smittyone
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What Is It Like 'hand Flying' An Airbus?

Thu Aug 02, 2012 1:09 pm

Not trying to start a flame war or get into a gun battle over the different control philosophies here.

I'm just curious to hear from Airbus pilots - what is it like to fly with the side stick? Is it easier or harder than a conventional yoke? Does the computer system take up some of the workload of keeping the wings level or maintaining a desired pitch angle that you would have to do for yourself with a Boeing's yoke and trim controls?

Is there a mode where you are directly controlling the ailerons/elevators with no computer intervention? Seems like that would be much harder to do with a stick. Would you have to manually trim in that case?

I have about 40 hours in Cessna 172s so I have a rudimentary understanding of flight controls. But the Airbus system is a bit of a mystery still.

Thanks -
 
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Starlionblue
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RE: What Is It Like 'hand Flying' An Airbus?

Thu Aug 02, 2012 1:58 pm

Quoting Smittyone (Thread starter):
Is there a mode where you are directly controlling the ailerons/elevators with no computer intervention? Seems like that would be much harder to do with a stick. Would you have to manually trim in that case?

Yes. This would be Direct Law. In Direct Law no pitch autotrim is available. However I don't know if any FBW Airbus has ever gone into Direct Law in line operation. There is also a "Mechanical Backup" law even "lower" than Direct Law, where all you have is stabilizer trim and rudder. I'm pretty sure that has never been degraded to.

See here for an excellent summary of control laws: http://www.airbusdriver.net/airbus_fltlaws.htm
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airmagnac
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RE: What Is It Like 'hand Flying' An Airbus?

Thu Aug 02, 2012 3:04 pm

Quoting Smittyone (Thread starter):
But the Airbus system is a bit of a mystery still.

Consider it as a translation device. It is translating pilot inputs (load factor/pitch rate, roll rate) into control surface deflection angles.
Here, translation means doing lots of relatively complicated calculations over and over again at a high frequency, with lots of variables. The human brain (=pilot's brain) is a wonderful computer, and does this work fairly well on traditional machines. But a dedicated computer does it a lot better, and can do a much more optimized job.
That's the whole point of flight control laws. And those are made much easier to implement with electronics and electric signaling, ie Fly By Wire.
These laws can be implemented on mechanical designs, but it is much more difficult. (after all, there is a simple law that transforms a single lateral demand into two surface deflection angles (ailerons) on your C172).

That's why we abusively talk about FBW or non-FBW, whereas the difference is more on the lines of "lots of sophisticated control laws" vs "a few relatively simple ones"


The idea is the same for any FBW aircraft, be it Airbus or Boeing or Embraer or Dassault or whatever. The main difference between A & B is that Boeing decided to use FBW and computers while keeping a traditional feel for the cockpit, whereas A decided to adapt their cockpit to the new control structure.

Quoting Smittyone (Thread starter):
Does the computer system take up some of the workload of keeping the wings level

If you leave the sidestick in neutral position, then you are asking for no roll rate. So the flight control computers will move the surfaces as required to maintain the current lateral attitude. So if you have wings level and stick neutral, the plane will work to maintain wings level without any pilot input.

Quoting Smittyone (Thread starter):
maintaining a desired pitch angle

Same as above : if you are in the stick's neutral position for pitch, you are telling the plane to hold its current attitude. (it's slightly more complicated because the input is actually a blend of pitch rate and load factor, but the general idea is the same)

Quoting Smittyone (Thread starter):
you would have to do for yourself with a Boeing's yoke and trim controls

Correction : you would have to do for yourself with a traditional mechanical linkage flight control design .
The critical difference is not in the cockpit design (yoke or stick), but in what is between it and the control surfaces.
A Boeing 777 or 787 or any other FBW aircraft will behave in approximately the same way, except that you have to trim for speed variations on the 7x7s.

Quoting Smittyone (Thread starter):
Is there a mode where you are directly controlling the ailerons/elevators with no computer intervention? Seems like that would be much harder to do with a stick. Would you have to manually trim in that case?

Alternate control laws : pitch is still a load factor demand, so the computers still calculate the appropriate deflections of the elevators and pitch trim. Lateral is direct
Direct law : Aptly named as controls are direct. Including pitch trim (ie it has to be adjusted by hand)

If you go into more detail, in some specific modes of the normal law (like ground, or flare laws IIRC) the lateral control is direct. Also, if you revert to alternate law in flight, direct law will be engaged when the gear is down.
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Starlionblue
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RE: What Is It Like 'hand Flying' An Airbus?

Thu Aug 02, 2012 3:44 pm

Quoting airmagnac (Reply 2):
That's why we abusively talk about FBW or non-FBW, whereas the difference is more on the lines of "lots of sophisticated control laws" vs "a few relatively simple ones"

This is a big misunderstanding about FBW. FBW does not imply envelope protection or vice versa.

