I was wondering how do you choose what flex temp to use when aircraft is not fully loaded. Is there some sort of chart to determine it or does it involve some complicated maths? I know that Boeings have derated thrust options in FMC but Airbus and MD11 doesn't, you have to enter flex temp. So how do you decide what should it be?Greg

I was wondering how do you choose what flex temp to use when aircraft is not fully loaded. Is there some sort of chart to determine it or does it involve some complicated maths? I know that Boeings have derated thrust options in FMC but Airbus and MD11 doesn't, you have to enter flex temp. So how do you decide what should it be?

Are you asking how it is done in general terms, or specifically for the MD-11?For the MD-11 try these charts: http://library.avsim.net/download.php?DLID=137469There is also a payware tool that works with a range of aircraft: http://www.topcatsim.com/ (trial version available)In the real world I believe pilots have tables (or software) specific to the actual runway in use for takeoff, but the general principle should be similar to what you see in the tables and the tool mentioned above.

Sorry, I mean in real life. Greg

The above poster already explained, These days company's provide there crew with a onboard laptop that has software loaded. I've had a look at the FEDEX software for the MD11 (APLC airport performance laptop computer)and it looks and behaves pretty much the same as the TOPCAT software you can purchase in the link above. In the event that you dont have the laptop for whatever reason it's back runway charts and a calculator.Rob

On the 737s I've flown, you have two options - use the book, or just ACARS your request preferences if any - flaps, derate, reduced thrust, contaminated rwy, etc.With the ACARS request, you just get a message that either fills in the data for you on the PERF pages, or you punch it in yourself - depending on how much money the company wants to spend. With the book method, you find the airport and then the runway. There you choose a configuration (flaps/bleeds). On the table, you find the Actual ambient temperature. That tells you your MTOW. Now, if you weigh less than that you can reduce/derate.Let's say you're taking off on RWY 32 at PANC and the plane weighs 132,000 pounds and the TEMP is 15C. If you look at the chart, it says with an outside temp of 15C, you can take off at 144,000. We're under that, so we can reduce. So, looking at the same chart, you scroll down the MTOW column until you find where your actual wt (132,000) is the MTOW for a certain temperature. Let's say it comes out to be 39C. So, at 39C the chart says the most you can take off with is 132,000. Punch 39C into the FMC, et voila!