Air France 447 - On topic only!

[Jingogunner]

A nearly faultless explanation

Mr Gabriel

With these definitions, Altitude ASL = Altitude AGL + elevation

Thanks for that comprehensive guide for the numerically inept, Mr Gabriel, all is much clearer. International Standard Atmosphere, Pressure Altitude, Density - as temperature increases, density reduces. We can be sure that readers of the Sun, the Mail, the NY Times etc will not have this information.

[EconomyClass]

Funny how even these online discussions now are hitting the community of Airbus pilots and generating feedback from them.

http://www.wired.com/autopia/2011/07...ance-disaster/

[MCM]

Alasta - The stall warning doesn't need to be active when you are taxiing around an airport, and so below 60kts has been taken to be "on the ground".

[alasta]

Alasta - The stall warning doesn't need to be active when you are taxiing around an airport, and so below 60kts has been taken to be "on the ground".

Thanks. That would explain why it's designed that way, although you'd think that it would be safer to disengage the stall warning only when the gear is lowered. That would ensure that the stall warning is still operative throughout an unreliable IAS situation, but I guess these are the sorts of things that need to be explored as part of the investigation.

[Drizzt]

HeLLo
Here is a link to an Airbus's system explanation....

http://www.airbusdriver.net/airbus_fltlaws.htm

I hope this help....
@@++

[Evan]

Alasta - The stall warning doesn't need to be active when you are taxiing around an airport, and so below 60kts has been taken to be "on the ground".

MCM - The BEA note tells us that the AoA data becomes invalid at airspeeds below 60kts. I think this is because the force of airspeed is not deemed sufficient to accurately drive the AoA vanes. I would think ground mode would be triggered by gear compression or RA alt instead of airspeed, whereas all other flight modes are triggered by RA alt alone.

I can't imagine a high AoA warning occurring while taxiing. Maybe some gust deflection off the ground could cause this?

[Evan]

Funny how even these online discussions now are hitting the community of Airbus pilots and generating feedback from them.

http://www.wired.com/autopia/2011/07...ance-disaster/

Wow, these articles continue to trouble me. Even though this was written before the third interim report released the FDR plots, I can't believe this was written by a competent Airbus pilot, let alone a Captain.

He states:

The key ingredient most everyone seems to be overlooking: The flight control laws of an Airbus. An Airbus has flight envelope protections that cannot be overridden by the pilot.

False.
Since the first ACARS reports we've known that they were in alternate law and those protections were either lost or capable of being overridden by the pilot.

The pilot can always override high speed protection in alternate law.

He states:

Think back to the Airbus flight envelope protections I mentioned, and the fact that the pilot can’t override them. The airplane computers “think” the aircraft is overspeeding and therefore continue to increase the airplane’s angle of attack. That only makes it climb steeper, thus perpetuating this cycle of increasing indicated airspeed and increasing angle of attack. This continues until the airplane is at a ridiculously high nose-up attitude and stalls, regardless of pilot inputs.

False!
This is an entirely false understanding of the protections behavior, especially in alternate law. And the computers knew the airspeeds were unreliable. Who is this guy?

He states:

So the airplane stalled. One plausible theory is what I just described. (There are other scenarios in which the flight control laws are degraded and the airplane can stall under certain circumstances, but that’s a whole other set of seriously complex stuff. Who knows though? Maybe that’s actually what happened.) Even if this guess doesn’t explain precisely what took place, it constitutes a design flaw in the Airbus that needs to be fixed in that the flight envelope protections need to be disabled if they’re receiving inaccurate information.

We've known since the first ACARS were released that the flight controls laws were degraded. When the flight envelope protections started receiving inaccurate information, they disabled themselves. By design. This does not constitute a flaw in the Airbus design.

This article constitutes a flaw in basic understanding of the aircraft by someone supposedly in charge of it.

I think this is something we need to address.

[Gabriel]

Gabriel,

What you have explained here is consistent with my understanding, but I'm struggling to get my head around why the A330's stall warning alarm reportedly goes silent at airspeeds below 60kt even if the AoA is still over the stall threshold. You've stated yourself many times that if AoA is used to detect a stall then airspeed is irrelevant, so why would the stall warning system make reference to the IAS at all?

Alternatively, have I misinterpreted the BEA's description of the A330's stall warning behaviour?

The stall warning is triggered by the AoA vanes, not the airspeed.
But the stall warning is inhibited at too low speeds. As MCM said, you don't want it going on and off when you are taxiing around the airport, although I think that that could be accomplished using a logic that combines weight-on-wheels, spinning wheels and radio altitude. In this way, the stall warning won't be inhibited when the sensed airpseed is low beacues of an airspeed measurement failure, like in this case.

However, remember that in this AF accident, the pilots first go skyrocketting like crazy for about half a minute, then stalled, and then the stall warning sounded uniterruptedly for almost a minute, before it was inhibited by the wrong "below 60kts" measurement. By then, the crew should have surelly have prevented the condition to develop, recove from the stall approach as the stall warning first sounded, and then recover from the fully developed stall. I very much doubt that the continuation of the stall warning after all that would have been of much help.