I like to define things roughly like this:


-Fly by wire. A means by which control surfaces are signaled with electrical impulses as opposed to wires and pulleys. Examples: F-16, 777, 330/340.

- Computer controlled flight. A means by which a computer controls the flight path. This is completely independent from fly by wire. Nothing stops a computer from controlling an aircraft with cables and pulley. In fact it happens every day in aircraft like the 747-400, where the autopilot controls the surfaces. Example: Any aircraft with an autopilot.

- "Computer interpreted flight" . A means by which computers not only control the surfaces during automated flight, but also interpret pilot commands. In this case, for example, a roll command is not sent directly to the surfaces, but stick side deflection is interpreted as a "desire" by the pilot to roll, and the surfaces are deflected in order to roll the plane in compliance with pilot desire. Surface deflection is not necessarily in proportion to stick deflection. Example: F-16, 330/340.

- Envelope protection. A further development on "computer interpreted flight" by which the computers not only interpret commands but protect the aircraft from commands that may damage it or create an unsafe condition like a stall. Example: 330/340.
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smittyone
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RE: What Is It Like 'hand Flying' An Airbus?

Thu Aug 02, 2012 4:25 pm

Quoting airmagnac (Reply 2):
Correction : you would have to do for yourself with a traditional mechanical linkage flight control design .
The critical difference is not in the cockpit design (yoke or stick), but in what is between it and the control surfaces.
A Boeing 777 or 787 or any other FBW aircraft will behave in approximately the same way, except that you have to trim for speed variations on the 7x7s.

I think I understand this, but help me out with a couple of examples here:

Say the pilot wants to keep the wings level (no roll rate). But wind or thermal effects raise one of the wings, rolling the aircraft slightly. As I understand the Airbus FBW, the computer would immediately roll the wings back to level without pilot input. On the other hand, the pilot of the Boeing FBW would have to physically move the yoke to roll the aircraft back to wings level (if he/she doesn't want to wait for the aircraft's designed-in stability to settle it out)...true?

I understand how conventional pitch trim works...in the sense that if you reduce power in a Cessna etc. the nose will drop to maintain the 'trimmed' speed and the aircraft will descend. Is this how it works on the Boeing FBW? In other words if I have a 777 trimmed to fly level at 200KTS and reduce thrust, will the nose drop and the aircraft descend in order to keep flying at 200KTS?

On the other hand, if I am flying level at 200KTS in an Airbus and then reduce power, will the nose drop and aircraft descend to maintain 200KTS or will it hold the commanded pitch angle while allowing speed to decay?

[Edited 2012-08-02 09:54:53]
 
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airmagnac
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RE: What Is It Like 'hand Flying' An Airbus?

Thu Aug 02, 2012 5:06 pm

Quoting Smittyone (Reply 4):
But wind or thermal effects raise one of the wings, rolling the aircraft slightly. With the Airbus FBW, the computer would immediately roll the wings back to level without pilot input - true?

Yes, but I wouldn't say "immediately" in general. The dynamics will depend on the situation.

Quoting Smittyone (Reply 4):
the pilot of the Boeing FBW would have to physically move the yoke to roll the aircraft back to wings level

No
In lateral, Boeing FBW is just like any other FBW. It will cancel out undesired movements on its own.

The difference is in longitudinal control. To keep the "usual airplane feeling", Boeing introduced a special control law to mimic the usual speed stability that you describe. Or as you say :

Quoting Smittyone (Reply 4):
if I have a 777 trimmed to fly level at 200KTS and reduce thrust, will the nose drop and the aircraft descend in order to keep flying at 200KTS?

=> Yes

However

Quoting Smittyone (Reply 4):
if I am flying level at 200KTS in an Airbus and then reduce power, will the nose drop and aircraft descend to maintain 200KTS or will it hold the commanded pitch angle while allowing speed to decay?

It will hold the load factor, and allow speed to vary freely. In the case it decays, then AOA will be increased to hold the load factor, but eventually it will reach the stalling point. That is a reason why an Airbus needs hard limits.


Speaking of which :

Quoting Starlionblue (Reply 3):
This is a big misunderstanding about FBW. FBW does not imply envelope protection or vice versa.

I did not have envelope protections in mind there, even though I agree with you. My point was that "FBW" in a litteral sense relates to the physical way to transmit information to the control surfaces. But when talking about FBW we are often actually bundling several separate, abstract functions together :
- the control laws, which convert (translate) pilot inputs into surface deflection angles.
- envelope protections
The reason why we mix the terms is that both these functions are so much easier to implement when information is moving around electrically (and even more so if the electrical info is digitally coded as 0s and 1s)
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tdscanuck
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RE: What Is It Like 'hand Flying' An Airbus?

