did you guys notice a difference in the calculated trim on the fmc and with the green band on the trim wheel?i tried flying out of there just now, and a few other of those recently, and noticed that the calculated trim value is very low compared to what the green band indicates. it generally is right at the very top edge. the first time i left it, and had similar problems where i had to trim back while pulling back on the yoke to rotate.since then i just put the trim into the middle of the green band and i can rotate and take off correctly.i don't know why the value in the FMC differs from what the band indicates, or if that's how it's supposed to work or what. at slsu the fmc suggests 3.01 but centered is 5.32 and with the centered value it rotates easilycheers-andy crosby

Was your takeoff trim actually 3.56? I've never seen a trim this low. In fact, I've been playing around with cold weather operations. During de-ice you set full nose down trim (for de-ice only, then reset takeoff trim) and I see 3.95 as my maximum nose down trim. I wonder if this could have been an issue.

There's going to be lots of cabin altitude warning horns going off !!

did you guys notice a difference in the calculated trim on the fmc and with the green band on the trim wheel?i tried flying out of there just now, and a few other of those recently, and noticed that the calculated trim value is very low compared to what the green band indicates. it generally is right at the very top edge. the first time i left it, and had similar problems where i had to trim back while pulling back on the yoke to rotate.since then i just put the trim into the middle of the green band and i can rotate and take off correctly.i don't know why the value in the FMC differs from what the band indicates, or if that's how it's supposed to work or what. at slsu the fmc suggests 3.01 but centered is 5.32 and with the centered value it rotates easilycheers-andy crosby

That's exactly what I think. When setting the trim into the middle there is no problem to take-off. Setting it to the low upper edge causes the plane to remain on the runway. The calculated value is just at the upper edge of the green band.

Was your takeoff trim actually 3.56? I've never seen a trim this low. In fact, I've been playing around with cold weather operations. During de-ice you set full nose down trim (for de-ice only, then reset takeoff trim) and I see 3.95 as my maximum nose down trim. I wonder if this could have been an issue.

Yes, this was the calculated value. The picture just freezes the situation after the plane left the runway when I already had changed the trim setting in order to rotate.

Don't forget, you also have a "bump" setting for additional thrust. You'll need at it high altitude.

That´s only partially true. A 600 with only about 9k lbs of fuel and no payload or pax will probably be able to use assumed temperature and/or derate depending on rwy extension even at high density altitudes. I say probably because I do not have the charts or topcat (which is based on Boeing figues) to back me up on this at this moment. But I find it highly unlikely that it would not be able to. Unless of course we´re talking about taking off from a 2500 ft rwy in La Paz on a bright hot summer day with high local pressure.

That is what the term "high density altitude" is all about. It is very unlikely that assumed temp or derate will be used for any commercial operations of a jet of this size out of any airport at such high altitudes, particularly if density altitude is high... check out the term "density altitude", I am not talking above MSL or pressure altitude here...And the chances are that a lower flap setting will be used for hot and high...Andrew

My trim was about 4.0, witch seemed about right with the aft CG(23.4%). What was your CG? If it is aft and the fmc gives you a very light trim setting, somethings wrong. You may have to uninstall, delete, and go with a clean install. Most of high altitude places that I've flown through real world also came with high climb gradients. We would also take as much gas as we can to make it back to the states. In those situations, i have never derated in the heavies or biz jets that i've flown through out South America.

Can you take off normally with the same settings from a sea level airport?

That is what the term "high density altitude" is all about. It is very unlikely that assumed temp or derate will be used for any commercial operations of a jet of this size out of any airport at such high altitudes, particularly if density altitude is high... check out the term "density altitude", I am not talking above MSL or pressure altitude here...And the chances are that a lower flap setting will be used for hot and high...Andrew

I´m aware of the meaning of density altitude Andrew, I was referring to high-altitude rwys, not particularly high density-altitude scenarios. Hope this clears it up.

Can you take off normally with the same settings from a sea level airport?

Just tried it in Hamburg (EDDH) and got the same problems. OAT had been 15°C, 1/3 fuel, 0 payload. V2 = 122, flaps 15°, CG 22.8%, trim 3.56. It accelerated along the runway like made but did not rotate even when pulling the yoke full. Far in the red band at about 200kn (even above a bit) she jumped into the sky (I did not use the trim this time).Second try, just a random load of about 30%, flaps 5°, trim 4.54 and no problem at all.What's the reason for an behaviour like that?

