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[Chris Scott]

Sorry, HN39,

I'm unable to say whether the displayed VLS allows for cg position, or how much difference it makes. The FMGC certainly calculates where the current CG is, expressed in terms of %MAC (mean aerodynamic chord), but relies on correct crew entry of the ZFW CG. I don't know if there is any independent in-flight verification of current CG.

[In the case of current AUW (gross weight/mass), the FAC (not sure if it's called that on the A330) calculates current AUW independently of the FMGC (so if the crew enters the wrong ZFW before departure, the assumed AUW is not grossly affected).]

By the way, for anyone puzzled, 1.3g is equivalent to a balanced turn with 39 degrees bank. Flying at the 1g-buffet speed is for test flights only. As HN39 indicates, the true "coffin corner" is where the 1g-buffet speed equals MMO [see Editorial Correction below]. Fortunately, very few aircraft (and certainly no airliners) have enough high-altitude thrust to get up there. Flying "on the 1.3g buffet" is fine if you are in reasonably smooth air, and not planning on using more than about 15 degrees of bank.


Quote:
According to Tim Vasquez' analysis, the tropopause level was 15295 m. What is the importance?

I think it is important, and that is very different from the figure (10999m) quoted by mm43.

Flight in the vicinity of a clearly-defined tropopause ("trop.") ** is an unsettled affair. (For the uninitiated, met books traditionally described climb above the trop. as being isothermal; in practice there is a distinct rise in temperature initially as you climb through it.) In level flight, every time you encounter the mixing layer, the SAT (and therefore TAT) go all over the place, affecting IAS and IMN (indicated Mach), the engine thrust changes spontaneously, and the W/V changes. If they had been cruising in and out of the trop., they would have been in that regime. Also, they might have been in and out of the tops of Cbs. (Again for the uninitiated, the trop. acts like a saucepan lid, because of the inversion of temperature associated with it.) That itself is uncomfortable, but unlikely to be accompanied by icing/precipitation.

On the other hand, if the trop. was over 4000m above them (typical in those latitudes), the regime would have been very different. Better in terms of stability away from Cbs; but in the midst of the cells if they entered Cbs. That means severe turbulence, probable precipitation with icing, and high risk of lightning strikes.


** "Trop." is flight-crew slang for "tropopause", and is not to be misinterpreted as meaning troposphere, which is the volume of air between the tropopause and the earth.

[Editorial Correction]
Following HN39's post #2842, the sentence highlighted in red is amended as follows:
"The true 'coffin corner' is the altitude at which, flying at 1g, the onset of the low-speed buffet occurs at the same speed as the onset of the high-speed buffet. In this case, the high-speed buffet occurs at a speed below MMO."