B737 NG Certified/Rated/Derated thrust
Hello folks, the company I work for recently began using double derates, so a fixed soft derate and assumed temperature together. This has led to some confusion in certain cases as you might imagine.
Colleagues have told me that they prefer not to derate because 'in windshear and go-around you will not get maximum thrust anymore'. The manuals aren't terribly clear on this, I checked the AMM-SDS as well but couldn't find a clear statement concerning this. Here is my understanding of the thrust ratings (Please correct me!)
Firstly the CFM-567B has a maximum certified thrust of 27.3Klbf - well, if N1 and N2 stay below redline - can any rated engine achieve this thrust when fire-walling the thrust levers? AMM SDS 73-21-00 mentions six N1 reference speeds, one of them is Maximum takeoff/go-around at 78°TRA (which I assume is based on engine rating) and also mentions maximum certified thrust at 82.5°TRA. Would that be 27.3K?
The identification plug will determine the hard derate (so the maximum thrust the EEC will provide voluntarily) and thus the maximum thrust available on the FMS at TO. Also this will dictate the thrust available when double clicking TO/GA.
The FMC will allow selection of a fixed/soft derate and an assumed temperature. Depending on the pins set the thrust limit displayed might be either only the TO/TO-1/TO-2 fixed derate thrust or the double derated derate+TASS thrust. Am I right in my understanding that this will not limit you on subsequent go-arounds or during windshear recovery (but instead the maximum rated thrust set by the ID-plug)?
What a mess... thanks in advance for your input!