Green dot

[michelda]

Good morning,

A321 Neo… somebody knows why green dot is behaved like that at FL 390? And why there is a limit at 292kt?

[321XLR]

Originally Posted by michelda

Good morning,

A321 Neo… somebody knows why green dot is behaved like that at FL 390? And why there is a limit at 292kt?

what? behaved like what?

[RudderTrimZero]

Are you referring to the situation where Green Dot ends up below VLS? I thought that bug was fixed over 5 years ago?

[michelda]

At FL390 green dot is not following “standard” law of increasing with altitude.
At GW of 100t, above FL300 green dot unchange

[ScepticalOptomist]

Originally Posted by michelda

At FL390 green dot is not following “standard” law of increasing with altitude.
At GW of 100t, above FL300 green dot unchange

Seems the “law”‘doesn’t get followed from 70T and above FL350 either!
Airbus Aerodynamics can be a fickle subject.. :-)

[Jonty]

Originally Posted by michelda

At FL390 green dot is not following “standard” law of increasing with altitude.
At GW of 100t, above FL300 green dot unchange

Probably because 292kts is well above VMO.

[waterbottle]

How are you getting a 100t A321 to FL390?

I get a Rec Max of FL331 at 93.5t.

[Check Airman]

I vaguely recall this being addressed in one of the issues of the Safety First magazine.

[Jonty]

Originally Posted by waterbottle

How are you getting a 100t A321 to FL390?

I get a Rec Max of FL331 at 93.5t.

I seem to remember that MTOM in a XLR is only 97T

[hikoushi]

Taken on a NEO at FL390…. Fairly positive 292 knots would be destructive at that altitude!

[321XLR]

Originally Posted by hikoushi

Taken on a NEO at FL390…. Fairly positive 292 knots would be destructive at that altitude!

that is a pretty narrow window between VLS and barber pole. What was your "OPT altitude" per the box?

[B2N2]

Originally Posted by 321XLR

that is a pretty narrow window between VLS and barber pole. What was your "OPT altitude" per the box?

From a Boeing guy that looks alright to me.
Then again what do I know.
(Checks door)

[Check Airman]

That looks fairly normal for a heavy A321 up high.

[hikoushi]

Originally Posted by 321XLR

that is a pretty narrow window between VLS and barber pole. What was your "OPT altitude" per the box?

IIRC around 375 - 380. REC MAX was pegged at 398. Was a nearly empty flight (COVID era) but fuel heavy. Climbed up to avoid being stuck way lower. VERY smooth day otherwise would typically never go that high above optimum (ask me why!).

[CaptainOrange]

Originally Posted by B2N2

From a Boeing guy that looks alright to me.
Then again what do I know.
(Checks door)

Haha... That does look a bit tight for us bus guys actually. Not completely uncommon but usually we have some more margins when around optimum levels.

[Gero]

That margin will be ok even in moderate turbulence. Checked more than once.

[Mr Good Cat]

Green dot is always on VLS at MAX ALT in our 321 NEOs, whereas on the CEO there's usually a very small gap.

[michelda]

Thanks all for your replies!!

Just few more question. I think Airbus knows that at FL 390 is not possible to fly at 292 kt…..so why they inserted values instead of dashes or blank box?
I agree that at high altitude the green dot value is equal to vls, but how can be lower than at low altitude?

[hikoushi]

Originally Posted by Gero

That margin will be ok even in moderate turbulence. Checked more than once.

….how many times have you personally actually experienced legitimate moderate turbulence while flying with those performance margins? 🍻

[Mr Good Cat]

Originally Posted by michelda

I think Airbus knows that at FL 390 is not possible to fly at 292 kt…?

You could do a straight 'unloaded' dive at FL390 at 292kt (like they do during manufacturer's test flights), and you'd be doing Mach 1 exactly. This won't break anything unless you put any significant load on (like a rapid yank to get your nose up), but I imagine the buffet is quite strong. Any load on the wings and you wouldn't technically be 'flying' at that speed of course, just high speed stalling

When they did the flight diving test on the 777-300 the T33 chase plane clocked them at 1.01M. Not sure of the altitude at which it happened.