Thu Aug 02, 2012 5:14 pm

Quoting Smittyone (Reply 4):
Say the pilot wants to keep the wings level (no roll rate). But wind or thermal effects raise one of the wings, rolling the aircraft slightly. As I understand the Airbus FBW, the computer would immediately roll the wings back to level without pilot input. On the other hand, the pilot of the Boeing FBW would have to physically move the yoke to roll the aircraft back to wings level (if he/she doesn't want to wait for the aircraft's designed-in stability to settle it out)...true?

No. Airbus and Boeing (now) both control roll rate. If you get an upset in roll the computer will stop the upset (get zero roll rate) but won't go back to level unless the pilot tells it to.

A 777 would need a yoke input to even stop the upset; it has a different lateral/directional control law than a 787. The 777 in roll is a good example of FBW without a (relatively) complex control law.

A 787 controls roll rate (like an Airbus) so it will always try to stop any uncommanded roll.

Quoting Smittyone (Reply 4):
I understand how conventional pitch trim works...in the sense that if you reduce power in a Cessna etc. the nose will drop to maintain the 'trimmed' speed and the aircraft will descend. Is this how it works on the Boeing FBW?

Yes. The 777 and 787 use very similar pitch laws.

Quoting Smittyone (Reply 4):
In other words if I have a 777 trimmed to fly level at 200KTS and reduce thrust, will the nose drop and the aircraft descend in order to keep flying at 200KTS?

Yes.

Quoting airmagnac (Reply 5):
In lateral, Boeing FBW is just like any other FBW.

No. Although they fly similarly, the 777 and 787 use very different lateral control laws.

Tom.
 
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RE: What Is It Like 'hand Flying' An Airbus?

Thu Aug 02, 2012 5:24 pm

Quoting airmagnac (Reply 5):
It will hold the load factor, and allow speed to vary freely. In the case it decays, then AOA will be increased to hold the load factor, but eventually it will reach the stalling point. That is a reason why an Airbus needs hard limits.

Interesting...so when controlling an Airbus in the pitch dimension, it is quite a bit different from the less complex, non-FBW aircraft that pilots "grow up" with. It's like they've decoupled speed from pitch. I guess I can see why Boeing intentionally programmed their FBW to mimic what pilots are accustomed to. Is the Airbus system difficult to get used to?

Quoting tdscanuck (Reply 6):
No. Airbus and Boeing (now) both control roll rate. If you get an upset in roll the computer will stop the upset (get zero roll rate) but won't go back to level unless the pilot tells it to.

So even with roll controls in place there's still work for the pilot to do!
 
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DocLightning
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RE: What Is It Like 'hand Flying' An Airbus?

Thu Aug 02, 2012 6:18 pm

I have a question that is tangential to this topic:

There are a lot of Boeing fanboys who claim that Airbus's envelope protection overrides the pilot's final authority and could be dangerous.

Has there ever been an accident or serious incident in which envelope protection was implicated as a primary or secondary cause or a contributing factor?

*disclaimer: I am a reformed Boeing fanboy, now having a healthy respect and disrespect for both A and B.
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tom355uk
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RE: What Is It Like 'hand Flying' An Airbus?

Thu Aug 02, 2012 6:54 pm

Quoting DocLightning (Reply 8):

Not as far as I am aware. I'd be willing to bet my house (if I owned one, crummy global recession) that envelope protections have saved far more lives than they have cost.
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RE: What Is It Like 'hand Flying' An Airbus?

Thu Aug 02, 2012 8:01 pm

Quoting DocLightning (Reply 8):
Has there ever been an accident or serious incident in which envelope protection was implicated as a primary or secondary cause or a contributing factor?

On a related note, I've asked several times over several years here if an accident involving a Boeing, MD or other type of airliner was ever avoided by banking more than 67o, stalling or in any way busting the limits that the Airbus protections would have prevented. All I've seen so far are suggestions that it might happen one day.
 
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RE: What Is It Like 'hand Flying' An Airbus?

Thu Aug 02, 2012 9:01 pm

Quoting DocLightning (Reply 8):
Has there ever been an accident or serious incident in which envelope protection was implicated as a primary or secondary cause or a contributing factor?

Not that I'm aware of. The only thing I can think of are some near-misses that, (very) arguably, might have not been "near" if envelope protection had been involved. As far as I know, this line of reasoning has only ever been invoked for mid-air collisions.

Tom.
 
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RE: What Is It Like 'hand Flying' An Airbus?

Thu Aug 02, 2012 9:22 pm

Quoting DocLightning (Reply 8):
Has there ever been an accident or serious incident in which envelope protection was implicated as a primary or secondary cause or a contributing factor?

The incident always cited by FBW critics is the A320 on June 28, 1988 at Mulhouse-Habsheim, LFGB, where the A320 flew spectacularly into the trees after a low pass over the runway.

When folks cite that crash as an example - they ignore the facts and the physics.

1) After the plane got so low and slow - it was going to crash. Period. It did not have enough speed, energy, thrust to climb out of the situation the pilot put the plane into.

