Can't get airborne - is it the weather?

[RaptyrOne 1,409]

Hi all, really hoping for an answe to a frustrating problem. I have many incident free flights in the 744X but recently I keep hitting the same problem. Getting the acft to move requires a higher throttle setting than I usually experience but when I get to the take off roll using TOGA the acft accelerates at such a leisurely pace even thoiugh engines are spooliong right up as normal. V1 is never reached at a safe point and if I do try to get airborne, even at the rotate call the acft goes into a stall and refuses to fly. I noticed the OAT was at 120 C at obe stage and by resetting this by going into wether settings I got it fixed but now it happens even at 10 C. Acft is not overweight.Is there a known bug or a known workaround for this? I stress that I am not a newbie on this acft - FMS is set correctly, take off speeds are set etc. Acft just won't fly like it used to. Reducing the weight to unrealistic light load does sort the problem out but that's not a fix. Look fwd to any guidance. Tx in advance

[lbarber 20]

Sounds like some kind of throttle rollback issue, maybe your joystick/throttle is overriding TOGA when the AT commands THR HOLD at 80 kts (this can be turned off in the PMDG settings if it is indeed the problem). Have you checked the N1/EPR after 80kts?-Lee Barberhttp://home.nc.rr.com/uniuniunium/dvasig.jpg

[RaptyrOne 1,409]

Thanks Lee, but it's not that. Problem seems related to FSX weather at airports with a higher altitude. All engine indications are perfect but the acft is massively sluggish. Also wondering if FSUIPC may be an issue (I need it to make my yoke/pedals work properly with key assignments).In fact it seems even the FSX acft struggle with this problem so it is not a PMDG acft issue as such but this is the only acft I fly hence me being here.CheersGreg

[NoahBryant 26]

Maybe a stupid question, but what is your weight figures for fuel/payload?

[Guest Peter Lloyd]

GregWhere do you have the trim set?Guess you are not trying to take off at 6,000ft amsl at midday.Hang in there, there is a simple solution someplace!Peter

[craig_read 43]

I think we need some more information here to make a diagnosis, the information, perhaps suppy us with the following..1 - Aircraft Weight/Payload/Fuel details (MTOW?)2 - Your chosen flap setting (10 or 20?)3 - Thrust de-rate? Is there one?4 - Trim setting (FMC value on the Takeoff page and in manuals)5 - Airfield elevation6 - Air temperature, pressure7 - Runway length?Sometimes at higher weights a lot of new simmers find the 747-400 a difficult aircraft to get airborne, at maxiumum take off weight it can be very tricky indeed.. The 747-400 at MTOW can weight in at over 850,000lbs, that's extremely heavy, and requires a lot of power and initial roll speed.. For a weight like that I'd be using flaps 20, no de-rate at all, and ensuring I have the longest runway available to me.. I'd ideally prefer take off permission while rolling past the rwy hold line so I can get a bit of a rolling start too, it certainly helps having the extra 5 - 10 roll just before you line up then apply take off power.. But at these weights the aircraft will be sluggish..Let us know..Craig

[RaptyrOne 1,409]

Only happening where airfield elevation is higher. FAJS is at 5500 feet.To answer your Q's Craig:1 - Usually close to but NOT over MTOW. I like to fly real time 12 hour continent hops. I set up in the load configurator program before I start FSX2 - Most often 10 for takeoff, but also struggle with 203 - Because of the problem, avoid setting a derated thrust for t/off.4 - Trim is set as per the FMC - usually in the region 5-65 - Elevation high - 5500 feet. I do not have the problem at sea level or with a near empty acft.6 - Usually around 14 degrees but FSX has been known to up this mysteriously to around 70 - 80 celcius as reported in the FMS and EICAS (talk about global warming). I suspect that sometimes when I correct this, it does not fix it. The acft would perform badly at that temp, assuming anyone could survive it!7 - FAJS runways are 14500 feet and 11150 feet. Usually DRY. I don't always fly with ATC as it irritates but do where possible depart into wind also - anything from 5-10kts.I really think it is more FSX and / or FSUIPC behaving badly than the acft itself.

[Guest piper99]

I have you check the takeoff runway limit weight charts (in the takeoff section of the manual)?Depending on airport elevation and ambiant temperature, the maximum takeoff weight might be reduced.Christophe

[downscc 1,327]

Elevation is a definite factor in reducing MTOW.. the reason KDEN added a 15,000 ft runway recently was to allow the launch of Asian traffic. Your density altitue is the real key, which goes high quickly in warm humid air.Christophe hit the nail on the head.. gotta use the takeoff performance charts in the AOM (same as real world). Also, many like a program called TOPCAT that I intend to become familiar with someday, that calculates the takeoff data for you.

[stevenp 1]

I recently did a flight from Denver off one of the 10,000ft runways at 800,000lbs. with a derate dt-5% and it did fine for me. Flaps 20, I don't remember trim, but the only problem I had was that the initial climb sucked- it was slow. OAT was 15

[rocketfs 2]

For runway elevation, count 2% IAS for every 1000' extra.ex: for 5500' your ground speed will need to be 11% higher for the same IAS as at sea level.Best Regards,Bert Van Bulck

[Guest captnmel66]

I'm a real world pilot and we dont take off on ground speed but IAS. this whole thread is about density altitude, Hot, High and heavy dont mix. If you were to take off and lose an engine out of Denver you would make the news. I have flown in and out of Denver in a few different corporate jets that I fly and I will say the tires do sing a different song because of the speed they hit during the longer take off runs. Just my two cents worthI will say these PMDG add ons are some of the bestJust winging it!