Air France 447 - On topic only!

[TeeVee]

except that BB has made his point several times aside from the stating the very obvious and very pertinent fact that some here have no experience.

and just in case ya missed it, and btw i'm not defending BB, just pointing out the obvious, Evan finally makes a quasi-admission that there is more to flying than books.

"and there seem to be outlying parameters in the Airbus FBW that are not listed in the FCOM or FCTM. "

an understatement to say the least.

now, just so we're clear, as i've said before, i admire his ability to read hyper-technical material and at least appear to understand it. what he has heretofore failed to acknowledge, is that book knowledge alone does not account for much. does anyone here really think that the real investigators are all bookworms and techies? that there aren't at least a handful of real world pilots involved in this and EVERY other air crash investigation?

[Myndee]

Boys will be boys. I'm gonna have to ask ya'll to settle down.

Thanks for the replies. Lots of info for me to consider.

Thank you also for not scaring the shit out of me seeing as I have to fly back home on one of these things on Friday.

Yeah, I have been around for a while, and I consider myself somewhat informed, though not on the level of most of you. I don't think that most airlines want to endanger their pax by using reckless aircraft. It is obvious to me that the limitations that the Airbus computers impose is for good 98% of the time.

This brings me to an example that I would like some feedback on. Remember the heinous attack on the Fedex crew by one of their own several years back (705 in 1994?) Probably the number one factor in getting that plane on the ground was the F/O throwing the dude off balance by diving, rolling, and pulling up wildly. Granted this is a DC10 I am comparing, but if I understand it correctly, the Airbus computers would interpret those commands as being dangerous and would deny them. Am I right? This situation will probably never arise again, and it is an extreme example but I think it is a valid point.

Thoughts?

[Black Ram]

US1549, FBW and Sully's response

Sorry for yet another semi-OT, but this question was raised. This is what the NTSB report says (though I haven't gotten a chance to read the whole thing):

The Airbus simulation indicated that the airplane
performed as designed and was in the alpha-protection mode from 150 feet to touchdown. As discussed previously, the captain’s attention was narrowed, which would have made it difficult for him to maintain awareness of the airplane’s low-speed condition during the descent.

The airplane’s airspeed in the last 150 feet of the descent was low enough to activate the alpha-protection mode of the airplane’s fly-by-wire envelope protection features. The captain progressively pulled aft on the sidestick as the airplane descended below 100 feet, and he pulled the sidestick to its aft stop in the last 50 feet, indicating that he was attempting to raise the airplane nose to flare and soften the touchdown on the water. The A320 alpha-protection mode incorporates features that can attenuate pilot sidestick pitch inputs. Because of these features, the airplane could not reach the maximum AOA attainable in pitch normal law for the airplane weight and configuration; however, the airplane did provide maximum performance for the weight and configuration at that time.

The Airbus simulation indicated that the captain’s aft sidestick inputs in the last 50 feet of the flight were attenuated, limiting the ANU response of the airplane even though about 3.5° of margin existed between the airplane’s AOA at touchdown (between 13° and 14°) and the maximum AOA for this airplane weight and configuration (17.5°). Airbus’ training curricula does not contain information on the effects of alpha-protection mode features that might affect the airplane’s response to pilot sidestick pitch inputs. The flight envelope protections allowed the captain to pull full aft on the sidestick without the risk of stalling the airplane.

This is a brief analysis of the aircraft performance:

http://www.exosphere3d.com/pubwww/pdf/flight_1549/ntsb_docket/431658.pdf

The speed at touchdown was 125 knots.

As for Sully's response to the FBW book, my and others' observation is that he feels the book is taking credit away from him. He did say he could have landed any plane, regardless of type, specifically a "conventional 737". I have heard many note Sully's humbleness, but this sounds a little too cocky to me, as no one can guarantee that, or that the same landing can be recreated with the A320.

I have utmost respect for Sully, but I'm afraid he unintentionally might be in a minor conflict of interest, when getting into such speculation. His exceptional conduct that day should not add weight to his arguments regarding FBW, as this analysis is really not within his jurisdiction.

Now this is really interesting to me:

The National Transportation Safety Board has not issued a final report on the event, but when it does, it is likely to show that there were “flaws in this design,” said Dan Sicchio, a US Airways pilot who represented the pilots’ union in the investigation. “There are things that I hope will come out that will show problems with the control system in this airplane. There were things that helped Sully and things that hurt him.”

So once again, wishful thinking lies somewhere between Airbus being flawed and Airbus being dangerous. Starts to look really pathetic.

