View Full Version : FLEX vs Target N1 on T/O performance data
We've always used FLEX temp for setting T/O thrust with no info re the target N1.
Does anyboy's performance data include N1 along with the FLEX temp? Seems to me that if N1 is to be monitored during the roll, shouldn't there first be some kind of insight into whether the FADEC number displayed is realistic or not, otherwise what's the point?
The problem is calculating the Flex N1, what you are looking at is a guage N1 and not the actual engine N1, because of the tempertature difference between ambient and flex, you cannot just look at the higher temperature and take the N1 value. We have therefore never expected crews to calculate the Flex/Assumed N1.
Mutt
crjlover
25th Feb 2009, 19:38
On the E195 manuals there are tables to corect the N1 to N1 flex, but I don't know if our crews use to calculate it or not.
Denti
25th Feb 2009, 19:46
Not the bus but the performance software for our 737s allways gives the target N1 for whatever combination of reduction we used (derate only, assumed temperature only, both combined). This can be crosschecked as the FMC gives the target N1 as well and of course later on can be checked on the engine instrumentation during the take off run.
FE Hoppy
25th Feb 2009, 23:35
On the E195 manuals there are tables to corect the N1 to N1 flex, but I don't know if our crews use to calculate it or not.
We certainly teach crews how to do it but what the airlines do after their pilots leave here varies considerably. In reality all the crew is doing by manually calculating the Reduced N1 is confirming they put the correct TO and FLEX temps in the box. The box won't get it wrong so if there is a difference it's down to miscalculation by the crew or finger trouble.
Denti
26th Feb 2009, 08:55
The box won't get it wrong so
That is, sadly, not allways true. We had the case where the box (FMC) did it correctly initially and upon line up changed the target N1 values considerably, to a much lower value. Nothing happened as the P1 in question noticed it during the acceleration and manually overrided the autothrottles to max take off power, but if the take off would have been continued at the box computed values it would have ended in a high speed overrun. The box was replaced and found faulty lateron.
We used to have the tables for the reduced N1 computation on our checklist and had to use it to crosscheck the FMC on the first flight of a day, but that was discontinued after a few years of operation and the tables were removed.