Guys,Hope someone can help - I did post this a few weeks ago and unusually didn't get a single reply !! Maybe I'm dimmer than I thought and everyone else understands the issues. Anyway two things that still puzzle me which don't appear to be well covered in the FMC Manual or tutorials.1.What do I put in the OAT box - at the moment I guess at -50F for something like FL350 - are there any charts / graphs to give more info please ?2. What does the ISA Dev/QNH box do ? is it modelled ? The FMC Manual (page 73) just says that it is the 'Destination airport temperature deviation from standard.." So do you put in the destination temp or the difference between what (The departure airport or the OAT ) and the destination airport. What logic do you use if the dest temp is 10 degrees cooler, do you put in '10' or 'minus 10'?Dave

Dave,Sorry for missing your previous post on the same topic.1. You are basically correct. There are several meteorological sites where you can learn about OAT and even get real time data. www.noaa.gov comes to mind as a good starting point.In FS9 you need some kind of weather add-on to get a hold of the OAT. I am using ASV which will give me a detailed report about the current wind/temp on all my waypoints at all common flight levels.2. This value will, according to B. Bulfer, have a minimal inpact on the descent forecast. ISA temp is 15

I note that on one of the temp input pages where it displays both F and C, if I follow the numeric (i.e. -40C) for cruise level (ASVe winds aloft report) in the scratchpad and then LSK it, it displays -40F/-40C.Anyone else experiencing this? I also tried /-40C in the pad but as I recall it did not accept this.

So what is wrong Ron?-40

Forgot about that specific value being the same :). Coincidence that was the value for my first few runs with it.