[Black Ram]

This brings me to an example that I would like some feedback on. Remember the heinous attack on the Fedex crew by one of their own several years back (705 in 1994?) Probably the number one factor in getting that plane on the ground was the F/O throwing the dude off balance by diving, rolling, and pulling up wildly. Granted this is a DC10 I am comparing, but if I understand it correctly, the Airbus computers would interpret those commands as being dangerous and would deny them. Am I right? This situation will probably never arise again, and it is an extreme example but I think it is a valid point.

Good question. Maybe it wouldn't be the same with an Airbus. However, the Airbus system, at least to my understanding, will interpret the pilot commands as an urgent need to climb/descend and will still provide the max for each, without permitting a loss of control (stall/overspeed). That's for staying in normal law. I'm interested what the more knowledgeable would say.

[Evan]

This brings me to an example that I would like some feedback on. Remember the heinous attack on the Fedex crew by one of their own several years back (705 in 1994?) Probably the number one factor in getting that plane on the ground was the F/O throwing the dude off balance by diving, rolling, and pulling up wildly. Granted this is a DC10 I am comparing, but if I understand it correctly, the Airbus computers would interpret those commands as being dangerous and would deny them. Am I right? This situation will probably never arise again, and it is an extreme example but I think it is a valid point.

Thoughts?

Boys will be boys. Still, the pilot can pull up to 67° of bank in either direction at a roll rate of 15°/sec, and pitch up 30° or down 15° before protections limit him. I think that should be enough to throw an already unbalanced attacker off his feet without losing the wings in the process. But there is no hatchet-attack protection installed on any aircraft that I know of, aside from door locks.

[Evan]

Sorry for yet another semi-OT, but this question was raised. This is what the NTSB report says (though I haven't gotten a chance to read the whole thing):

As for Sully's response to the FBW book, my and others' observation is that he feels the book is taking credit away from him. He did say he could have landed any plane, regardless of type, specifically a "conventional 737". I have heard many note Sully's humbleness, but this sounds a little too cocky to me, as no one can guarantee that, or that the same landing can be recreated with the A320.

I have utmost respect for Sully, but I'm afraid he unintentionally might be in a minor conflict of interest, when getting into such speculation. His exceptional conduct that day should not add weight to his arguments regarding FBW, as this analysis is really not within his jurisdiction.

Once below 100' RA, the stick is in direct law. Control surface movements are directly proportionate to stick inputs. Below 50' RA the system introduces some nose down input to simulate the characteristics of a conventional aircraft, to require the pilot to apply back pressure in the flare. But Alpha Max is the highest AoA it will allow, which is a few degrees beneath critical angle. In a 737, he would have been able to add those few extra degrees of additional pitch but if he exceeded critical angle going into the flare he probably would have dipped a wing and cartwheeled, and I don't see how a 737 pilot is going to know exactly where critical angle is (stall warning has already gone off and he is still pulling). He would have to have a very good feel for stall buffet.

Once AoA exceeds Alpha Prot on the A320, the control law shifts from direct to an AoA demand law. Therefore the A320 allowed him to pull back to the pitch-up stop and let the aircraft interpret that as a maximum safe AoA demand and determine the amount of pitch needed to ride at alpha max, the safest AoA attainable for the situation, without any lost of stability. The result was a pitch-perfect water landing. How could you do this in a 737? You would need perfect instincts. Also, look at the crash in Toulouse, where the aircraft sunk into the trees but did not stall. It remained stable, therefore saving lives. Facing impact with trees, most pilots would instinctively pull to full stop. An A320 pilot can do this without stalling, but a 737 pilot could have pulled up into a stall and impacted those trees in a bank, with more catastrophic results.

I tend to agree that the A320 did some of the difficult work for Sully in this respect and therefore things may have gone differently in the 737, especially if he was indeed trying to pull up beyond a safe AoA. But this is total speculation, and in all other respects he showed himself to be a hell of a pilot under pressure. I don't think anyone should try to take anything away from him, he was PIC and deserves all the credit, but it is also important to point out the obvious advantages of Alpha Prot Law in this situation.

So once again, wishful thinking lies somewhere between Airbus being flawed and Airbus being dangerous. Starts to look really pathetic.

Do you notice how these allegations fail to identify anything specific? That is a sure sign of someone with a weak argument. If you are going to make a statement like this, you need to give Airbus something to respond to. Certainly there is room for improvement, as there is in the now-obsolete 737NG (something Boeing is having to address at this very moment). But I'm beginning to believe that these pilots speaking out so vaguely against Airbus are simply not adapting well from conventional aircraft skills to the new Airbus piloting requirements, and blaming the aircraft instead of themselves.

When and if they get into more specifics, I'll give them some credibility.

[Gabriel]

Once below 100' RA, the stick is in direct law: Control surface movements are directly proportionate to stick inputs.

