Air France 447 - On topic only!

[guamainiac]

Did the plane give the humans enough and correct information to do the right thing? They had time to try and sort things out and never came to the proper conclusion and that is a problem.

This is not an open book exam with no limit on time. There is such a thing in the world of exams as a "flawed question" and if the information presented is flawed?

[Evan]

You mean honestly?

Yes, I honestly don't know what you mean by 'AoA Demand Law'. The only place I have any awareness of AoA Demand Law is the Airbus Alpha Protect Law, but that is not for normal flight.

This is what I have in my files describing the B777 C* control law:

11.8.1 Pitch Control
Pitch control is accomplished through what is known as a maneuver demand control law, which also referred to as a C*U control law. C* (pronounced ‘‘C-Star”) is a term that is used to describe the blending of the airplane pitch rate and the load factor (the amount of acceleration felt by an occupant of the airplane during a maneuver). At low airspeeds, the pitch rate is the controlling factor. That is, a specific push or pull of the column by the pilot will result in some given pitch rate of the airplane. The harder the pilot pushes or pulls on the column, the faster the airplane will pitch nose up or nose down. At high airspeeds, the load factor dominates. This means that, at high airspeeds, a specific push or pull of the column by the pilot will result in some given load factor.

That sounds very, very Airbussy to me.

[Gabriel]

Yes, I honestly don't know what you mean by 'AoA Demand Law'.

I meant that, honestly, no, I'm not 100% sure of that. Or 90% sure for the matter.

[Gabriel]

That sounds very, very Airbussy to me.

Yes, only until you add the paragraph immediately following the one you've quoted:

The ‘‘U” term in C*U refers to the feature in the control law which will, for any change in the airspeed away from a referenced trim speed, cause a pitch change to return to that referenced airspeed. For an

increase in airspeed, the control law will command the airplane nose up, which tends to slow the airplane down. For a decrease in airspeed, the control law causes a corresponding speed increase by commanding

the airplane nose down. This introduces an element of speed stability into the airplane pitch control. However, airplane configuration changes, such as a change in the trailing edge flap setting or lowering the landing gear, will NOT result in airplane pitch changes, which would require the pilot to re-trim the airplane to the new configuration. Thus, the major advantage of this type of control law is that the nuisance-handling characteristics found in a conventional, mechanically controlled flight control system
which increase the pilot workload are minimized or eliminated, while the desirable characteristics are maintained.

That sounds very, very NON Airbus to me (and pretty AoA demand)

[Black Ram]

That too. But insofar as the role of automation is concerned, I don't think the attitude will be there was too much of it, the attitude will be it didn't go far enough. That was Black Ram's point, I think.

Yes, my point is the latter is more likely.

[Black Ram]

Wonderful how we can sit at our computers and judge human beings going through hell. Must take a generous spirit to do that. I've seen managers put unwise levels of pressure on workers, then comes and error, and the people creating the pressure then come in and add insult to injury by berating the people who made the errors. Part of qualification to be in the position of power, I guess. It is especially sweet to sit in judgment on the dead. I don't doubt there were errors. I've seen tons of human error in my work life. But I've also sat in the seat where the errors were made. So I know the context. Fact is that the people who helped create the scenario now have their own personal cabooses to keep out of the fire. If you know corporations at all, you can predict what they will do. But those who parrot those responses with no personal loss facing them really lack any excuse. As the old saying goes, dead men tell no tales. It is up to the living to be their voice as this thing goes down. Ultimately, the best defense is the truth, not slanted narratives like "the plane can handle this if the humans do the right thing". I don't know if I can trust BEA totally, but maybe for once the lawyers (the most despised profession on earth) will do their utmost to fill in the part of the story that Airbus, Air France, and BEA leave out. I hope so.

We are still looking into the causes and trying to understand the accident with the limited information released. We are trying to figure out how both the aircraft and the pilots performed. For now it seems the aircraft worked as expected and the crew acted in a bizarre way.
Now imagine for a second some issue did interfere with the pilots' attempts to recover, like the THS preventing a recovery from the stall at FL380 because it locked up - something that for now we know didn't happen. This will add the factor of unexpected aircraft behavior to the list if causes, but the pilots would still be responsible for climbing to FL380 with UAS and alternate law and setting the stage of the stall and the locked THS. And the locked THS didn't even happen.
For what I know, when it comes to air data indications, they did have engine power measurements, altitude, VS, attitude. They also knew FL370 was too high for the conditions, but climbed to FL380 with UAS. Unless that climb to FL380 was uncommanded and they were fighting the airplane while it was doing it, to me this alone sounds like an airmanship fail. In this case they still had a big window for recovery, but not every plane gives you that luxury (Pulkovo 612).
Now, saying the pilots sucked and calling it a day will leave the door open for this happening again. That is why there is a full analysis going on, in the hopes of understanding the crew's perspective. I have a feeling a finger will be pointed at AF and their training program and procedures.
I don't see a specific reason why the BEA can't be trusted. They have pointed the finger at the French pilots of the French airline.

[guamainiac]

Yeah, the crew acted in a bizarre way flying a plane into a 7000 ft per lift with iced pitots into an altitude that is marginal for flight.

