B744-F takeoff performance page doesn't take negative temps

[Guest balt]

as per the subject. trying to enter -4 into the temperature field but it wouldn't take it. any ideas anyone?- balt

[downscc 1,327]

Try the -/+ key on the FMC keypad instead of entering the sign symbol from the computer keyboard, that's how it must be done on the 737NG and I assume the FMCs have some similarity.

[Mats_J 2]

Balt,What temperature field are you refering to?Cheers,

[Guest balt]

yup, i always and only use the mouse to click the keys on the FMC, and I was trying to enter -4

[cowpatz 243]

That is not for confirming OAT but for entering the assumed temperature derate temp.

[Mats_J 2]

To add to Steve's clarification:The assumed temperature range goes from (I think) 30

[Guest BAW1085]

As I understand it the derate temperature selection is basically ignored unless you specifically want to derate the takeoff. Never heard of confirming the OAT ? The Engine control units know the temperature and ambient pressure and will give max thrust accordingly. The derate function is simply one of fooling the ECU into thinking it has less power available than it actually does by manipulating the temperature. Entering a higher temperature simply limits the engine thrust. The process of derating can be summed up as a method of calculating exactly how little thrust the engines can provide in order to get you safely airborne in a legal manner. Obvioulsy less thrust equals less wear and tear and less fuel burned.I would like to add the way that PMDG have modelled this feature is spot on. It seems very accurate when compared to published data. Using the derate function accurately and consistantly provides another level of sophistication to the Queen which I find fascinating. Once you've calculated the derates try to testing the V1 stopping distances. A high derate and high TOW puts you right on the edge of the stopping performance envelope. Having tested a wide variety of derates and V1 stopping distances I can attest that the PMDG modelling is again spot on. Check the SOPS on how to conduct a high speed abort and try it yourself.I think the lowest derate is actually 16