Evan, are you 100% sure on that. Not that I know better, but if the plane was already in direct mode below 100ft, then it would be behaving just like any conventional plane and there would be no need for...

Below 50' RA the system introduces some nose down input to simulate the characteristics of a conventional aircraft, to require the pilot to apply back pressure in the flare.

... since the plane would anyway require the pilot to apply back pressure in the flare just, like in any conventional aircraft because in direct law it IS a conventional aircraft.

[Evan]

Evan, are you 100% sure on that. Not that I know better, but if the plane was already in direct mode below 100ft, then it would be behaving just like any conventional plane and there would be no need for...

... since the plane would anyway require the pilot to apply back pressure in the flare just, like in any conventional aircraft because in direct law it IS a conventional aircraft.

When passing through 100' RA, pitch goes into FLARE mode, which is a direct stick to elevator relationship with some damping provided by load factor and pitch rate feedbacks. When passing 50' RA, a slight nose down elevator order is applied, requiring the pilot to apply backpressure to maintain the flight path, thus reproducing conventional aircraft characteristics. That's in the A330 FCOM. I'm assuming these aspects are the same in the A320, since cockpit commonality is the Airbus philosophy. I don't have that file with me right now. Maybe you do?

EDIT: Just found that file. The only difference is the numbers on the A320. FLARE mode begins at 50' RA and the pitch down order (2° nose down over 8 seconds) comes in at 30' RA.

[Gabriel]

When passing through 100' RA, pitch goes into FLARE mode, which is a direct stick to elevator relationship with some damping provided by load factor and pitch rate feedbacks. When passing 50' RA, a slight nose down elevator order is applied, requiring the pilot to apply backpressure to maintain the flight path, thus reproducing conventional aircraft characteristics. That's in the A330 FCOM. I'm assuming these aspects are the same in the A320, since cockpit commonality is the Airbus philosophy. I don't have that file with me right now. Maybe you do?

EDIT: Just found that file. The only difference is the numbers on the A320. FLARE mode begins at 50' RA and the pitch down order (2° nose down over 8 seconds) comes in at 30' RA.

I have no file. I told I didn't know really.
But it sounds so absurd!

If you have a direct stick to elevator relationship, then the plane is already behaving like your average 747, DC-8 or Cessna C-150: You NEED to pull up to flare if you don't want to slam the plane on runway.

Why add a "nose down order" to make the plane behave as it is already behaving without that order?????

Now, if you were still flying in some pitch rate demand, load factor demand, or some fuzzy C* or C*U mode, then yes I'd see the need for that since the plane would compensate for the changes in trim due to speed reduction and ground effect (which are what tend to force the nose down).

[Evan]

I have no file. I told I didn't know really.
But it sounds so absurd!

If you have a direct stick to elevator relationship, then the plane is already behaving like your average 747, DC-8 or Cessna C-150: You NEED to pull up to flare if you don't want to slam the plane on runway.

Why add a "nose down order" to make the plane behave as it is already behaving without that order?????

Now, if you were still flying in some pitch rate demand, load factor demand, or some fuzzy C* or C*U mode, then yes I'd see the need for that since the plane would compensate for the changes in trim due to speed reduction and ground effect (which are what tend to force the nose down).

From the A320 FCTM:

When reaching 50 ft, auto-trim ceases and the pitch law is modified to flare law. Indeed, the normal pitch law, which provides trajectory stability, is not the best adapted to the flare manoeuvre. The system memorizes the attitude at 50 ft, and that attitude becomes the initial reference for pitch attitude control. As the aircraft descends through 30 ft, the system begins to reduce the pitch attitude at a predetermined rate of 2° down in 8 second. Consequently, as the speed reduces, the pilot will have to move the stick rearwards to maintain a constant path. The flare technique is thus very conventional.

[Black Ram]

But I'm beginning to believe that these pilots speaking out so vaguely against Airbus are simply not adapting well from conventional aircraft skills to the new Airbus piloting requirements, and blaming the aircraft instead of themselves.

It does really seem they have a personal interest in behaving that way. I have very high respect for Sully, FO Skiles, the cabin crew, the airline for its safety culture and happening to be flying an aircraft with inflatable rafts, etc. After all, an A320 is not smart enough to decide where it is best to land. The pilots decided what to do and the A320 executed their decisions perfectly, better than any human could. US1549 is a perfect example of outstanding airmanship and advanced technology coming together in harmony. Found this interesting analysis form The Times Online:

At the moment of a bird strike, when the engines lose thrust, a conventional aeroplane would try immediately to put its nose down and go into a sharp descent. The pilot would have to haul back on the controls with some strength and to retrim the plane for a slower, more moderate glide while trying to keep the wings level.