2) The Envelope Protection did keep the pilot from standing the plane on its tail and causing it to stall and roll and pitch over to hit the ground inverted or at a sharp angle. Rather than losing a few people in the level descent into terrain, without EP it is likely most of the people on the plane would have perished and the survivors horribly burned.


The argument is that some believe a pilot could manually fly the aircraft closer to the edge of a stall than a computer. I'm in the group which believes the computer can do a better job. A pilot might be able to get closer to the edge, but a pilot is also more likely to cross the boundary.
 
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airmagnac
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RE: What Is It Like 'hand Flying' An Airbus?

Thu Aug 02, 2012 9:24 pm

Quoting tdscanuck (Reply 6):
Quoting airmagnac (Reply 5):
In lateral, Boeing FBW is just like any other FBW.

No. Although they fly similarly, the 777 and 787 use very different lateral control laws.

Tom.

Ouch, mixed up several architectures there, thanks for correcting me Tom, I feel like an i****t. Sorry everyone.
Note to self : avoid posting in a hurry before leaving to the cinema with girlfriend  
Hoping to get it right this time : the 777 lateral law is rather "conventional" (apart from the integration into a single set of computers of associated functions such as gust alleviation, yaw dampening, and protections) whereas the 787 introduces the roll rate/sideslip-angle commands ?



BTW on the subject of lateral laws, here is a nice illustration that I wanted to post earlier :
http://www.youtube.com/watch?v=VdhEc07mB9Q

Watch the ailerons move all over the place, it's quite fascinating. The A380 has 2x three ailerons ; when calculating the deflection angle for each one, the flight control computers add a scheduling to dampen some wing structural modes
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imiakhtar
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RE: What Is It Like 'hand Flying' An Airbus?

Thu Aug 02, 2012 9:29 pm

Quoting tom355uk (Reply 9):
Not as far as I am aware.
Quoting tdscanuck (Reply 11):
Not that I'm aware of.

Incorrect. There was an incident involving an IB A320 whereby the protections activated and prevented the aircraft from raising the nose during a go-around attempt in gusty conditions. Aircraft suffered a nose gear collapse and was written off (5G landing). I can't find the report online but I do have it on my hard drive. PM me for a copy.
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RE: What Is It Like 'hand Flying' An Airbus?

Thu Aug 02, 2012 9:44 pm

Quoting imiakhtar (Reply 14):
Quoting tom355uk (Reply 9):
Not as far as I am aware.
Quoting tdscanuck (Reply 11):
Not that I'm aware of.

Incorrect. There was an incident involving an IB A320 whereby the protections activated and prevented the aircraft from raising the nose during a go-around attempt in gusty conditions. Aircraft suffered a nose gear collapse and was written off (5G landing). I can't find the report online

Summary here:
http://aviation-safety.net/database/record.php?id=20010207-0
 
tom355uk
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RE: What Is It Like 'hand Flying' An Airbus?

Thu Aug 02, 2012 9:56 pm

I'll be honest, I hadn't heard of that incident until now, so thanks for that.

However, the key question is this:

"Would the incident have had a less desirable outcome had the envelope protections not been available?"

For example, an aggressive full elevator up deflection in such a low energy state may have actually resulted in a full stall and ended up as a broken wreck on the runway?
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zeke
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RE: What Is It Like 'hand Flying' An Airbus?

Thu Aug 02, 2012 10:36 pm

Quoting Starlionblue (Reply 1):
However I don't know if any FBW Airbus has ever gone into Direct Law in line operation.

I have, lots have. A number of failures where you are in alternate law will give you direct law on gear extension.

Quoting Starlionblue (Reply 1):
There is also a "Mechanical Backup" law even "lower" than Direct Law, where all you have is stabilizer trim and rudder.

Mechanics back is just replacing the electrical lines between the cockpit and the hydraulics, it is not moving the the actual flight controls.

Quoting airmagnac (Reply 5):
It will hold the load factor, and allow speed to vary freely. In the case it decays, then AOA will be increased to hold the load factor, but eventually it will reach the stalling point. That is a reason why an Airbus needs hard limits.

That is not correct, one would never be able to do an emergency descent. If you have a selected speed, and auto thrust off, reduce the thrust back to idle, the elevator will maintain whatever speed in selected.

Quoting DocLightning (Reply 8):

Has there ever been an accident or serious incident in which envelope protection was implicated as a primary or secondary cause or a contributing factor?

I do not think so.

Quoting rfields5421 (Reply 12):

The argument is that some believe a pilot could manually fly the aircraft closer to the edge of a stall than a computer. I'm in the group which believes the computer can do a better job. A pilot might be able to get closer to the edge, but a pilot is also more likely to cross the boundary.

It is the environmental factors which are unknown, computers are quicker at picking up those trends.

