738WL does not want to rotate if being empty

[Cristi_Neagu 134]

The weather program is not an issue here. He said he got the plane to 150kts. It doesn't matter if the OAT is -15C or 50C. If you get to 150kts, you will lift off. The major impact temperature has is on engine performance. In high temperatures, the engines don't develop that much power. It will take longer to get to Vr, but when you get there, you can lift off. My guess is that the CG is out of limits. You might be seeing 25% CG on the takeoff page, but what does the load page say (you know... MENU->FS Options). That may be way off 25%, but the takeoff page only goes to 25%.

[vonmar 123]

I wonder if the tutor flight is ok?

[aentwis 61]

You ask me, this is a density altitude issue... the airport is at 5000', and only 1844m = 6050' of real estate to get off the ground... and increases in temperature are going to make things worse... Increased density altitude = lower performance... you may need double the amount of runway to get the aircraft off the ground... Andrew

[Chrisv007 0]

I had the same problem but in my case, the yoke had stopped working (the panel freeze issue I guess). The plane would simply roll off the end of the runway at takeoff speed.

[FlyingAxx 2]

Could you elaborate what a pure manual attempt means?

I've meant pure manual throttle handling in the range above 96% and as well a manual trim setting "somewhere" in the beginning green range above 3.nn - just flying in "Piper Cub mode" as Captain Dave uses to write in his blog http://flightlevel390.blogspot.com/. At the moment I'm tracking a mistake I did when using the TOGA button and I think I got it this early morning before starting to work. It seems that I did not sufficiently applied thrust when going over the threshold of 84 knots. I recognized a slightly decreasing N1 during t/o but I'm wondering however, why the plane does not take off even if being beyond the calculated speeds. Obviously there was no problem when I applied full throttle after pushing the button. I think I did not recognise it before because of those long runways I used in my previous flights. I'm still not sure what is going to happen. Even if I would lose severe thrust because of a lever setting of (e.g.) 50% only after reaching 84 knots, the plane should rotate around the calculated speeds after pulling in the levers to a sufficient level. It did not react at all to the yoke movement. There might be an issue, but I'm not really sure.

I wonder if the tutor flight is ok?

Yes it worked fine (more than once).

You ask me, this is a density altitude issue... the airport is at 5000', and only 1844m = 6050' of real estate to get off the ground... and increases in temperature are going to make things worse... Increased density altitude = lower performance... you may need double the amount of runway to get the aircraft off the ground... Andrew

That's why I checked the "books" and there was no doubt for me that it should work. A last word regarding ASE or other weather phenomena: I could reproduce the behaviour even with clear skies (no weather)....will start testing now again... but first I need a

[kevinh 409]

You ask me, this is a density altitude issue... the airport is at 5000', and only 1844m = 6050' of real estate to get off the ground... and increases in temperature are going to make things worse... Increased density altitude = lower performance... you may need double the amount of runway to get the aircraft off the ground... Andrew

The calculated V speeds should allow for density altitude, giving you higher speeds. Axel got to 150 knots in the distance available so there's enough runway. I haven't got any Andean runways at 4999 ft, so I replicated this takeoff at Nairobi, which is a little higher (5340 ft IIRC). I used the same ZFW, fuel weight, QNH and TAT. The FMC calculated the same CG, trim setting and V speeds as for Axel. Unlike him I was able to rotate and take off without any problems. So the NGX is certainly capable of this takeoff. I don't think it's a weather model issue as his problem happened while still on the runway, so temperatures and pressures haven't changed. Forgetting to set takeoff flap might explain it. I've done that a couple of times and not had any warning of it during the takeoff roll to alert me. Kevin Hall Edit, forget the takeoff flap setting, it doesn't make much difference to the NGX. Just tried it again with flaps up and still managed to rotate and lift off to achieve V2. TO warning horn worked just fine too! So I haven't any new suggestions, only to confirm it should work (and does on my NGX).

[FlyingAxx 2]

Ok guys, it's like blowing hot and cold it seems... I just made some attempts under "controlled" conditions, by using all the time the same saved flight. I always where capable to lift off - even then when waiting to correct the wrong thrust lever setting quite long.

The calculated V speeds should allow for density altitude, giving you higher speeds. Axel got to 150 knots in the distance available so there's enough runway. I haven't got any Andean runways at 4999 ft, so I replicated this takeoff at Nairobi, which is a little higher (5340 ft IIRC). I used the same ZFW, fuel weight, QNH and TAT. The FMC calculated the same CG, trim setting and V speeds as for Axel. Unlike him I was able to rotate and take off without any problems. So the NGX is certainly capable of this takeoff. I don't think it's a weather model issue as his problem happened while still on the runway, so temperatures and pressures haven't changed. Forgetting to set takeoff flap might explain it. I've done that a couple of times and not had any warning of it during the takeoff roll to alert me. Kevin Hall Edit, forget the takeoff flap setting, it doesn't make much difference to the NGX. Just tried it again with flaps up and still managed to rotate and lift off to achieve V2. TO warning horn worked just fine too! So I haven't any new suggestions, only to confirm it should work (and does on my NGX).

It seems to be related to a specific (wrong) thrust lever setting. In such cases it even does not help to push it forward to the block. However, I never did as many take-offs in a row as far as I can remember. The training effect is obviously that I cannot surely reproduce the behaviour as it seemed to be the case when I decided to post it. ASE dosn't looks like to be the trigger as well. In a row with different thrust lever settings (while under TOGA regime and more or less late reaction on a decreasing N1) I experienced two looooong runway runs into the wild (unfortunately the airport sits in a hole) with speeds well over 150 knots - one with ASE and one without. Probably someone else can reproduce the habit, however, I've learnt not to forget to throw the throttles forward. Thanks for all who responded (I'm going to fly now). EDIT: Kevin, flaps setting was 15° and not forgotten! The speed bug showed 126 knots being the time to rotate.