[guamainiac]

The anonymous Airbus pilot on Autopia I feel is right on the money. He simply states that the aircraft was flown into an area of convective lift where the performance degrades and then information presented to the pilots is questionable ... what they were or were not seeing or was what they were seeing and what the aircraft was responding to.

To me, that last piece regarding the confusing information is the most probable scenario as to why two fellows sat next to each other doing and not doing things that make no sense and violate protocols.

They were faced with informational anarchy in a world that is supposed to be organized and the rules simply are the rules their world suddenly went "anomic" (wrong discipline but the term fits), with no logic and order.

Some that comment on that site miss the point that the aircraft can climb by one other force aside from pilot induced or mechanical (engine/power), it can climb quite nicely just on the updraft whatever system they were entering (and trying to avoid).

One commenter said that on a NOVA presentation on this it was being partly blamed on the lack of the radar to look down. In the Boeing AERO presentation on ice avoidance at altitude they indicate that you should be using the look down (they call it the tilt function), feature to avoid these areas.

What are some of the differences between (if there are any at all), the contemporary radars in use or those on the Airbus or Boeing fleet?

[Fear_of_Flying]

Wow, these articles continue to trouble me. Even though this was written before the third interim report released the FDR plots, I can't believe this was written by a competent Airbus pilot, let alone a Captain.

He states:



False.
Since the first ACARS reports we've known that they were in alternate law and those protections were either lost or capable of being overridden by the pilot.

The pilot can always override high speed protection in alternate law.

He states:



False!
This is an entirely false understanding of the protections behavior, especially in alternate law. And the computers knew the airspeeds were unreliable. Who is this guy?

He states:



We've known since the first ACARS were released that the flight controls laws were degraded. When the flight envelope protections started receiving inaccurate information, they disabled themselves. By design. This does not constitute a flaw in the Airbus design.

This article constitutes a flaw in basic understanding of the aircraft by someone supposedly in charge of it.

I think this is something we need to address.

Indeed, it was pointless to post this article that preceded the third interim report. The pilot quoted also said:

My best guess for AF447 is that the airplane was climbing, most likely due to turbulence

which we now know is patently false; it was due to pilot inputs. In fact, we pretty much knew that prior to the latest report.

Also:

They’re supposed to be difficult to stall, and pilots are trained to avoid stalls. In fact, we train to recover from “approaches to stalls,” not “full stalls” or “deep stalls.” So even if the pilots did everything they were supposed to do to recover from a stall, the airplane still may not have been recoverable once it entered a deep stall and exceeded the critical angle of attack.

Well, we now also know that they did nothing to prevent the stall or recover from approach to stall or even "everything they were supposed to do" to recover from stall - on the contrary, they took the very actions needed to bring the aircraft to a full stall. Moreover, it's hard to believe we still have to guess whether or not the plane could have been recovered once fully stalled. Someone must know.

I'm sure it's frustrating for Airbus pilots and others to hear the great unwashed take these individuals to task, and to "jump to conclusions" as the quoted pilot said (even though the conclusions have turned out to be absolutely correct). However, I guess that's tough luck. Passengers have to be their own advocates, and so far I haven't heard anything approaching an explanation for what the pilots did other than to say they were confused and overwhelmed. That much, at least, we can all agree on.

[guamainiac]

How do we know that it is patently false?

Almost every time you feel a bump in the seat of your pants it is the aircraft trying to climb due to some lift or turbulence.

[Black Ram]

Funny how even these online discussions now are hitting the community of Airbus pilots and generating feedback from them.

http://www.wired.com/autopia/2011/07...ance-disaster/

Wow! That's an Airbus pilot? I think it's just some average moron, or at least I hope so - I really do hope that's not how the real bus drivers are. Protections in alternate law and the computers "fucking up"?

[Gabriel]

How do we know that it is patently false?

Because the black boxes were recovered, remember?

[Gabriel]

To me, that last piece regarding the confusing information is the most probable scenario as to why two fellows sat next to each other doing and not doing things that make no sense and violate protocols.

They were faced with informational anarchy in a world that is supposed to be organized and the rules simply are the rules their world suddenly went "anomic" (wrong discipline but the term fits), with no logic and order.

Really?

[Within seconds of AUTOPILOT DICONNECT]
"I have the controls"
"Alternate law"
"We've lost the speeds"

That recognition of the problem should have triggered a very short and straightforward sequence of actions. Not only that that didn't happen, but they seemed to be doing exactly the opposite thing.

[guamainiac]

Correction, they were doing things but were hesitant and perplexed (or so it seemed), they did nothing that seemed to work.

Sorry. They pushed a bit and pulled a bit and turned a bit.

There is one part of the narrative that says they reduced speed immediately after disconnect, how did they do that?