I have winds at 50 knots at my back, a very light airplane, and the autopilot is unable to climb at an acceptable rate, it keeps climbing at 100/200 fpm. I searched the issue tracking and did not find anything.

 

 

edit, I don't know what happened but I pressed lnav/vnav buttons again and it went back to normal. Strange.

 

David Frank

It will maintain a Knots Indicated Airspeed, not a ft/min.

It will do this with a constant engine thrust value (more or less) and using pitch to maintain speed. It will pitch up (climb faster) when it is faster than the speed requested by VNAV, and pitch down (climb slower/maybe even level off) if it needs to accelerate.

 

Things that may effect ability to climb are;

 

• The well documented FSinn (and maybe other weather generators that aren't ActiveSky Next) issue where the temperature becomes + instead of - at high altitudes (ie +55°C at FL370 instead of -55°C). With FSinn this always occurs at FL245. (24 thousand 5 hundred feet Mean Sea Level) and higher. This effectively changes "density altitude" - often to a point where wing lift and power output/pressure ratio is diminished so far as to not be able to climb.

 

• Another weather issue may be an unrealistic wind shift (common problem with the FSX default "Live Weather" feature) where the wind speed or direction changes hundreds of degrees and tens of knots in a second. Including (even commonly!) 180 degrees. 50 knot headwind turns into a 50 knot tail wind in 1/30th of a second (a single frame) and suddenly your aircraft lost 100knots. This will cause it to either stall, or at the very least suddenly pitch down/level off to try to regain the indicated airspeed as set by VNAV.

 

The other thing I see often enough is:

• "After takeoff checklist, Gear up!" being a thing.
  • Up to about 10,000ft the performance with the gear down is similar to gear up. (lots of excess climb available at 250 knots, and less drag at that speed.) After that, not so much...

Flap retraction schedule is also a thing, but this is less common a thing to miss, probably because of all the green flap numbers in the Speed indicator being a very obvious reminder.

 

There is of course an acceleration (of Knots indicated airspeed) at 10,000ft that will reduce the climb rate for about a minute as the speed increases from 250kts to 310+kts.

 

Finally, depending on how high this is occuring, you may just be too heavy (fuel weight + payload) to climb to that flight level. Ensure you entered the correct unit of weight into the FMC (Pounds are not Kilograms!)

 

There is 1 more issue that can be a systems/bug thing, but in that case you would also be talking about how the nose is pointing down while climbing. This is a very rare bug, but does happen. However, since you didn't mention the attitude/nose pitch being wrong in conjunction with the climb rate, I'll refrain from offering how to correct that problem you don't seem to have at this time.

It had no trouble maintaining speed, I had wind at my back, and was almost empty. My cruising alt was 390 so not heavy.

 

There are problems with wind and turbulence from active sky next I guess I will have to live with.

Trouble climbing more than 100ft/min at full thrust is a hidden "Trouble maintaining speed." It is unable to climb faster, because VNAV will not allow the speed to decrease from the target speed. In VNAV you should never see the aircraft climb and loose speed,

 

What altitude were you at when the issue happened? You mentioned FL390. Were you trying to climb TO 390? or were you trying to climb FROM FL390 to FL9999?

 

How much fuel did you have?

 

(remember, we can only go off what you say, so if you tell us you were at FL390, climbing to FL390, then... 0ft/min is appropriate  )

Ths is normal, the real thing does the same when tailwind increases during climb.

 

During climb you are in Vnav Speed mode.

So as said by Hopsik....you already have full climb thrust and the AP is maintaining speed by adjusting pitch attitude.

 

A certain amount of thrust is required to maintain your speed (to overcome drag).

Any thrust that is available on top of that, results in the climb.

This can be +2000ft/min at low altitude, but reduces as you get higher into thinner air to a few hundred ft/min.

 

It also reduces when an increasing tailwind during climb (20kt tailwind in 5000ft to 200kt tailwind in FL360) constantly reduces your indicated airspeed. You will hardly notice this loss of airspeed because the AP in Vnav Speed mode will constantly adjust (lower) its pitch attitude to regain even 1kt! But you WILL see a loss of vertical speed!

 

Once you get high enough Vnav Speed target changes from indicated airspeed to Mach.

At that point you will see slightly better climb performance again because as the AP is maintaining constant Mach you will see IAS reducing.

 

You can help Vnav climbing by using speed intervention and reducing the speed and/or Mach number. But it is not required. All other aircraft have the same problem....it is normal.

This could also potentially be the FSUIPC4.ini issue that's cleared by rebuilding the file. There's a weird bug where both the 777 and the NGX can lose their ability to climb due to some kind of corruption in that file.

I had Active Sky Next set to realistic mode, but that turned up wind turbulence and regular turbulence up too high. I moved them back to default and the fsx.cfg file turbulence effect to .5 and it's back to normal now.

Above FL280 I always switch to Vertical Speed mode for the rest of the climb to cut out the oscillations the VS goes through at higher altitudes. I gradually decrease the VS as the climb continues, always keeping it 800 ft/min or more. I started doing this because whenever my climb rate was less than 500 ft/min, the Radio Contact 4 controller would "remind" me what my assigned altitude is.

I had trouble last night coming into a turbulent and stormy descent to my destination. The AP was not keeping up speed properly even in flight change mode. I had to disconnect the ap and control the throttles manually so it wouldn't stall. The auto throttles refused to increase properly to keep speed. ASN turbulence doesnt work well with PMDG I guess.