And then they may or may not have had information that helped them handle things.

If it doesn't fit, get a bigger hammer?

[Evan]

Yes, only until you add the paragraph immediately following the one you've quoted:

That sounds very, very NON Airbus to me (and pretty AoA demand)[/LEFT]

So, as I understand it, the principal difference between these two control law philosophies is that the Airbus THS will trim for 1G flight irrespective of variations in airspeed whereas the Boeing THS will require trimming to the new airspeed, thus emulating conventional aircraft out-of-trim characteristics in pitch. I don't see how this can be interpreted as an AoA demand law though. They are both load factor demand law at cruise, but the auto stab trim behavior is different.

The other difference is in protections. The Boeing stall protections are deterrents, requiring only breakout force to continue to raise pitch, and the Airbus stall protections are limitations which engage an AoA demand law, removing the need for control column feedback for out-of-trim conditions. Both seem very safe in normal law, but I agree that the Boeing philosophy is better suited to UAS, where stall protections are lost. The 777 will still require manual pitch trim to fly beneath trim speed without backpressure, but I believe the added stall protection deterrent is also lost on the 777 at that point (since it is based on airspeed).

Bottom line as I see it: both aircraft would be defenseless against the pilot actions described in the BEA press release. Yes, the Boeing pilot would have the added indication of 'feel' needed to hold the pitch, but I don't think this was a case of lack of feedback misleading the pilot. I think the pilot would have still pulled up against the yoke, believing (for some reason) that a sustained pitch up maneuver was in order, and he might have even trimmed for the elevator inputs, just as the Airbus did. It also occurs to me that the 777 has relaxed static stability, so the out-of-trim resistance on the yoke, without the artificial addition of the FBW protections, would be significantly less than on a conventional aircraft. How much, I don't know.

And of course, if the pilots had just applied the memory items, this would be a non-issue.

[Gabriel]

Bottom line as I see it: both aircraft would be defenseless against the pilot actions described in the BEA press release.

With that I agree 100%. Let me quote myself a couple of days ago, when we were discussing pilot error vs nasty automation:

Nothing of that, and nothing related to the automation that I can think of, explains why, having positively identified the auto pilot and autothrottle disconnect ("I have the controls") and the UAS ("We've lost the speeds"), they didn't follow the memory items or, at the very least, stabilized the plane in a normal cruise pitch and thrust setting as they were flying just up to then, but instead pulled up 10 deg nose up without increasing the thrust, climbing from FL350 to FL375 at vertical speeds that reached 7000 fpm, and then, when the stall warning sounded, they PULLED UP AGAIN until reaching 38000ft with an attitude of 16 deg nose-up. I can't imagine why they would have done anything of that different in a Boeing.

For the rest of your post, I invite you to follow it via PM, since the 777 FBW is off topic, and especially not useful for the forum when discussed by people who just don't know much about it like you and me.

[Evan]

For the rest of your post, I invite you to follow it via PM, since the 777 FBW is off topic, and especially not useful for the forum when discussed by people who just don't know much about it like you and me.

I don't think it's off-topic Gabriel. There has been a lot of insinuation about the airframe being the cause and not the pilot, or the Airbus cockpit/pilot interaction, the pilot being left 'out of the loop'. I don't see that playing a role when the pilot clearly violates the basics of UAS and approach to stall. I think he would have done the same on the 777, just more forcefully (yes, I realize that you agree with this). That's the point I'm trying to make. Maybe more information will arise to change that perception, but I would expect anything of that nature to have been released as a bulletin to operators by now. Meanwhile, speculation and rumors continue to fly about how the plane prevented the crew from taking control and they had no instrumentation because the automation flipped out on them, and this wouldn't have happened in a non-Airbus jet. There is nothing to support this in the BEA reports.

I agree that we shouldn't be getting into a protracted technical analysis of the 777 flight control systems here. But I think the point is made. PM me if you have something to add or correct though.

[EconomyClass]

Easy to say that at a keyboard with no responsibilities.

[Myndee]

Good Lord almighty am I confused!! I go away for a while and arguments ensue, and now I don't know who to listen to.

I just flew my third A320 trip. I really can't say anything bad about these planes. Very comfortable flights.

I am not going to ask a crapload of questions. All I am going to ask is:

AIRBUS COMPUTERS...BAD or GOOD??

[Fear_of_Flying]

I go away for a while and arguments ensue, and now I don't know who to listen to.

"...arguments ensue." That's a charitable way of putting it. As for who to listen to, I guess it depends on who you ask.

But come on, you've been on this forum for a long time, you know more about aviation than the average passer-by, do you really think the Airbus is inherently unsafe, or any commercial air travel amongst major carriers for that matter? I would hope it would take more than a few screaming banshees to give you cause for concern.

[Gabriel]

All I am going to ask is:

AIRBUS COMPUTERS...BAD or GOOD??

Yes.

[Black Ram]

AIRBUS COMPUTERS...BAD or GOOD??

Just like with your average HP, it's good for the first 1-2 years, while the warranty lasts. From then on, you better have a back-up of all your data.