737 CL Derate confusion

[allison]

Please help... i am flying a 734 with 23.5k engines. Recently, my company told me that the engines have been derated to 22k. And that if required, i can simply disconnect the auto throttle and manually set, via the relevant tables, the 23.5k N1 setting. The options are not available to me on the FMS, only 22k is available. I am confused because i understood that it was a maintenece procedure? I will appreciate any explanations asap, cause we flying heavy loads that require the 23.5k thrust to get airborne. Thx...

[flyingchanges]

Not sure about your operation, but if we use 27K (26K rated) more than our allotment, it costs us millions per engine.

[FlyingStone]

Recently, my company told me that the engines have been derated to 22k. And that if required, i can simply disconnect the auto throttle and manually set, via the relevant tables, the 23.5k N1 setting. The options are not available to me on the FMS, only 22k is available.

Change of company might be the smartest idea here...

Back on topic: if the CFM56-3C1 engine is fixed derated to 22K by FMC pin programming, that's the maximum thrust you can use for takeoff. The engine will and should be able to achieve 23.5K (and more in case of firewalling thrust levers) thrust rating even if derated to 22K, but you invalidate quite couple of things.

First, the -3C1 derate to 22K on -400 is usually done to comply with Chapter 3 noise certification. Second, the engines might be derated to prolong their on-wing life. In this case, the EGT margin should be enough for 22K operation, but you could find yourself busting EGT limits on takeoff with 23.5K rating, just because engine condition is insufficient for 23.5K rating operations. Third, if the company has complied with the SB for engine thrust reduction, than you should get new manuals from Boeing with performance data only for 22K (and perhaps 20K, but not 23.5K).

If you really need the 23.5K derate, just complete an action in the same SB that is used for derating the engine and you get your maximum thrust rating back - but I suppose there are some reasons why you have 22K rating and company is "suggesting" use of 23.5K with (by Boeing) unapproved methods.

[Whitebeaches]

Check the init ref page and see what the Eng rating is in the FMC. This is the rating of the engine, do not exceed this power setting by turning off the autothrottle. Take care of the engines and they will take care of you, use as much reduced power as possible. We currently have a 737-300 that has 22K permanently derated to 20K, due to high temps at full power for 22K. This will save the company a lot of money by not having to overhaul.
Hope this make sense to you, please do not over temp by setting power with autothrottle off http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/thumbs.gif

[c100driver]

Your company needs to purchase 23.5 K thrust!

Are they lease engines? They may be trying to cheapen the lease cost by stipulating a lower rating but then manually using a higher thrust!

[allison]

This is my understanding. The FMC should give you two options for derate - TO-1 and TO-2. In this case, it does not, only 22k figure is available on the inet ref pg. If you have 23.5 k engines it means TO-1 - 22 k and TO-2 - 20 k.
The FMC has only has the one option for derate, which means that the engine is already derated to 22k and so can only be derated to 20 k.

This means that maintenance electronically derated de engine to 22 k, and the option of firewalling the thrust levers to get 23.5 k is not realistic, although that's what they say I have to do.

They have to go to the engine and electronically rate it back to 23.5 k.
You will know that you are at 23.5 k thrust engines, when you get TO-1 and TO-2 options on the FMC. Without that you are on 22 k engines.

I have not seen the SB and in the interst of safety, I want to understand better that if I set 23.5k N1 thrust by diconnecting the A/T and of course observing the EGT limitation, which is going to be the most restrictive for me, due to the high alt and temp, that the a/c will perform as required and iaw the rtow tables for 23.5k thrust???

[FlyingStone]

This means that maintenance electronically derated de engine to 22 k, and the option of firewalling the thrust levers to get 23.5 k is not realistic, although that's what they say I have to do.

You don't have to firewall -3C1 engine to get 23.5K even if it's derated to 22K. Firewalling will get you more than 23.5K thrust.

I want to understand better that if I set 23.5k N1 thrust by diconnecting the A/T and of course observing the EGT limitation, which is going to be the most restrictive for me, due to the high alt and temp, that the a/c will perform as required and iaw the rtow tables for 23.5k thrust

If you are asking if the engines will deliever 23.5K thrust to achieve normal 23.5K performance - yes. If you are asking whether this is even remotely legal or smart - NO.