Bleed Demand, EEC's and 737NG's

[QAVION]

Thought I'd posted this one last night, but I think it got lost in the wash....

In the Boeing 737NG Maintenance Manual, it is written that the rpms (N2's) are increased to allow for bleed system demands, but also written elsewhere in the manual that the N1 speeds are reduced because of bleed system demands (Note here that it specifically says "speeds" rather than limits). Not having done a Basic Gas Turbines Engineer's course, my first inclination would be to say that if you increase N2, the N1 would would increase (and possibly vice-versa)...Can the EEC manage the airflow and fuel flow in the engine to allow for the independent operation of N1 and N2 (within a certain range) to compensate for bleed demands... or is the BMM talking about different ends of the power band here (idle vs the rest)... and the two controlling systems never interfere with each other?

Thanks for any input.

Regards.
Q.

[B73567AMT]

There is no independent control for each LP & HP compressors by the EECs. But extracting air from the high-pressure compressor for aircraft bleed demands may slow the compressors a bit.
EECs will compensate for these bleed air demands by allowing more fuel. Adding more fuel will increase total engine thrust...meaning both spools will increase in speed.
Keep in mind however, that the none of this may be seen in the flightdeck. FADEC engines allow for small changes in N1 without any indications of these changes eitehr on the N1 indicators or the thrust lever movement.

Hope this answered your question.

B73567AMT

[QAVION]

Thanks B73567AMT.

You may have just provided the clue I was looking for...

Cheers!
Q.