A359 Randomly Stalling

While in-flight from EIDW-KJFK, I reached my cruising altitude of 40,000ft in the A350. Then, at M.84, my plane started rocking inexplicably from side to side, and losing speed. I was away when this happened and only know it from my replay. I reached it in time to slow down the altitude loss and eventually settle the plane at M.60 and 36,000ft. I set the altitude to 40,000 again and the speed to M.80 to try get back on track. I went away again, for breakfast. When I came back I found my plane had stalled again and crashed. I also got a violation. How does a plane stall at cruising speed and does anyone have an idea why this happened?
Thanks,
@CaptainHugh

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From the sounds of it you were too heavy for your cruise altitude, you should step climb to avoid this happening. Also, no plane randomly stalls.

Here’s a tutorial by Matt on step climbing

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check the weight of the aircraft or speed

I did stepclimb. Thanks anyway

Hmm, how far into the flight did you do the climb up to FL400?

Weight: I don’t know
Speed: M.83 at the time of the first speed loss

Well I stepclimbed all the way to FL320 and then went direct to FL400. I was about 200NM into the flight. I’ll have a read of the thread.

You should have stayed at FL320 for longer as climbing from FL320 to FL400 in one shot, 200NM after departure and all while being heavy, sounds like a disaster waiting to happen.

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You are too heavy for FL400. Also cruise for A350 is .85-.86

BTW I did some fuel testing a while back. At .85, the highest efficient altitude is FL340 for some reason.

Thanks! Appreciate it

At what weight were you at when you figured this out? Do you have any fuel flow numbers by chance? I’m curious cause FL340 is really low for an A350-even with a heavy load IRL they usually go up to at LEAST FL360/380 initially and then wind up at FL400/410.

Something similar to this happens in the A330-300. The power to weight ratio at cruise seems super low-there’s plenty of power at takeoff for even reduced takeoffs, but trying to go the normal A330 cruise speeds of M.80-M.82 at say an initial level of FL360 is taxing on the engines-they run at 100% THR/Max N1%

It seems like the “coffin corner” as it were is narrower in IF than it would be IRL. I’m wondering if this is something Laura can tweak down the line in future updates to make it more realistic.

Even DL295-an A359 from ATL-NRT (~14:00) almost always (with exceptions for weather avoidance it would seem) starts out at an initial cruise level of FL360 and then step climbs about 2-3 hours later to FL380 then stays for an extended period (4-5 hours) at FL380 and winds up at FL400-410 by the tail end of the flight. But again-the initial is FL360 95% of the time it seems (I checked samplings of flights over the last month or so)

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Hello,

I’m like you with the A350 with which I fly regularly. I also used to make it climb to an altitude of 40000fts with a speed of M 0.86
However, to avoid the inconvenience you have experienced, I do not do it from takeoff. I do it step by step and depending on the weather, taking into account especially the force of the winds and the weight of the plane because in general I have 325 passengers and a freighter of 21,059 and I always put the equivalent of two hours more than the expected flight time in terms of fuel. So, if my flight lasts 2 hours I will put 4 hours of fuel.

At takeoff so I always raise it to 35000fts with a speed of M 0.85 then I wait to see its behavior, the zones of turbulence if they are present then approximately 20 to 30 minutes at this rate I raise it to 38000fts if I am in corridors with strong winds or directly at 40000fts if I am on a calm weather. And from that moment on, I can go do something else with the assurance that I won’t find my plane in the middle of a crash.

I am not telling you that it is the most relevant solution because it all depends on your own parameters including the weight of the plane and the weather but I work in this way and so far I have had no problems. Good luck.

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Yes this happend to me in the 777 it’s like a wind shear kind if thing and the autopilot being garbage and at 40,000ft you could be too heavy and delicate movements like this in high altitudes can and will cause speed loss and you probably got the violation while stalling (if you havent figured)

When the A350 came out I did some testing at M85 and different fuel/FL combinations. At anything above 190t, flying above FL350 was inefficient.
I did a 10000nm+ flight at FL310 and 330 so defnitely not gonna run out of fuel.

Does trim affect A350 fuel by any chance (in IF)? I know it does not on other planes (at least not that I know of).

Too slow for cruising speed on an A350, A350 cruising speed is Mach0.85

Theoretically it SHOULD-if you don’t zero out the trim (magenta bar) at cruise, you’re interrupting/not optimizing airflow. In addition, iirc the A350 has drooped ailerons and flaps during cruise to optimize the wing-the lack of simulating that could be part of the reason she can’t get up and go like she should. The A330 on the other hand seems to be a power to weight thing.

I just did a test and it does not in IF. Apparently IF just implements trim as a constant elevator input. The only reason to use trim is to prevent AP on certain planes (like a380) from crashing the plane.

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