I was doing a flight from APYP- RJTT in an A350-900, I took off smoothly with 1+F flaps then raised them later, but when I got to like 280000ft, it stalled randomly. I was only climbing at around 1500fpm and I even lowered it to 700fpm but still no. It has happened multiple times with different aircraft and routes. Can someone please explain why?
I find this situation common with the A330 and A330neo. I think you are flying with too much weight and/or not enough speed for the climb.
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After 28k feet the calculation of air speed will change to mach speed, maybe you stalled because it lowered your speed too much, after 28k it’s better to maintain around mach 0.78 to 0.88-0.89 depending on what your plane is capable of, bellow 28k and above 10k around 300, or at least that’s how I do it.
I used to be confused by this until I saw that the autopilot changed to air speed to mach speed
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Make sure you’re climbing 320 knots airspeed and then 0.85. If you’re doing something slow like 0.65 you’ll have too much drag from the AoA.
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Hi, you stated:
Testing I couldn’t find a combination of factors that caused that to happen, but presumably it is load/density altitude/forward speed related.
Can you give a screen shot of when such a stall just starts to occur, to help narrow down specific causal factors?
The main problem I had was finding the conditions under heavy load where my forward speed couldn’t be maintained at that altitude with the A350.
But as @AndrewWu stated, if you get slow enough, say from not lowering your climb rate until too late, you can get trapped in a low airspeed deterioration the engines can’t pull you out of (without descending). And that is reproducible when testing the A350.
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I never had issues with A359, only with A330 series because I didn’t know the proper vertical speed. I suggest you check this website. As other people said, your airspeed may be too low to begin with. I have some questions tho. When did you retract your flaps? At what altitude? What was your airspeed at the time you stalled?
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Thank you guys for your suggestions. I usually retract the flaps around 1500ft- 2000 and engage A/P (speed) to 250kts. It usually maintains the speed well until I pass 10,000ft and raise the speed to 320-ish kts. It slowly decreases in speed until around 145kts and stalls. It happens with both the A333 and A359. I thought it was wind but i’ve tried everything. I think it’s too much weight and not enough time for the aircraft to speed up. I will try your suggestions and let you know if they work. Thank you agin for your suggestions.
Hi, your added info is very helpfull:
The fall off in speed in the climb to cruise is consistent with maintaining excessive vertical speed.
What can cause confusion: A healthy vertical speed closer to 10,000ft is often unsustainable higher up.
The general rule is: the higher you fly (and the higher the load), the lower your sustainable VS.
Simple way to tell if your VS is too high for your load and the current conditions?:
Your IAS (indicated airspeed) continuing to drop is your warning instrument.
Simplest solution: lower your VS as you see a falloff in IAS until IAS stops falling.
At some altitude your VS will have to be zero to keep IAS from falling (the current cruise step altitude).
Perhaps set a minimum IAS safety goal for adjusting VS downwards: as soon as IAS falls toward that lower limit, VS has to be reduced until IAS can stay above your “never cross below” IAS goal.
If your IAS gets very low (beyond a certain point) but, still well before the stall, simply reducing VS (even with full engine power) will no longer work because:
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Thank you, I have tried lowering the AOA during the climb but I think I lower it too late. I will make sure I keep an eye on the IAS/ Airspeed to make sure it doesn’t drop. I’m doing a flight right now in a 777-200ER from London- Newark. I’ve set the A/P speed to 310kts (As instructed by ATC) and it seems to be slowly decreasing to 300kts. I will do a Step climb (V/S to 0) and was just wondering how long I should keep it on 0 for until I can continue the climb?
Lower your climb rate to maintain 92 n1 and you should be okay. Also when you climb past fl280 adjust your mach number to your cruise speed. Also dont climb right to cruise altitude right off the hop. Step climb your way up to cruise altitude.
Ok, yeah I think that was the problem, I tookoff with too much weight and just left it on +1200fpm the whole way to like 38000ft
Others might give you recommendations on ideas for planning the step climb profile ahead of time, which in essence, takes into account how fast you burn fuel weight.
An intuitive way to see the time approaching to resume climb: your autothrottle will gradually continuously ease off on the power necessary to sustain your current altitude as fuel burns with time.
When throttle power has dropped enough to give you a reserve of unused throttle, that throttle “gap” is what gives you the capacity to resume your climb.
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You should keep it at zero until the total weight of the aircraft drops below 80% (You can check this using the bottom status bar). When you start step climbing, make sure you only climb with roughly 800-1000fpm once at or above 30000ft so that you can immediately save the plane if anything abnormal starts happening again. Another way to ensure safety is doing what @adit just said, you definitely do not want to climb when your throttle is at over 95%
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I use the 70% power as a indicator of when ro climb. Though if you use simbrife it will tell you when of you use vnav to keep yrack of it.
As you can see i am 898nm from FL360 climb point.
I’m at 33,000ft and at 290kts (Ever so slightly lowering). I’m at +200fpm and at 52% load. Should I level off and wait for it to drop down to 50% then continue? (I haven’t fully made a flight plan prior to flight with step climbs but I will next time.). I have the A/P on Mach 0.87 but on the display in the cockpit, it shows its perfectly on speed even though when I was at 310kts earlier, it showed It was on-speed then too? (If I increase the Mach in the A/P, it goes up to 310kts. The auto throttle is only at 80% even though I’m only at 290kts?)
You should be able to climb without any issues with 52% load, just make sure you fpm is lower than 1000 and you don’t go to 40000ft straightaway. As for the dropping airspeed, it happens naturally when you get over 28000ft, and it won’t be an issue until your mach speed drops too low
Ok, when should I level off because the airspeed is too low without getting slow enough that it isn’t realistic? (250kts? 200kts? 270kts?)
For all heavy aircraft after I pass 10K feet I speed up to 320IAS until cruise
You should start levelling off when this happens: the throttle is at 100% but your mach speed starts dropping, which is a real sign that something is wrong. On the other hand, the airspeed drop occurs naturally because mach speed differs with the altitude (e.g. at 1000ft, mach 0.8 would be nearly 500kts of airspeed, but as you go higher, the corresponding airspeed for mach 0.8 would slowly drop past 350kts and down to 240kts or so) It is not technically possible for the airspeed to drop so low that it is dangerous as long as you climb according to the weight and cruise at over mach0.80 and fly below 43000ft (which is as high as the 772’s service ceiling)
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On Simbrief, how do I find the Step climb altitudes when looking at the "Briefing Preview " page? Or do I need to export it into IF to then see the WP altitudes?