Quoting imiakhtar (Reply 14):
There was an incident involving an IB A320 whereby the protections activated and prevented the aircraft from raising the nose during a go-around attempt in gusty conditions. Aircraft suffered a nose gear collapse and was written off (5G landing).

I would have thought the primary cause there was not flying a go-around with the correct technique, the protections prevented the aircraft from stalling. Lowering the nose probably reduced the rate of descent protecting the crew and passengers.

AoA sensors are not immune from environmental turbulence, regardless of what they feed into. On a Boeing, exceeding the sensed AoA would result in stick shaker, and nose down bias, in both cases the sensor is telling the aircraft is it about to stall. The aircraft flight control system does not know it is just about a runway, it is behaving like it is at 1000 ft.

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redflyer
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RE: What Is It Like 'hand Flying' An Airbus?

Thu Aug 02, 2012 10:54 pm

Quoting David L (Reply 10):
On a related note, I've asked several times over several years here if an accident involving a Boeing, MD or other type of airliner was ever avoided by banking more than 67o, stalling or in any way busting the limits that the Airbus protections would have prevented. All I've seen so far are suggestions that it might happen one day.

Haven't there been some incidences where the plane ended up in an upset and the pilots recovered it with some actions that might not have been possible in an EP system, with damage occurring to the airframe? The infamous TWA 727 comes to mind, whereby the pilots decided to finger-f**k the flap system in cruise flight, resulting in a departure from controlled flight. They were able to recover the aircraft before kissing the ground, but not before they had pulled some wild recovery maneuvers, including deploying the landing gear at near Mach 1 speeds. I don't think an EP system would have allowed that. On the other hand - and before anyone mugs me for this example - an EP equipped aircraft would never have allowed the pilots to engage the flaps at cruise to begin with.  
Quoting airmagnac (Reply 13):
BTW on the subject of lateral laws, here is a nice illustration that I wanted to post earlier :
http://www.youtube.com/watch?v=VdhEc...7mB9Q

Great video and pretty amazing how those ailerons work.

Now, if only people would let the rest of us airplane fans just listen to the sound of the engines instead of forcing us to listen to their favorite songs during these aerial demonstration videos then we would all get along.

[Edited 2012-08-02 16:04:51]
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zeke
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RE: What Is It Like 'hand Flying' An Airbus?

Fri Aug 03, 2012 12:09 am

Quoting redflyer (Reply 18):
They were able to recover the aircraft before kissing the ground, but not before they had pulled some wild recovery maneuvers, including deploying the landing gear at near Mach 1 speeds. I don't think an EP system would have allowed that.

The FBW + protections would have stopped the upset to start with, one of the advantages of FBW+protections is the ability for the aircraft to use any combination of flight controls to get the desired flight path. Prevention is better than the cure. One is not restricted to aileron in roll for example. Similar with China Airlines 006, that would not have happened in a FBW aircraft with protections.

If an Airbus does get in an extreme upset, the protections are basically removed, the aircraft is back in direct law. It will remain in normal law if it can, it will provide the best recovery load protection for the airframe.

Quoting redflyer (Reply 18):
On the other hand - and before anyone mugs me for this example - an EP equipped aircraft would never have allowed the pilots to engage the flaps at cruise to begin with.

Nothing stopping you putting flaps out above 20,000 ft.
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Starlionblue
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RE: What Is It Like 'hand Flying' An Airbus?

Fri Aug 03, 2012 12:40 am

Quoting airmagnac (Reply 5):
Quoting Starlionblue (Reply 3):
This is a big misunderstanding about FBW. FBW does not imply envelope protection or vice versa.

I did not have envelope protections in mind there, even though I agree with you. My point was that "FBW" in a litteral sense relates to the physical way to transmit information to the control surfaces. But when talking about FBW we are often actually bundling several separate, abstract functions together :
- the control laws, which convert (translate) pilot inputs into surface deflection angles.
- envelope protections

Sorry airmagnac. On re-reading I realize my answer sounds like I might disagree with you. But I do agree with you!

Quoting imiakhtar (Reply 14):
here was an incident involving an IB A320 whereby the protections activated and prevented the aircraft from raising the nose during a go-around attempt in gusty conditions. Aircraft suffered a nose gear collapse and was written off (5G landing)
Quoting Viscount724 (Reply 15):
Summary here:
http://aviation-safety.net/database/...207-0

Interesting. There's a note at the end of that page about a change to the software following the incident.

Quoting redflyer (Reply 18):
Now, if only people would let the rest of us airplane fans just listen to the sound of the engines instead of forcing us to listen to their favorite songs during these aerial demonstration videos then we would all get along.

  
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tdscanuck
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RE: What Is It Like 'hand Flying' An Airbus?

Fri Aug 03, 2012 1:15 am

Quoting airmagnac (Reply 13):
Hoping to get it right this time : the 777 lateral law is rather "conventional" (apart from the integration into a single set of computers of associated functions such as gust alleviation, yaw dampening, and protections) whereas the 787 introduces the roll rate/sideslip-angle commands ?

