PPRuNe Forums - thrust modes CRZ/CLB Boeing 737

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thrust modes CRZ/CLB Boeing 737

I have a question what is the difference between the two thrust modes isn't max. CRZ thrust the same as max. CLB thrust? I don't see the difference and no explanation in the FCOM?:confused:

Max CLB vs Max CRZ

The difference the two, I think, is the wording. More often than not the max CLB and CRZ N1 values are usually the same or almost the same but the FMC calculates and decides the value of each during the respective phase of flight depending on the prevailing conditions.

yes but what is the benefit of max CRZ? I realized that max CLB is always more than max CRZ but isn't it possible to set max climb whenever I want?

Quote from my idiots' guide to 73NG FMC:

"You may want to change the N1 limit

-from CRZ to CLB during criuse in mountain wave

- from CRZ to CLB when flying above optimum altitude

-from CRZ to CLB during hold at high altitude

-to max CON during an engine-out situation"

Any help?

CRZ is usually about 5% less than the other N1 settings when at cruise.

If I get in to mountain wave, I'll select CONT.

Quote:

maximum cruise thrust

This thrust rating is used as a reference for the thrust available for cruise. It is not a true limit on cruise thrust, as the engines can be advanced to maximum continuous thrust in an emergency situation. It is usually designated as MCRT. It’s usually a slightly lower thrust rating than maximum climb thrust, although in some instances the two are the same. There is no time limit on the use of
maximum cruise thrust.

Cruise is normally conducted at a thrust setting somewhat less than maximum cruise thrust. MCRT is the upper cruise thrust threshold for normal operation. Should the pilot wish to cruise at the fastest speed possible, he may advance the thrust levers to the MCRT setting and accept the resulting speed provided, of course, that it doesn’t exceed the maximum certified speed VMO/MMO. These are discussed in the chapter entitled “Speeds”.

Because maximum cruise thrust is not the basis for any performance level mandated by the aviation regulations , the data for MCRT doesn’t appear in the Flight Manual, but rather in the PEM and the QRH.

[Jet Transport Performance Methods, Blake et al, 1999]

[my emphasis]

There is quite a comprehensive explanation in the FCTM.