Originally posted by opa-opa
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Originally posted by Gabriel View PostIf an updraft hits, then the wind will come not horizontally anymore but more from below. Voila, the AoA has just increased.
Thanks, I see it. But how monstrous does that updraft have to be in order to catastrophically stall the airplane, given it is also going forward at cruising speed? The updraft airflow is not the only airflow.
The only such case I have heard of is from the 60s, involving a 707. The updraft apparently made the airplane go dangerously nose-up, which is what led to the stall. And the airplane was not lost until it was hit by a similarly severe downdraft during its stall recovery, which led to nose-up commands that overstressed the airframe.
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Originally posted by Black Ram View PostThanks, I see it. But how monstrous does that updraft have to be in order to catastrophically stall the airplane, given it is also going forward at cruising speed? The updraft airflow is not the only airflow.
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AirAsia QZ8501: 'Pings' detected in plane search
"Pings" have been detected in the Java Sea which could have come from the "black box" of AirAsia flight QZ8501, officials have told the BBC.
There has been no confirmation yet that the signal has come from the flight recorders of the missing jet.
The commander of the Indonesian armed forces, Gen Moeldoko, said he was now worried that the flight recorder may not be in the tail, found two days ago.
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Originally posted by Black Ram View PostThanks, I see it. But how monstrous does that updraft have to be in order to catastrophically stall the airplane, given it is also going forward at cruising speed? The updraft airflow is not the only airflow.
Now, at 350 kts TAS (as apparently this plane could have been going according to some radar data) every 30kts of updraft will increase the AoA in 5 degrees. 5 degrees can very well be the difference between not stalled and fully stalled, especially if you are flying at 350 kts TAS at 36000ft which should be a quite slow airspeed and hence a quite high angle of attack to begin with. And of course there is not law of Physics that limits the updrafts to 30 kts max either.
The only such case I have heard of is from the 60s, involving a 707. The updraft apparently made the airplane go dangerously nose-up, which is what led to the stall.
An updraft, if left unattended, will create only a transient increase in the AoA. The plane can transitory stall but it will unstall itself with no pilot intervention (human or otto).
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
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Originally posted by Evan View PostThe danger lies in incorrect pilot intervention.
On the other hand, if a strong and continuing updraft is encountered, there can be considerable danger if a pilot does not intervene.
One scenario I can envision is encountering an updraft while the autopilot is engaged in altitude-hold mode. The AP will lower the nose in an attempt to maintain altitude, which will make the aircraft's speed tend to increase. Most likely the autothrottles would be engaged at the same time and keep the speed increase in check, but if the nose is pointed down enough the plane's speed could increase even with the engines at idle, resulting in an overspeed condition.
Another possible scenario is if either the autopilot or the human pilot tries to maintain pitch attitude instead - basically trying to "ride out" the updraft and allow altitude to increase. It's possible if the plane's altitude increased enough that in the thinner air it could stall which of course would be bad.Be alert! America needs more lerts.
Eric Law
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Originally posted by sjwk View PostOr perhaps not...
Originally posted by NY TimesSupriyadi, operational officer at Indonesia’s National Search and Rescue Agency, said his team detected pings in their efforts to find the black box flight recorders from AirAsia Flight 8501.
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Originally posted by elaw View PostAnother possible scenario is if either the autopilot or the human pilot tries to maintain pitch attitude instead - basically trying to "ride out" the updraft and allow altitude to increase. It's possible if the plane's altitude increased enough that in the thinner air it could stall which of course would be bad.
Stall is not a matter of airspeed, thin air or you name it. It's all about AoA (ok, and little bit Mach too).
The plane will not stall in this case (unless the pitch the pilot is trying to hold is too steep). The plane will just descend. Now, if after exiting the updraft the pilot wants to hold the altitude instead of the pitch, that is the recipe for the stall.
Stall happens when the pilot (human or otto) tries to hold the altitude that the plane doesn't want to hold.
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
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Originally posted by Gabriel View PostStall happens when the pilot (human or otto) tries to hold the altitude that the plane doesn't want to hold.
I think there's a psychology working against descending into storms that might override approach-to-stall procedure in some not-so-well-trained pilots.
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Strange how this section has torn off. The "cheap composite" fin lugs held (like they did with AF447) suggesting the loads were longitudinal, as in an impact. The rudder is also still attached. I'm guessing this did not result from a midair breakup (although one might still have been the cause of the crash). From what I can see the FDR's would not be in this section but it sounds like they have located them nearby. So I'm expected those to show up in the next few days...
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Another thing I noticed is that some of the interior cabinets and the general remains of the fuselage do not appear to show the high-vertical impact stress seen in AF447, which might suggest a mid-air breakup. Parts of the rear bulkhead appears to be torn outward but all of that could have happened whenever the final destruction took place.
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Originally posted by Gabriel View PostNo.
Stall is not a matter of airspeed, thin air or you name it. It's all about AoA.
And stop the bull crap that airspeed and high altitude don't matter.
An unstalled airliner at 20 kts isn't worth a whole lot, and a plane at coffin corner is a wind gust away from falling out of the sky in a stall.
Like I said elsewhere- good airspeed control is essential so that you almost never hear even a warning of a stall. (And don't pull up relentlessly and mindlessly).
Yeah it's an AOA/attitude thing but the management of speed and high altitude is kind of critical too.Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.
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