Dead on. The 777 lateral control, although FBW (with a pair of cable-controlled spoilers as final backup), is very conventional in that yoke deflection = aileron deflection (with some speed scheduling like any other Boeing). The 787 lateral control law is a combined roll rate/sideslip angle law (called p-Beta...p is roll rate, Beta is sideslip angle).

Quoting imiakhtar (Reply 14):

Quoting tdscanuck (Reply 11):
Not that I'm aware of.

Incorrect. There was an incident involving an IB A320 whereby the protections activated and prevented the aircraft from raising the nose during a go-around attempt in gusty conditions.

I wasn't aware of that event. So, technically, correct! But for the wrong reasons. Interesting case though, I'm curious what would have happened without the protection.

Quoting zeke (Reply 19):
Quoting redflyer (Reply 18):
On the other hand - and before anyone mugs me for this example - an EP equipped aircraft would never have allowed the pilots to engage the flaps at cruise to begin with.

Nothing stopping you putting flaps out above 20,000 ft.

Not sure about Airbus, but Boeing locks out the flaps above FL200.

Tom.
 
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zeke
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RE: What Is It Like 'hand Flying' An Airbus?

Fri Aug 03, 2012 1:26 am

Quoting tdscanuck (Reply 21):
Not sure about Airbus, but Boeing locks out the flaps above FL200.

FL200 is the limit, but nothing to stop you from deploying them. Just excess speed will stop gear or flap deployment.
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RE: What Is It Like 'hand Flying' An Airbus?

Fri Aug 03, 2012 2:40 am

Quoting DocLightning (Reply 8):
There are a lot of Boeing fanboys who claim that Airbus's envelope protection overrides the pilot's final authority and could be dangerous.

Actually A and B envelope protections are so similar that it is trivial.

B planes say: I protest because if you pull any harder you break off the wings. A planes say: You are about to break off the wings, I'm not going to do that.

B says: I protest because if you roll any harder you are asking me for a spiral dive which eventually will break off the wings. (If, however, you are at an air show and want to demonstrate a barrel roll, please go ahead). A says: You tell me to enter a spiral dive, which eventually will break off the wings. I will give you the maximum roll rate which will prevent a spiral dive at maximum wing load, and therefore prevent breaking off the wings.

B says: I protest because if you pull any harder, we will stall, and you will be in one hell of a mess. A says: You ask me for a stall. You must be crazy, I'm going to the limit for helping you, but you are already in a mess and I refuse to make it even worse for you.

Etc...

Could the envelope protections be more similar without being totally identical?

There are significant differences in the ordinary control philosophies between A and B, but exactly envelope protection differences are trivial. And BTW, 99+% of all A and B drivers should hopefully reach retirement age without ever getting close to the envelope limits. Except in the sims, of course.
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spink
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RE: What Is It Like 'hand Flying' An Airbus?

Fri Aug 03, 2012 6:49 am

Quoting DocLightning (Reply 8):
Has there ever been an accident or serious incident in which envelope protection was implicated as a primary or secondary cause or a contributing factor?

I'm sure that has been at least one, though in theory it would be because of incorrect software/bug. The other side of the situation that a pilot has to be aware of is to not be too dependent on the EP that in case of failure, etc, where the EP isn't available that you mistakenly rely on it. This is something that can only really be handled through repeated continuous training and is something that you have to be aware of with any system that normally tries to prevent you from doing bad things.
 
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airmagnac
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RE: What Is It Like 'hand Flying' An Airbus?

Fri Aug 03, 2012 8:32 am

Quoting Starlionblue (Reply 20):
Sorry airmagnac. On re-reading I realize my answer sounds like I might disagree with you. But I do agree with you!

No problem, if we both agree !   

Quoting zeke (Reply 17):
Quoting airmagnac (Reply 5):
It will hold the load factor, and allow speed to vary freely. In the case it decays, then AOA will be increased to hold the load factor, but eventually it will reach the stalling point. That is a reason why an Airbus needs hard limits.

That is not correct, one would never be able to do an emergency descent. If you have a selected speed, and auto thrust off, reduce the thrust back to idle, the elevator will maintain whatever speed in selected.

I've been burned once already with that post, and you have much more expertise than I do, so please don't hesitate to bring out the flame thrower !
But to clarify, the topic was about "hand flying", which I interpret as AP OFF/ATHR OFF, and giving commands through the sidestick. IOW, considering ATA27 flight control laws only.

If you're talking about selected speed, then that would mean AP is on and calculating the proper Nz commands to follow your selected speed.
So you've added the autoflight system in the mix, which will be updating the Nz command input to the flight control laws. Whereas I was considering a constant Nz input (stick neutral). IOW we're talking about different things.

