Assumed temperature reduced thrust

[JOE MAXY]

An answer i should know but here goes....

When we derate and then use an assumed temperature I've noticed that when T/O thrust is set it is not corresponding with the N1 reference bug(green carrot). Now i appreciate that when we assume we still have some extra thrust available and can set thrust to the n1 reference bug but my question is why when we assume does the computed N1 not match the N1 refernce bug on the N1 dial.

Thank you

[BOAC]

If it did, what would you push the lever to if you wanted full power?

[mutt]

I would have thought that the ref bug is N1 @ OAT, and the Computed N1 is @ the assumed temperature, so the 2 should be different.

Mutt

[747JJ]

That is exactly like BOAC and Mutt said on some types and companies. Some will set the reduced on FFRATS ( A "fancy 747" classic system). Should you need the full thrust available, FE would select GA and advance the Thrustlevers accordingly.
Again on some types the pilot will set FLEX or reduced thrust by selecting temperature and then selecting a detent on thrustlevers say Airbus and FLEX/MCT detent. Again TOGA thrust is available by just pushing thrustlevers forward.


The whole idea of reduced thrust or FLEX temperature or a fixed reduction in % of N1 or EPR like some manufacturers call it, is to save the engines. However full rated thrust is available and can be selected and any time.