737-600 Thrust Setting Question

[mirkoni]

If you look at the table of N1 setting for B 737-600, you can see that in one column (for the fixed pressure altitude) , as the OAT temperature rises from the lowest values, the N1 setting for max T/O gets higher and higher, which is logical.

But as you reach around around 100-102 Farenheit, the N1 setting starts to drop to achieve max T/O thrust, which is a kind of puzzle for me. Air gets hotter, density is lower, but you need less N1 to achieve full T/O thrust, then before at the lower temperatures?

Can somebody give a reasonable explanation, please.

Regards

[rudderrudderrat]

Hi Mirkoni,

With your example, the maximum available thrust falls off above 100 degs F because of things like the Max TGT limit is reached and Max turbine RPM speed at those temperatures.

[mirkoni]

OK let's take a concrete example.
For OAT of 140 F and pressure altitude of 2000 FT you have N1 = 88.9%

If I understand you well, you still have space to push thrust lever above this N1, and by doing that, you would cause EGT needle to enter a red zone?

Or other words, above some limit temperature, you deliberately have to decrease the maximum T/O thrust because of the EGT limitation?

[rudderrudderrat]

Hi,

Depending on engine wear - you might not be in the indicated "red zone". The engine manufacturer has decided that with a combination of RPM and TGT, the life of that engine will be compromised if you make it work even harder.