust version.

And am thinking the higher thrust version most probably had higher fuel consumption. Not absolutely sure of that either though. Looking at Boeing data from their website it looks like the 737-500 with the higher thrust engines had better "hot and high" performance than its lower powered brother.

So when selecting aircraft for their fleets, is powerplant choice mostly a matter of what are the priorities of the buying airline: initial cost, continuing cost, range, performance, payload, and, and, and? Do airlines ever purchase some of a particular type of jetliner with lower thrust powerplants and some with higher thrust for different markets? For example, when SWA had the 737-500, were some higher thrust versions and some lower? Can't seem to find that info with a web search. Probably am not using the right search terms. Thanks for any info, especially authoritative info!

Re: When jetliners are offered with multiple powerplant options, how do they decide which to choose?

Posted: Thu Nov 11, 2021 10:36 pm
by GalaxyFlyer
Our B727s at EAL had D-9, D-15 and D-17R power, Scheduling was good at putting the right airframe and engine configuration where it was needed for performance reasons.

Re: When jetliners are offered with multiple powerplant options, how do they decide which to choose?

Posted: Thu Nov 11, 2021 11:00 pm
by N1120A
WN's -500 were all theirs from factory till retirement, so my guess is they had the same engines. No need to add complexity.

Higher thrust engines don't necessarily mean less range. In fact, they can mean higher range through a higher MTOW. That is certainly true with the 757.

Re: When jetliners are offered with multiple powerplant options, how do they decide which to choose?

Posted: Fri Nov 12, 2021 9:08 pm
by 77west
On the 737-500 you mention, the only difference between the two engines is the rating plug, so there should not be a difference in cruise fuel consumption. Basically, if you pay more, the rating plug allows the engine to deliver more power, at the cost of increased wear & tear and of course fuel consumption when operating at that higher setting, but overall cruise consumption would be similar. Some airlines intentionally derated the airframe/engine combo to reduce landing fees and wear & tear for operations not needing the full capabilities, see Singapore Airlines and their 777-200ER regional versions. Paper derated engines and MTOW. Some were later converted back to full performance -200ER standards. Some paperwork and a rating plug change and you are done.

Re: When jetliners are offered with multiple powerplant options, how do they decide which to choose?

Posted: Sat Nov 13, 2021 1:35 am
by convair880mfan
That is very interesting, 77west. Can you or someone else elaborate on "rating plugs." Are these the same as "ID" plugs. ?

http://nandang-smart.blogspot.com/2014/ ... -plug.html

I wonder if the DC-10-15s for "hot and high" airports used what you call "rating plugs" on those CF6 powerplants?

Re: When jetliners are offered with multiple powerplant options, how do they decide which to choose?

Posted: Sat Nov 13, 2021 2:32 am
by celestar345
convair880mfan wrote:
That is very interesting, 77west. Can you or someone else elaborate on "rating plugs." Are these the same as "ID" plugs. ?

http://nandang-smart.blogspot.com/2014/ ... -plug.html


That's the one.

Give the engine manufacturer some money, and they will give you a little box with the rating plug and a new ident plate.

Similar to nowadays you pay money on internet, and you receive a little gadget. Plug it into your car and get more power.

Re: When jetliners are offered with multiple powerplant options, how do they decide which to choose?

Posted: Thu Nov 18, 2021 11:35 am
by vhqpa
convair880mfan wrote:
I wonder if the DC-10-15s for "hot and high" airports used what you call "rating plugs" on those CF6 powerplants?


I believe the DC-10-15s used CF6-50 engines, instead of the CF6-6 engines on the 10 series. So it was essentially a DC-10-10 with DC-10-30 engines. As I understand it the CF6-6, and CF6-50 had physically different core configurations, rather than a different rating plug like the thrust variations with the already mentioned CFM56 series on the 737.

Re: When jetliners are offered with multiple powerplant options, how do they decide which to choose?

Posted: Fri Nov 19, 2021 3:36 am
by 77west
vhqpa wrote:
convair880mfan wrote:
I wonder if the DC-10-15s for "hot and high" airports used what you call "rating plugs" on those CF6 powerplants?


I believe the DC-10-15s used CF6-50 engines, instead of the CF6-6 engines on the 10 series. So it was essentially a DC-10-10 with DC-10-30 engines. As I understand it the CF6-6, and CF6-50 had physically different core configurations, rather than a different rating plug like the thrust variations with the already mentioned CFM56 series on the 737.


Correct, they were similar but physically different engines, the CFM56 comparison would be between the -3 (737 Classic) and -5 (A320) as an example

The CF6-50 was a newer, more powerful version developed for the medium-long range DC10-30 (And also used on the B747 and A300) rather than just a high-rated example of the same engine.

Re: When jetliners are offered with multiple powerplant options, how do they decide which to choose?

Posted: Sat Nov 20, 2021 12:53 am
by LMP737
Whose bank rolling you has a part in it as well. GE is a big creditor for AA, I'm going to guess this had a role in their decision to pick the GenX for their 787 fleet.

Re: When jetliners are offered with multiple powerplant options, how do they decide which to choose?

Posted: Sun Nov 21, 2021 10:25 pm
by Canuck600
Pats commonality is another issue as well; nobody really wants to stock parts for a small # of engines that are totally different than the majority of the other engines in the fleet. Purchasing smaller quantities of parts means the cost part is higher then if you wre purchasing in larger volumes.

Re: When jetliners are offered with multiple powerplant options, how do they decide which to choose?

Posted: Mon Nov 22, 2021 7:17 pm
by flybaurlax
Commonality between fleet types is a big factor. Consider A320 family operators that have the CFM56-5B engines, and started to operate NEO A320 fam aircraft. The LEAP-1A would be a clear choice over the P&W GTF, as that customer already has experience and service history with Safran/GE. It certainly helps to be able to leverage the same relationships from older engine models to the new ones.

Re: When jetliners are offered with multiple powerplant options, how do they decide which to choose?

Posted: Tue Nov 30, 2021 2:35 pm
by lightsaber
celestar345 wrote:
convair880mfan wrote:
That is very interesting, 77west. Can you or someone else elaborate on "rating plugs." Are these the same as "ID" plugs. ?

http://nandang-smart.blogspot.com/2014/ ... -plug.html


That's the one.

Give the engine manufacturer some money, and they will give you a little box with the rating plug and a new ident plate.

Similar to nowadays you pay money on internet, and you receive a little gadget. Plug it into your car and get more power.

Just a nitpick, the new plug has a new maintenance interval as increased thrust reduces engine life.

If the thrust isn't needed, the cost savings of the reduced maintenance is worth it as the number of cycles between overhauls goes up. Going from memory, on the 737-400, this is the difference between 14,000 cycles and 20,000 cycles or for a $1.6 million overhaul, the difference between $228.57 per takeoff or $160. While $68.57 isn't much and will be compensated some by reduced climb fuel burn (assuming climb thrust is increased as getting up to cruise quickly is the most fuel efficient). Is there a business reason for the thrust. If yes, buy it. If no, save on maintenance.

Lightsaber