# T/C OAT/PERF INIT

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Hi,I wanted to asked, in the PERF INIT page of the FMC,the (T/C OAT) where can I find it to enter?Thank you very muchFriendlyPaul

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If you have ActiveSky or FSMeteo, you should be able to get the air temperature and wind speeds aloft direct from the program (see your user manual for details).If not, you can estimate by assuming a 2C (3.5F) degree drop for every 1000' of altitude (up to about 50,000 feet or so). These figures are for a standard day 15C/59F at sea level and 29.92 inHg. In the wintertime, however, the falloff seems to be more gradual - about 1C for every 1000'. In summer, it's more rapid - close to 2.5 or 3C for every 1000'. As a general rule of thumb, it's usually about -30 to -35C at 30,000.You can also interpolate between the temperature at 50,000 - where it's usually a fairly constant -56C (-70F) regardless of time of year - and the temperature at the surface. So if it's 5C at an airport, at 2000 MSL. You could do a little algebra to figure it out:y = mx + bor:temp = m (altitude AGL) + surface_tempm = (change in temperature) / (change in altitude) = (-56C - 5C) / (50,000' - 2,000') = -1.27 x 10^-3 or ~1.27 degrees for every 1000 feet above the surface you climb.so for your 2000' foot airport, the temp at 35,000 MSL (33,000 AGL) would be calculated as:temp = -1.27 x 10^-3(33,000) + 5 = -42CObviously, temperuture falloff in real life is not perfectly linear (especially near the surface where you can get temperature inversions), but it's close enough for estimation purposes. You should be able to get wind speed aloft right out of the advanced weather dialog in FS.Cheers,J

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Thank you very much sir.Good fliesFrinedlyPaul

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