For your emergency descent case, supposing throttle is constant at idle, AP&ATHR OFF and considering longitudinal commands only. If you push forward on the stick, you request a load factor decrease, the nose goes down, then you release the stick. You will be established in a descent, and depending on the flight path angle (and thrust variation with altitude), speed will vary. It may stabilise at some point within the acceptable range, but it may also go past MMO, at which point the overspeed protection will kick in.
At least that's how I see things, I'm puzzled as to why you say an emergency descent would not be possible ?
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David L
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RE: What Is It Like 'hand Flying' An Airbus?

Fri Aug 03, 2012 10:55 am

Quoting imiakhtar (Reply 14):
There was an incident involving an IB A320 whereby the protections activated and prevented the aircraft from raising the nose during a go-around attempt in gusty conditions.

There's a bit more perspective here:

http://www.iasa.com.au/folders/Safety_Issues/others/Bilbao.html

It seems to me that there was more involved than simply gusty conditions and Alpha protection. Dual input caused by what may have been an "iffy" transfer of control can't have helped either. From the article:

"The airport is dreaded by pilots for its critical conditions, - especially in the winter, and is not equipped with improved weather measuring equipment or modern windshear detectors. The airport was the scene of two other weather related accidents that occurred during the preceding 15 days and another three in the previous five months.

Bilbao’s Air Traffic Control did not mention to the Iberia crew that, just shortly before the A320's approach, three other aircraft had tried unsuccessfully to land at Sondica and had finally decided to divert. According to statements of airport personnel to local media after the event, other flights also diverted directly to their alternate, without even trying to land in Bilbao. "


Quoting redflyer (Reply 18):
The infamous TWA 727 comes to mind, whereby the pilots decided to finger-f**k the flap system in cruise flight, resulting in a departure from controlled flight.

Was that the one where they decided to extend the slats at cruise to see if it reduced the fuel burn? And didn't it involve pulling a CB or something along those lines?
 
tdscanuck
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RE: What Is It Like 'hand Flying' An Airbus?

Fri Aug 03, 2012 12:14 pm

Quoting zeke (Reply 22):
Quoting tdscanuck (Reply 21):
Not sure about Airbus, but Boeing locks out the flaps above FL200.

FL200 is the limit, but nothing to stop you from deploying them.

Ah, ok. Same limitation, different implementation. On a modern Boeing, if you move the flap handle above FL200 nothing will happen.

Quoting David L (Reply 26):
Quoting redflyer (Reply 18):
The infamous TWA 727 comes to mind, whereby the pilots decided to finger-f**k the flap system in cruise flight, resulting in a departure from controlled flight.

Was that the one where they decided to extend the slats at cruise to see if it reduced the fuel burn? And didn't it involve pulling a CB or something along those lines?

I believe they were playing with the flaps (there is some justification, in theory, since cruise flap adjustment is actually implemented on the newest airliners today). They opened the slat CB to keep the slats in place. The FE was either out of the loop or absent. When the FE saw the open CB he reset it, causing the slats to extend at cruise.

Tom.
 
David L
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RE: What Is It Like 'hand Flying' An Airbus?

Fri Aug 03, 2012 12:43 pm

Quoting tdscanuck (Reply 27):
I believe they were playing with the flaps (there is some justification, in theory, since cruise flap adjustment is actually implemented on the newest airliners today). They opened the slat CB to keep the slats in place.

D'oh. Of course... flaps without slats. That's why the CB had to be pulled.   
 
RickNRoll
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RE: What Is It Like 'hand Flying' An Airbus?

Wed Aug 08, 2012 2:50 am

Quoting tom355uk (Reply 16):
For example, an aggressive full elevator up deflection in such a low energy state may have actually resulted in a full stall and ended up as a broken wreck on the runway?

Much like the A320 crash, no point letting a pilot attempting to pull up if the computer has worked out that all you will do is stall if it lets you. The 'controlled', low speed crash was probably the better alternative.
 
Pihero
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RE: What Is It Like 'hand Flying' An Airbus?

Wed Aug 08, 2012 5:45 pm

Quoting airmagnac (Reply 5):
Quoting Smittyone (Reply 4):if I am flying level at 200KTS in an Airbus and then reduce power, will the nose drop and aircraft descend to maintain 200KTS or will it hold the commanded pitch angle while allowing speed to decay?
It will hold the load factor, and allow speed to vary freely. In the case it decays, then AOA will be increased to hold the load factor, but eventually it will reach the stalling point. That is a reason why an Airbus needs hard limits.

That's quite incorrect.
If you handfly level and pull the T/L to idle two thinghs will happenn in succession :
1/- The "Pitch Normal Law " will keep ther flight level and the auto trim will come in .
2/- At Vls, the pîlot mpust react. ... If not, the deceleration willo continue to the limit of the auto trim... That will be the Alpha Prot Aoa, which will be kept as the airplane will begin to descend, i.e the descent will be done at Alpha Prot.
From that moment on, the Flight Control System will allow the pilot to increase the AoA to Alpha Max. The forward stick control is of course not affected.
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Jetlagged
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RE: What Is It Like 'hand Flying' An Airbus?

