Thanks a lot for your replies and the patience to answer these basic questions,
Here is a rundown of how we do..
(figures are arbitrary as I do not have docs at hand)
given: Actual G.W.:71t / OAT 18°C / airco on
1-We have the option of fixed derate from 26k to 24k. So, usually we start on the 24k t.o. analysis page.
2-First look at the OAT and determine MTOW and if we are climb or field limited. So far I haven't seen any other of the 5 limitations in our operations. In this example I will use climb limited.
3-Then determine 'airco on' penalty + climb limited, usually 2000 kgs
4-71t+2t=73t will give us the assumed temp. Let's say 32°C
5-Then check V speeds consistend with actual weight: V1=143 Vr=146 V2=152. Crosscheck with FMC calculated speeds and confirm.
Given this scenario, we only know that we are climb limited but we do not know our ASDR for example except that it is less then ASDA of course.
We do not 'play'with distances to add to ASDA. We do however, reduce weight only if the standard rate of 26k will not give use the required performance.
My reason for the questions are the 'what if'scenarios; what if we have to abort at V1, what if we go n-1 at V1 and continue etc..Just like to know what i'm doing and more important, what the aircraft can and will do.
Thanks!