Hi CaptainsI've come up against a question that the manual doesn't seem to cover:On the FMC (737 800/900 series), when setting the flight up, I eventually arrive at the 'N1 LIMIT' page. Top left LSK is 'SEL/OAT' with an input area of 4 dash lines and a temperature (i.e. ----/15).Firstly, what exactly is being requested by 'SEL/OAT'?Secondly, what input format will the dash-lines accept?Finally, is there a relevance to this field (i.e. does it make any difference to settings/performance etc.)?Thanks for any help.Toni.

SEL = selected temperatureOAT = sensed ext temperatureManual section 8 page 37.Have a nice readingBRClaudio

Thanks ClaudioI hadn't read that far into the Manual....:-roll Still a bit confusing though - the Manual says 1 or 2 digit inputs upto 99 are acceptable, but anything less than sensed OAT (default 15 degrees C.) result in 'invalid input'.Thanks for pointing me in the right direction!RegardsToni.

Toni,16-70 degrees are valid inputs. Though the lower values are seldom used.Regards,

And like Toni asked in his original question, will this have any affect on the settings/performance?Cheers,

YesThe higher value of your selected temperature the lower the value of your engine max %N1. This is used if you know you are light and have enough runway to spare.This will decrease thrust down to 75% of rated thrust. This SEL TEMP thrust reduction is used more often than TO-1/2 and CLB-1/2 derates because SEL TEMP thrust reductions are not seen as a hard reductions. If you need more power you are free to use it in a SEL TEMP TO or CLB. While as in the DERATE the extra thrust is not availible to the pilot.Read more about it here:http://www.b737.org.uk/assumedtemp.htmHope it helps,

>And like Toni asked in his original question, will this have>any affect on the settings/performance?Quote from manual section 8 page 37"The SEL entry is used to enter a temperature that is different from that being detected by the air data computer. For example if a temperature difference is expected between the current aircraft location on the airfield and the temperature that is expected at the runway threshold, the expected temperature can be added so as to ensure that an accurate estimate of thurst ratings can be computed by the FMS."BRClaudio

OK, and if I don't enter anything there myself the OAT will be used instead?

Thanks, just read it and also the information Mats provided in his link. Guess there is always something new to learn ;-)

Yes that's correct!If leave SEL out it will use OAT. Meaning you will have full rated thrust.Cheers,

OK, thanks Mats!

All very interesting.Thanks everyone.Toni.

Yes, I had always wondered about that one as well.....Tks guys...And good Question....Tony P.