Thu Aug 09, 2012 12:08 pm

Quoting Smittyone (Thread starter):
I'm just curious to hear from Airbus pilots - what is it like to fly with the side stick? Is it easier or harder than a conventional yoke? Does the computer system take up some of the workload of keeping the wings level or maintaining a desired pitch angle that you would have to do for yourself with a Boeing's yoke and trim controls?

I'm not an Airbus pilot, but I have flown A320 full flight simulators on many occasions, as well as conventional and FBW Boeings. The Airbus sidestick feels very natural to use. It's heavily spring loaded and damped, nothing like a gaming joystick for example. The aircraft basically goes where you point it, so hand flying is a pleasant and rewarding experience for a novice like me. Perhaps pilots with many thousands of hours may miss the finesse required to fly more conventional aircraft as smoothly. Flying normally (small inputs, no excessive attitude) you don't get anywhere near the protections so the only noticeable difference is that when changing configuration the FBW smooths things out more.
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Pihero
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RE: What Is It Like 'hand Flying' An Airbus?

Fri Aug 10, 2012 1:40 pm

Now to answere nthyen OP.

Quoting Smittyone (Thread starter):
what is it like to fly with the side stick?

An incredible precision of piloting. It's surprisingly easy tto adapt to the sidestick... It feels natural after five minutes. What takes longer is not to have a big control column between one's legs - One feels quite vulnerable  .

Quoting Smittyone (Thread starter):
Does the computer system take up some of the workload of keeping the wings level or maintaining a desired pitch angle that you would have to do for yourself with a Boeing's yoke and trim controls?

The aircraft is always in trim, so one is rid of that part of handflying.
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smittyone
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RE: What Is It Like 'hand Flying' An Airbus?

Sat Aug 11, 2012 12:56 am

Thanks for all the thoughtful replies, very interesting stuff.

Pihero, do you think it would be hard for you to go back to the old school column/trim setup now?
 
Pihero
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RE: What Is It Like 'hand Flying' An Airbus?

Sun Aug 12, 2012 7:35 pm

Quoting Smittyone (Reply 33):
Pihero, do you think it would be hard for you to go back to the old school column/trim setup now?

First of all, I wouldn't want to - I've been assimilated by the 'Bus Borgs !
Two remarks, though :
1/- Quite a lot of my colleagues flew the 320, then went on the T7 and subsequently the 380... without any problem at all.
2/- Contrarily to what people think, the hand movement doesn't change that mucuch between flying the 'Bus or any other aircraft : See for instance the shape of a Tristar yoke and yoiu'll understand that the movement of the hand is similar.
What we won't have any more on the 'Airbii' is the opportunity to use the inside hand for piloting - and for what ?.
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mandala499
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RE: What Is It Like 'hand Flying' An Airbus?

Mon Aug 13, 2012 10:06 am

Quoting airmagnac (Reply 2):
Same as above : if you are in the stick's neutral position for pitch, you are telling the plane to hold its current attitude. (it's slightly more complicated because the input is actually a blend of pitch rate and load factor, but the general idea is the same)
Quoting airmagnac (Reply 5):
It will hold the load factor, and allow speed to vary freely. In the case it decays, then AOA will be increased to hold the load factor, but eventually it will reach the stalling point. That is a reason why an Airbus needs hard limits.

It will hold load factor, and speed AND pitch will vary to maintain that load factor.

Quoting Smittyone (Reply 7):
It's like they've decoupled speed from pitch. I guess I can see why Boeing intentionally programmed their FBW to mimic what pilots are accustomed to. Is the Airbus system difficult to get used to?

Use a Boeing CWS... it'll hold pitch and roll if you leave the yoke alone...   

Quoting Pihero (Reply 34):
1/- Quite a lot of my colleagues flew the 320, then went on the T7 and subsequently the 380... without any problem at all.

LOL! A lot of others have been through that process... but the other way around too. 737 then to 330 then back to 737 then to 777 or 330... or 737 then to 777 then to 737 then to 330... No problems.
However, I know one case here where one captain who recently completed his 320 training and had just passed his 320 line check ride, volunteered to fly back on the 737, and since his 737 rating was still current, he went back through a short ground course and then went to the sim before they let him back in the air on the 737... he failed miserably in trim and TO/GA activation. He dumped the course and went back to the 320... mind you, that scheme was immediately changed by doing a longer ground course for those needed to fly the 737, and the type's retirement was postponed to allow 6 months to 12 months before the guys transitioned back to 320. Those who had the longer course, had no problems... retention was reduced to negligeable risk.

Mandala499
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