So I was doing a flight in the A320N Fly by Wire. I put the autopilot on and cruised for about 50 minutes at 38,000ft going 0.82 mach. Then I leave for 2 minutes to grab something I come back and and it says the aircraft overstressed. I have never had this happen and I probably have around 50-100 hours flying the a320. Anyone have a guess of what happened?
Whoa. That’s not fun. Just a guess: you ran into a major wind shift or headwind that brought you way over max speed??
0.82 mach is way over the A32N’s normal tolerance. You’re lucky it didn’t happen sooner.
Pretty sure 0.82 is cruise speed A320neo - A320 Family - Airbus
Can’t think of would else would of caused it. Sometimes when the live weather updates wind speeds increase somewhat drastically so I guess it was just a way bigger change than normal.
depending on your weight your were pretty much flying in coffin corner.
Not smart to leave it unattended on AP at those speeds / flight levels.
probably better to drop to mach .75 when you want to go afk.
Which version of the mode are you using?
M0.82 is MMO (maximum operating Mach), so you would have been right at the edge of the overspeed warning band. Still, that wouldn’t cause an overstress by itself. Did you happen to put it on active pause or something?
The stable version uses the original default structural load limits, which are too low. The developer version has updated load limits (all but one of which Asobo also updated in the default airplane) to match the real airplane. It is very difficult to overstress the developer version, especially with the FBW system working. Once the custom FBW system is finished, it will protect the airplane from a structural overstress condition.
Would have been interesting to see exactly what caused your overstress!
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That page lists the A320’s MMO as mach 0.82, and the MMO is essentially your never exceed speed. Someone else in the thread mentioned the coffin corner, and I agree that you probably hit some atmospheric change (e.g. colder air) that resulted in the aircraft exceeding it’s max aerodynamic pressure limits.
Check out the bold method’s article on MMO and the coffin corner.
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So we agree. 0.82 is too fast at that altitude
It’s too fast at any altitude, although it will not lead to instant disintegration.
Mmo is the maximum operational Mach number, but there is still a safety margin there. Now if you reach Mne, that is another story. Because then you have flow separation and will almost certainly die, because you don’t have enough elevator authority to counter the Mach tuck.
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There is no Mne in a transport category airplane and no worry about Mach tuck or “coffin corner” in the A320. M0.82 is an acceptable speed to operate at as long as there isn’t too much turbulence. There is safety margin built into that speed, and there is plenty of margin between normal cruise speed (around M0.78) and stall speed.
Would agree normally, but seeing as this is a sim, and weather occasionally just pops to new parameters, it’s better to be safe than sorry.
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The easy solution is to fly at normal cruise speed of 0.78 ALL THE TIME.
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Why not?
True. I was generalizing.
That’s what I wrote.
Easier solution… keep it at managed airspeed mode.
@Descorcho The thing about the selected mach mode is that according to my observation. They tend to change, the overspeed limit sometimes drops down, sometimes rises up. So when you’re cruising where the 0.82 mach is available you can do so at first. But as soon as something happened, either wind or air pressure changes, the overspeed limit may drop down do 0.8 or 0.79 mach. At this point, you would still be flying at 0.82 and overspeed the aircraft.
So the best way to fly at cruise is just leave it on managed mode.
True, I have to admit I assumed that everyone flies the A20N in managed mode as you’re supposed to. Why would you ever cruise in any other mode?
I do sometimes switch to selected mode if I want to speed up my flight. Especially when flying with a headwind. But doing so would need me to standby really close. As soon as the warning alarm rings, reduce to 0.79… then as soon as the upper limit opens up, slightly increase the airspeed again.
But usually when I’m on a 8-9 hour long haul flight on the A320 and I have to leave my PC. Then it’s safer to just use managed mode.
You can program in a cost index that is very high (like 99) so that the aircraft flies in managed mode at the fastest it can. Selected speed is not standard procedure in the cruise.
Yeapp… I always set my CI to 100.
Or on long haul where I want to save fuel would be CI 0
Well, like I said there is a reason that the Airbus standard procedure does not want you using selected speed mode. But this is a simulator so go ahead and do what you want. But don’t be surprised when the aircraft breaks.
If you’re in such a hurry, just use the “jump to” feature in the Nav Log(I think?). One of the options in the pull down. You can skip straight to the TOD.