Ok, I know "how" to "set" a temperature or 1/2 in the FMC, but how do I know which one to use? Is there some standard convention to go by?I read the manual and all I could get was the circumstances in which I could NOT use a derate.All I know is that if the runway is about 10,000 feet long, use 54 degrees... any thing else and it is all blind, using either no derate or D/1 or D/2 takeoffs.So some insight on what these numbers mean and which ones to use would be much appreciated!

The temperature depends on a number of things including:Runway lengthAirfield elevationAmbient TemperatureAircraft WeightTakeoff configuration (eg. Flap setting)Basically what it's for is setting a de-rate specific to the conditions for that particular takeoff. Simply put, it's a temperature that will limit the thrust of the engine to a point that is just enough to get the aircraft airborne by a certain point on the runway.ex. Runway length is 10,000ft. You want a 'margin' (amount of runway remaining at lift off) of 2000ft. You can set the engine to give you enough thrust to get you to your VR in 8000ft.I actually use a freeware program called TOPCAT for every B744 flight. http://topcat.ofplan.net/It hasn't been updated in a long while but it's still usable. It will provide several temperatures to choose from giving you different margin's. You can also choose items like what flap setting you'll use, whether you will use anti-ice, and how many packs, if any, you intend to use on takeoff. You will also have flap speeds for both climb out and approach as well as auto-brake stopping distances for landing.There isn't any support for the program. (Don't bother with the forum. It doesn't contain anything related to aviation and anything appropriate for under 18 years old.) There is a manual available but I just learned to use it the same way I usually learn things; see what all the buttons do. (Unless something goes really wrong, then I turn to the manual.) I'd be happy to help with anything I can.As far as I can tell, the site's abandoned. Sad really, this would be so useful on so many other aircraft. Maybe PMDG could include a takeoff calculator like this with future aircraft?Ryan GamurotLucky to live Hawai'ihttp://www.virtualpilots.org/signatures/vpa296.png

>Ok, I know "how" to "set" a temperature or 1/2 in the FMC,>but how do I know which one to use? IsSearch this forum for "derate". This topic has been covered extensively.Michael J.http://img142.imageshack.us/img142/9320/apollo17vf7.jpg