I wanted to fly today from EGLL Heathrow to OMAA Abu Dhabi. But when I reached FL270 the plane started slowing down from 485kts ground speed. When I reached and levelled off at FL390 which was my cruise altitude, it kept on getting slower and the nose began to raise up causing the aircraft to stall and drop.
The aircraft was the A380.
I also wanted to fly earlier today in the morning with an a330 from EGLL to KJFK John F Kennedy and the same thing was happening.
I am a frequent infinite flight user and I am now on grade 3 and had more than 290 flights and most of them are long haul ones and never experienced something like this until today.
Maybe if you look at the wind, this occurs alot if I have tailwind. What I normally do is to decent to an lower altitude and put V/S on 0. To obtain more speed. If I have a normal cruise speed I step climb to the alt. which I want to cruise (mostly stepclimb with 100 to 250m/s)
False. FL270 isn’t that high. Even for a fully loaded A388. Which shouldn’t be the case as that flight is less then 10 hours. But if the op climb at an insanely high VS then there’s an issue.
OP here’s something i hope helps.
Here’s a website to use for weights and everything https://fpltoif.com/
And here’s well it’s self explanatory A Guide to Step Climbing
If your V/S was too high that could be why. Once i reach FL200 I put my V/S to 2000, then at FL250 1500. Then at Fl300 and above 1000. (Depending on my aircraft and weight)
That can’t be true. Ground speed won’t make you stall, if your IAS drops then you will stall. But if your IAS was 485 knots you’d be way over speed and your airframe would literally rip itself apart, so the reason must have been IAS, except you were looking at your ground speed. As mentioned above, stepclimbing will probably solve the issue
This is normal actually.
Below FL280, the autopilot uses IAS, and your TAS will increase.
At above FL280, the autopilot transitions into mach speed. Your TAS will decrease until you hit a point where the temperature of the atmosphere stays constant, usually somewhere between FL320-400. Then your TAS won’t change anymore.
Your ground speed could also be changing because changing winds.
You are right. Between 25000-30000 ft this is the altitude of conjunction. Your speed above switches into Mach speed. Mach speed is a true air speed in Mach.
Apart from winds changes nothing else should change your ground speed.
I also remarked this problem when I used to fly with Infinite Flight. It’s as if they calculate GS from IAS instead of TAS. An A380 pilot friend confirmed it to me. He also told me “if ground speed decreases as much as it is I will not fly FL410”.
My airspeed decreased from 240kts when I was about 37000ft down to 140. I disengaged the autopilot and descend the plane manually to FL200 then continued with A/P back to Heathrow EGLL.
Maybe it’s because I was climbing at 2600ft/min and the elevator trims at 9%.
Yeah, 2000 fpm is a bit high, but it shouldn’t really affect how you stall too much, that’s probably due to not stepclimbing, in that case, check out the links above 👆. Not having enough trim won’t affect the stall speed, but can I ask what the auto throttle was doing? If you climb at 2600 fpm at that altitude and that weight the engines might not have been strong enough to keep the plane at speed, was the aurtopilot trying to speed up or was it just sort of letting you stall?
My friend A380 pilot answer: “Let’s say I’m FL400 M0.8 my GS is around 480. If I descent my KIAS will increase until reaching 300 kt at the altitude of conjunction (around 28000ft). At this moment speed passes from Mach to KIAS. My GS is still 480”
Otherwise it would be completely stupid to fly over FL280.
Mach speed is a TAS not a IAS. Otherwise it would not be a number of times of sound speed (which is a true speed). In other flight sims GS is stable over FL280 (regarding the winds).
But when I used to fly with Infinite Flight I had supposed it was an error of displaying without really impact to GS (GS descreases but in fact the plane keeps its speed).
The none GS variation can be also seen in FlightRadar24.
You will notice that 480 at M.80 means 600knots M1.0. M1.0 at sea level is around 670 knots. Speed of sound decreases by altitude.
The altitude at which speed of sound stops changing actually does differ between different locations on earth. Where does your friend fly actually?
btw good explaination here https://www.quora.com/Do-airplanes-fly-faster-at-higher-altitudes
M0.8 means M0.8 471 kts GS (yes I admit it’s not 480 kts).
He flies often LFPG-KLAX or KFSO at M0.85 every fly starting from FL370 to FL410 as you have to do with an A380.
I’ve just asked him for a photo of the PFD where we can see all speeds.
