While looking throught some of the aircraft.cfg files, I found the following entry:[GeneralEngineData]max_contrail_temperature = -30 //Temperature (deg C) below which contrails may appearI could not find the same entry in the default 747 or 777 included with FS2004/COF/FS9. So I wrote to MS support and received a reply that did not say much:"As I understand, we are Unable to find max_contrail_temperature in aircraft.cfg files for the three default Boeing jets (737, 747, and 777.Bob, max_contrail_temperature entry is found only in Boeing jet 737 and it will not be present in other aircrafts, this is by design. These entries will not effect the display of the contrails.I hope this information helps."Not a very informative reply from Microsoft. Has anyone else tested this entry to see what it does to the aircraft? Is it really an entry taht will not effect the display of contrails?ThanksBob

I just played with this entry in the default B737-400 and changed the value to 30 (30 degrees C = 86 degrees F) and took off from KSEA. I had contrails from the start of my takeoff roll up to altitude.Original entry:max_contrail_temperature = -30 //Temperature (deg C) below which contrails may appearModified entry:max_contrail_temperature = 30 //Temperature (deg C) below which contrails may appear