Was your takeoff trim actually 3.56? I've never seen a trim this low. In fact, I've been playing around with cold weather operations. During de-ice you set full nose down trim (for de-ice only, then reset takeoff trim) and I see 3.95 as my maximum nose down trim. I wonder if this could have been an issue.

You can trim lower if you select a higher flap setting.Bert Van Bulck

Just tried it in Hamburg (EDDH) and got the same problems. OAT had been 15°C, 1/3 fuel, 0 payload. V2 = 122, flaps 15°, CG 22.8%, trim 3.56. It accelerated along the runway like made but did not rotate even when pulling the yoke full. Far in the red band at about 200kn (even above a bit) she jumped into the sky (I did not use the trim this time).Second try, just a random load of about 30%, flaps 5°, trim 4.54 and no problem at all.What's the reason for an behaviour like that?

I did Touch and Goess today, with a weight of about 52 tons. The C.G. indication if the FMC was about 3.7 (flaps 25). I set it to that value. No problem on takeoff. Trim correctly set, no additional trimming required during climb.Bert Van Bulck

Hello again Axel:I am not knowledgeable enough to try and determine what technical issues might be creating your problem, however, I have found that trying to find “what it is not” by a process of elimination, might guide you to the problem and hopefully the solution.Some questions you might want to ask yourself are:Do you have a similar problem at low altitude airports?Does it happen in all versions/models of the NGX?Did you try to take off without setting TOGA, but manually setting full power (you might red line the engines)?Have you tried a mid-altitude airport such as KDEN (has nice 16,000 ft runways to try!)?Have you tried taking off with only one of your restrictions and not both (high and short)?Do you have any other add-ons to try (or default aircraft) to see how they behave under the same conditions?Maybe some of the answers to these (and any other questions) might reveal something you are missing.Good luckRobertoPS 1: Are you sure that pounds are pounds and not kilograms and gallons are gallons and not liters?? PS 2: Try the Latin VFR scenery for SLSU (It is payware and I don't get a commission for this plug :-) ). It has the "hump" in the middle of the runway just as the real one does. So if you take off on RWY 05, and you keep a V/S of "zero" after rotation, the runway just "falls off". Great to try in a C-182!

Hello again Axel:I am not knowledgeable enough to try and determine what technical issues might be creating your problem, however, I have found that trying to find “what it is not” by a process of elimination, might guide you to the problem and hopefully the solution.Some questions you might want to ask yourself are:Do you have a similar problem at low altitude airports?Does it happen in all versions/models of the NGX?Did you try to take off without setting TOGA, but manually setting full power (you might red line the engines)?Have you tried a mid-altitude airport such as KDEN (has nice 16,000 ft runways to try!)?Have you tried taking off with only one of your restrictions and not both (high and short)?Do you have any other add-ons to try (or default aircraft) to see how they behave under the same conditions?Maybe some of the answers to these (and any other questions) might reveal something you are missing.Good luckRobertoPS 1: Are you sure that pounds are pounds and not kilograms and gallons are gallons and not liters?? PS 2: Try the Latin VFR scenery for SLSU (It is payware and I don't get a commission for this plug :-) ). It has the "hump" in the middle of the runway just as the real one does. So if you take off on RWY 05, and you keep a V/S of "zero" after rotation, the runway just "falls off". Great to try in a C-182!

Thanks for your hints Roberto, today I prepared a testing list a bit similar to yours but it really takes time to go through it - specifically if you want to change the aircraft.The first question can be answered with "yes", it happens at low altitudes, too.2nd: Yes, but I did not try all typesYour PS : Simple to answer as 1/3 of fuel remains the same and zero payload as well regardless the units... BTW, 25% of payload required a bit higher trim setting as calculated, 30% and higher caused no problem at all. And now I have to go to bed - it's late and I'm expecting a "hot day" tomorrow.

I suggest you try to recalibrate your joystick. I have just tried your SLSU take off, -600, 1/3 fuel, 0 payload, Trim 3.57 I rotated normally at Vr (122)though I had to use the full range of motion of my joystick. Alternately, you could just use flaps 10 - same Vr, less drag, better CoG.

Might be a help for sharpening our high alt. take off knowledge :http://www.smartcockpit.com/pdf/plane/boeing/B737/misc/0002/