None of this is inherently difficult, but it imposes insidious demands on the crew in an emergency, when they are already busy with more important concerns. Imagine trying to disarm a bomb while also having to deal with menial chores and talk on the phone at the same time. Sullenberger and Skiles disarmed a bomb on a three-minute fuse. They did it by concentrating on the two really important matters: how to get the engines restarted, and where to land. They could have done it in a Boeing, too. But it was helpful to their immediate cause that they were working with the product of Ziegler’s mind, in which computers took care of the menial chores, then conjured up a magic carpet for them to fly.

When Sullenberger later gave evidence at the public inquiry into the crash, a French investigator tried to get a bit technical about the Airbus’s role in the miracle.

In private, some of the test pilots and engineers from the Airbus company had been seething for months over Sullenberger’s silence on the subject. Sullenberger is a dedicated union man, as any self-respecting pilot at US Airways should be. But his refusal to mention the unique qualities of the plane was understood as a partisan stand in the context of a long and painful battle between the airlines and the unions, which from the outset rejected the idea that computers fly better than any human can.

This is a complex and emotional subject, since it goes to the heart of a profession already in decline. Nobody dared to bring it up directly at the hearing, or to call attention to the plane’s contribution to the miracle on the Hudson, lest this be seen as an attack on Sullenberger and an attempt to diminish his accomplishment. Nonetheless, for many in that hearing room, it was a subject very much in mind. The Frenchman on the panel certainly seemed to be thinking about it when he asked: “Could you please explain to us how you did choose the airspeed when you tried to do this emergency landing?”

Sullenberger answered with jargon. There was a moment of silence. The Frenchman probed no further.

Soon it was the turn of Airbus’s representative to question Sullenberger. Its team included engineering test pilots who were intimately familiar with the plane and its systems. Their expressions were guarded. For months they had pored over a wealth of information extracted from Sullenberger’s flight data recorder, and they had run multiple simulations of the glide. They knew that the plane’s flight-control computers had performed remarkably well.

The test pilots believed this was a vindication of its visionary design. But they were not going to bring it up. They were going to get through this hearing and be done. They had no questions.

[BoeingBobby]

At the moment of a bird strike, when the engines lose thrust, a conventional aeroplane would try immediately to put its nose down and go into a sharp descent. The pilot would have to haul back on the controls with some strength and to retrim the plane for a slower, more moderate glide while trying to keep the wings level.

The typical sign of a very well informed and intelligent member of the press. NOT!!

[Black Ram]

Maybe a little over-dramatized, but I would think a re-trim would be necessary. Read the next sentence, which explains it is not hard, but presents extra workload to an aircrew, dealing with an emergency.

Since you are at it:

In order for Bernoulli's principle to work there has to be sufficent air flow over the wing.

Not that airflow over the wing is not an absolute must, but isn't the Bernoulli Principle explanation of lift alone by itself oversimplified and outdated? Do classic 747 pilots believe in equal transit time?

[Evan]

It does really seem they have a personal interest in behaving that way. I have very high respect for Sully, FO Skiles, the cabin crew, the airline for its safety culture and happening to be flying an aircraft with inflatable rafts, etc. After all, an A320 is not smart enough to decide where it is best to land. The pilots decided what to do and the A320 executed their decisions perfectly, better than any human could. US1549 is a perfect example of outstanding airmanship and advanced technology coming together in harmony. Found this interesting analysis form The Times Online:

I've never read the report on this so I am unclear on what state the plane was in. If the engines were flamed out, they would have been in Alternate Law, but if the engines were only in compressor stall the gennies and hydro pumps might still be adequately functioning. I'm not sure what law would be in force at in that case. It\s interesting to note that in Normal Law, the flight mode changes to FLARE at 50' RA, but I'm not sure if this happens in Alternate Law. I kind of doubt it, since flight mode transitions to FLARE mode in Alternate Law when the gear is extended. Now that's the interesting part: there is an assumption that gear will always be extended before landing, but not in a ditching... so perhaps the flight mode stayed in FLIGHT mode all the way down...? Or does the ditching switch change that...?

I have to find the report and read it. If anyone has a link, please post that. The statements in the TImes Online article might not take into account the control law reversions that may have occurred.

[Black Ram]

Yes, you can't expect a publication like the Times Online to take note of all the tech details and get everything right, but they are likely to get the politics part.

As for 1549, one of the engines kept running, but was not producing thrust. Also, Sully started the APU right when he took control from Skiles. As far as I understand, they were in alpha protection mode, or what you call aoa demand.

http://www.ntsb.gov/doclib/reports/2010/AAR1003.pdf