Hi,
Departed VTSP with almost max weight. Performace was okay and in limits. After takeoff climb was slow which was expected. Initial was FL300. But (no Derate) the Aircraft made a level off at around FL245. After almost 6 hrs the aircraft is unable to keep the speed and the level. Thrust is at Max Climb (even MCT or TOGA didnt help a lot). So flying around at FL305 6 hrs after Takeoff and speed is around .765 and it cant get faster or higher. After trying to reach normal speed with toga, aispeed decreases.

MSFS 24SU4
V.1.0.5

VTSP-LSZH
Block 101500kg

ZFW 157900

TOW 259,4

at GW 200t max FL300-303
Speed is hanging around at .76

I know climbing with max weight takes time.... but it should happen somewhen.
 

same issue here

Hi, looking at your ISA (bottom left of the lower SD) I see it's +47 - this is a bug with the sim weather making it MUCH hotter than it should be. Higher temperature = lower engine thrust = can't reach cruise altitude.

Try cycling your live weather to see if it goes back to normal. An ISA of +10 would be considered very hot, +47 is like off the scale hot.

2 hours ago, iniSteven said:

Hi, looking at your ISA (bottom left of the lower SD) I see it's +47 - this is a bug with the sim weather making it MUCH hotter than it should be. Higher temperature = lower engine thrust = can't reach cruise altitude.

Try cycling your live weather to see if it goes back to normal. An ISA of +10 would be considered very hot, +47 is like off the scale hot.

Wow thanks Steven is live real time FS2024 weather issue, my shows +52 ISA at FL370. Using no live default weather or Active Sky live weather fixed this problem at ISA -7/ No performance problem anymore. Glad you guys know what you doing with the planes.

20 hours ago, iniSteven said:

Try cycling your live weather to see if it goes back to normal.

Sadly Cycling live weather normally does not help when I get this bug (luckily I get it only rarely), the only fixes in my experience are restarting the flight, or just not using live weather for the whole flight.

Saw the ISA, could have seen it myself.. damn 😅
yeah, some problems with live weather... 
In my case i discovered it was REX Atmos doing something wrong so live wx wasnt working right
Thx

4 hours ago, Silo01 said:

Sadly Cycling live weather normally does not help when I get this bug (luckily I get it only rarely), the only fixes in my experience are restarting the flight, or just not using live weather for the whole flight.

I suspect this bug is more likely an error coming from the weather model that MSFS is pulling from, rather than an issue with MSFS itself. Hard to say with certainty though.l

On 12/18/2025 at 6:39 PM, iniSteven said:

I suspect this bug is more likely an error coming from the weather model that MSFS is pulling from, rather than an issue with MSFS itself.

Most likely. It already happened back in FSX when I was using Active Sky. Sometimes the data delivered to the weather engine is simply faulty.

Edited December 20, 2025Dec 20 by Farlis

Better late than never, but over on the MSFS forums it was mentioned that if you're running REX Atmos, starting it before the aircraft has loaded in the sim will result in the above behaviour.

I just had the same bug (ironically on the same route, EDW51 Phuket to Zurich), but restarting and following the above advise sorted it for me.