[ml/nj]

This could have been wind shear

One wonders why you would post when you obviously know nothing about what you are talking about. Posts like this would make me question EVERYTHING YOU EVER POST.

Wind shear is a problem when you are low and slow. (I.e. takeoff and landing.) It is not a problem when you are high and relatively fast. When you are low and slow you might be only 20 knots above the stalling speed (that speed at which the wings no longer generate sufficient lift to keep the plane aloft). So a sudden loss of 30 knots due to wind shear would cause the plane to begin falling. (NB Falling and descending mean different things. I said falling.) When you fall close to the ground bad things happen.

At 35,000 feet (or whatever) the situation is somewhat different. Usually you have much a much greater speed margin over the stall speed. But even if you do stall, you just fall. In all but the most unusual circumstances, the fall increases the speed of the air over the wings and lift returns. Even if this takes several thousand feet, there is no ground anywhere near enough to cause a problem. I really don't know how much altitude the big boys would be likely to lose during a stall recovery but my recollection is that someone just learning to fly a single engine plane (which I did over 30 years ago) is expected to be able to recover from a stall without losing more than 100 feet of altitude.

ML/NJ

[Vendome]

Thanks for your post. I was going to reply but skipped it. I experience wind shears in the DFW and will route my summer flights with NO Stopovers in DFW.

[justlurking]

One wonders why you would post when you obviously know nothing about what you are talking about. Posts like this would make me question EVERYTHING YOU EVER POST.

I also wonder why you would reply to my post without reading all of it. I point out that wind shear is generally a "low and slow" problem.

But, there are a number of issues:

• ACARS reported the deviation in speed, but unless you happen to know what the threshold is, I haven't seen any indication of how much a deviation is required to trigger the report. It doesn't necessarily mean the airfoil had stalled.
• If the aircraft slowed to manuevering speed in turbulence, it would have put them closer to any reporting threshold.
• Weather reports say there were huge updrafts (in excess of 100 mph) in the area.
• As I'm sure you know, indicated airspeed is significantly less than true airspeed at 35,000 feet.

However, I didn't mean to imply that's what caused them to "fall out of the sky". The deviation in airspeed is really more of a symptom: perhaps that they were encountering severe turbulence. Or maybe that a structural failure put the aircraft into an unusual attitude that reduced the indicated airspeed and triggered the report.

[justlurking]

I was looking for the article that mentioned a maintenance issue with the plane prior to this flight, and found this. Perhaps it will explain my point a bit better:

The Pilots' View on Air France 447

Saunders also notes that if you’re caught in a storm at cruising altitude, where the air’s thin, the “buffer margin” on how much you can speed up and slow down narrows greatly. Current Airbus models are electronic wonders engineered to minimize the danger from human mistakes. They won’t fly faster than design specifications allow and they don’t let themselves stall. But an electronic problem could grow to a point where the computers could be disabled or given incorrect data. Without trying to condense Saunders’ technical explanation of stall speeds and engine thrust into a big inaccurate mess, suffice it to say that flying one’s way out of a severe storm at 35,000 feet is far trickier than one can imagine. A violent interaction of lightning, updrafting winds, and hail could produce a very ugly environment for an airplane.