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If, for example, an operator has a Boeing 737-800 with CFM56-7B engines set at a 22K thrust rating, but the next operator wanted to operate the engines at 24K thrust rating, what would they need to physically do to the aircraft in order to change this?

Would it involve the engine going to the shop for certain components replacement, or is it as simple as a FADEC reprogram? I've noticed the life of certain engine components differ depending on the thrust rating used so I wondered how the engine is converted to these different configurations?

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Please refer to the following website, it explains the plug programming.:

http://nandang-smart.blogspot.com/2014/09/cfm56-7b-identification-plug.html

You may read:

WHEN ENGINES ARE MOVED BETWEEN AIRCRAFT AND MAY REQUIRE A DIFFERENT THRUST INSTALLATION THIS N1 MODIFIER IS USED IN CALCULATIONS TO UPRATE OR DERATE A GIVEN ENGINE AT AN APPROPRIATE LEVEL.

You may also read

THE THRUST LEVEL OF AN ENGINE IS CHANGED (PERHAPS MORE ACCURATELY "PROGRAMMED") BY INSTALLING A "ID PLUG" THAT SCREWS ONTO THE EEC AND CONVEYS PROGRAM INFORMATION THAT SETS THE ENGINE THRUST OUTPUT TO THE LEVEL DESIRED BY THE OPERATOR.

With respect to the thrust limit, you may display on the CDUs ( MCDUs) the FMS thrust limit page that allows the pilots to derate the TO thrust.

The following website shows for the B777 how to get access to the «  thrust limit » page:

So the pilot may change the thrust limit from the CDU, while the rating is changed by pin programming on the plug, the value entered in the CDU by the pilot is transmitted to the FMS which will ask the FADEC to reduce the thrust whatsoever below the rated value chosen by the operator by pin programming.

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For the CFM56-5B series, it is as follows:

The Airbus A320 family is powered by two CFM International CFM56-5B turbofan engines. These engines can produce a thrust from 21600 lb (9800 kg) to 33000 lb (14970 kg) depending on the aircraft version set by the engine data programming plug.

and

All the engines are basically the same. A programming plug on the Electronic Control Unit (ECU) changes the available thrust.

Source: Airbus Single Aisle Technical Training Manual

Keep in mind the engine has its own certification. So if the 22K operator in your example did not have the 24K certification, it may not be as simple as depicted in the quotation.

Although the 5B series comes in 9 variants with 5 different bypass ratios, the FADEC manages that by adjusting the variable stators, limiting or increasing the air reaching the core.

The 7B should be similar, but I don't have a reference for it.

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From Wiki

From the wikipedia page for the CFM56-engine: notice that the different thrust ratings are specified per aircraft type, with for instance the 737-700 having been delivered with four different ratings. The engine hardware for a model number does not change, a reduced maximum rating is indeed just a different circuit board inside the FADEC.

The smaller versions have a lower thrust rating because of the shorter moment arm between vertical tail and engines: upon engine fail, the rudder authority is less and can therefore only compensate for a lower max. thrust.

This article mentions the various ratings, thrust limits, derating etc that are applicable to fixed wing and rotary wing aircraft. Notice the use of the word "rating":

The only 2 thrust ratings that airplane jet engines are certified for are maximum takeoff (MTO) and maximum continuous thrust (MCT). All other thrust ratings —such as(ground/flight) idle, climb and cruise thrust— are only figures recommended or set by the engine manufacturer.

enter image description here

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  • $\begingroup$ Beyond what @ymb1 points out about engine certificates, the aircraft type certificates specify the engine model and thrust ratings. The Boeing 737 TCDS provides the approved engine models and thrust options. Operators can't change the engines or thrust ratings without an STC. $\endgroup$ – Gerry May 29 at 17:50
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Operators cannot change thrust ratings, they can only change thrust limits. If you want higher thrust on your aircraft than the max thrust rating, you have to look at the aircraft type certificate, see if it was certified with an engine or engine mechanical configuration with a higher thrust rating, and if so, swap the engines or convert the engine to a new model configuration. If there is no engine or configuration listed in the TC with a higher thrust rating, then you have to pursue an expensive STC.

I suspect you are confusing thrust ratings (which are design limits from the manufacturer) with thrust limits, which are programmed in the FADEC. Two different things. A turbine engine may be rated for a certain thrust, but be limited to a lower MTO because of the aircraft in which it is installed. The former is fixed and documented on the engine data plate (along with the current configuration of the engine), the latter is programmed into the FADEC.

Turbine engines such as those used on the B737-800 have only two approved thrust ratings, the MTO (max takeoff thrust) and MCT (max continuous thrust). Everything else from there to idle are just manufacturer recommendations. The engines on the -800 are CFM56-7B engines rated at between approximately 18,500 and 34,000 pounds thrust within 49 different model numbers, as listed in the TCDS (Type Certificate Data Sheet). If an operator wants their engines to last, and minimize repair maintenance costs, they will do things like not push the engines to MTO when it is not needed, and less thrust will do.

When anyone adjusts thrust in the FMS for a particular situation, for example, what they are doing is NOT changing thrust rating. What they are doing is changing thrust limits, which the FMS them communicates to FADEC so it knows how to respond to pilot inputs in the throttle quadrant.

For those of you can deal with the FAA's technospeak, AC 33.7-1 goes through the process that an aviation turbine engine manufacturer must follow to obtain type certification, and explains the difference between thrust ratings and operating limitations. In essence, this confirms what I have already stated -- operators cannot change thrust ratings because that would require a new certification process for the engine, with all that that entails. Only limits can be changed and then again strictly within the performance envelope specified in the type certificate.

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    $\begingroup$ Why is this answer rated so low, it gave a valid explanation that there are hard thrust ratings that you can't change and adjustable thrust limits that can be changed via FMC. $\endgroup$ – Jan Jun 1 at 8:21
  • $\begingroup$ @Jan, please note the following: « When engines are moved between aircrafts and may require a different thrust installation the pin programming N1 modifier is used in calculations to uprate or down rate a given engine at an appropriate level, this has nothing to do with the physical maximum capabilities of the engine. » $\endgroup$ – user40476 Jun 5 at 13:13
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    $\begingroup$ Why does this answers get delete votes? People may think it is wrong, but that is what the voting system should be used for. Please be reminded that there are two reasons for deleting a question: 1) The answer is extremely low quality: There is little to no scope for improvement. 2) The answer doesn't attempt to answer the question; it may be a comment or a separate question altogether. Neither reason applies to this question in my opinion. $\endgroup$ – DeltaLima Jun 5 at 14:13
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    $\begingroup$ Hi Juan, this answer is getting better by the minute. Are you perhaps confusing operators with flight crew in your answer? The flight crew (= pilots) can indeed only change the thrust limits (through the FMS), but the operator (airline) can change the thrust ratings (by making their maintenance organisation change the engine configuration, software and paperwork) as explained in your first paragraph (bar the first sentence). $\endgroup$ – DeltaLima Jun 5 at 15:44
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    $\begingroup$ @Juan Jimenez, For clarification, the max 100% thrust that shows on the FMS « thrust limit » page corresponds to what is decided by pin programming by the operator and not to the max physical rating of the engine, therefore as an exemple when the pilot reduces the thrust to 90%, it is 90% of what the operator has chosen by pin programming and not 90% of the max physical limit of the engine. $\endgroup$ – user40476 Jun 5 at 17:20

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