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kimon
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A320 Mode Glitch?

Mon Mar 08, 2010 6:07 am



Quote:
German investigators believe Airbus should assess aspects of A320 flight logic after determining that partial loss of lateral control authority contributed to the Lufthansa wing-strike in Hamburg two years ago.
http://www.flightglobal.com/articles...be-queries-a320-landing-logic.html

[Edited 2010-03-09 03:36:48 by EI787]
 
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Starlionblue
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RE: A320 Mode Glitch?

Mon Mar 08, 2010 7:51 am

Well, that's interesting. Still, I wouldn't call ONE event non-fatal event in 25 years of service a big design issue.

Also, it could probably be argued that they should not have put themselves in such a situation in the first place. But I guess it is hard to know about the exact gusts until you're there, if you will.
 
kimon
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RE: A320 Mode Glitch?

Mon Mar 08, 2010 10:31 am

Indeed!Must have been one hell of a gust!
BTW,are there limits on windy landings?
Are aircraft barred from landing in crazy wind?
What are the regs and rules?
For T/O no problem if crazy windy?
Many thanks!
 
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Starlionblue
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RE: A320 Mode Glitch?

Mon Mar 08, 2010 11:50 am

Quoting kimon (Reply 2):
BTW,are there limits on windy landings?

Of course.

Quoting kimon (Reply 2):
Are aircraft barred from landing in crazy wind?

If we define "crazy" as "beyond regulatory and operator limits" then yes, they are barred.

Quoting kimon (Reply 2):
For T/O no problem if crazy windy?

There are limits here too.
 
Fabo
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RE: A320 Mode Glitch?

Mon Mar 08, 2010 2:13 pm

Depends. You will have limits on tailwind, and headwind, by many times, you wont have limit crosswind, only maximal demonstrated. Then there are other problems, with this issue, discussed in full BFU report. One of the finding is, that this topic needs to be more precisely worded and defined.
 
tdscanuck
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RE: A320 Mode Glitch?

Tue Mar 09, 2010 4:45 am

I'm not sure this is an avoidable problem...air/ground transition in control laws is a very thorny topic on a good day, mostly because the aircraft itself doesn't go from air to ground in a binary fashion. Unless you plunk a perfect three-point landing, you're always going to be in some situation where part of the plane is in "ground mode" and part is in "air mode" and the flight controls can't do both at once. For ever situation like this one where staying in air mode could have helped, I'm sure we could think up one where it stayed in air mode when going to ground mode would have helped.

At the end of the day...stabilize your approach, don't bounce your landing, and if it all goes to !#%!, go around (which is exactly what this crew did).

Tom.
 
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Starlionblue
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RE: A320 Mode Glitch?

Tue Mar 09, 2010 5:12 am

I think it was SlamClick who said that landing was a bit like stepping onto a small boat from the pier. On the pier, you're fine. In the boat, you're fine. Getting safely between the two is the trick.
 
DH106
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RE: A320 Mode Glitch?

Tue Mar 09, 2010 11:01 am

Quoting tdscanuck (Reply 5):
I'm not sure this is an avoidable problem...air/ground transition in control laws is a very thorny topic on a good day, mostly because the aircraft itself doesn't go from air to ground in a binary fashion.

Perhaps there could be a transition phase between (say) first wheel touchdown and all 3 wheels down/spoilers deployed, where full roll rate is still permitted, but allowable roll angles are reduced to below the wing tip strike angle.
 
AutothrustBlue
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RE: A320 Mode Glitch?

Tue Mar 09, 2010 3:54 pm

Quoting DH106 (Reply 7):
but allowable roll angles are reduced to below the wing tip strike angle.

Wouldn't this be case where aileron movement is supposed to be halved in order to prevent wingtip strike when the a/c lands on one gear?
 
jayeshrulz
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RE: A320 Mode Glitch?

Tue Mar 09, 2010 4:45 pm

The mode switch was triggered by the brief touchdown of the left main landing-gear during the 1 March 2008 landing. Even though the right main gear did not make contact, the control logic transitioned to 'ground' mode, halving the aileron deflection available through the pilot's sidestick.

Just after the touchdown the aircraft lost contact with the runway, and in the gusting wind conditions banked 23° left. Both pilots reacted with full right sidestick, and up to 14° right rudder, but the limited control authority meant they were unable to counter the bank enough to avoid the wing-tip strike.



What does "halving the aileron deflection available through the pilot's sidestick" mean?

Does A330 and other airbus too have the same glitch?
 
AutothrustBlue
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RE: A320 Mode Glitch?

Tue Mar 09, 2010 6:02 pm

Saw a related article which mentioned wind speeds at the time of landing:

Quote:
German investigation agency BFU, in a final report into the incident today, states that the crew had opted to make the de-crabbed approach after being informed that winds were at 28kt, gusting to 37kt.

Airbus' A320 flight crew operating manual, under the term 'maximum crosswind demonstrated for landing, gives a figure of 33kt gusting to 38kt.

During LH044's final approach, however, the crew was told that the winds were still around 28-29kt but gusting to 47kt.
http://www.flightglobal.com/articles...needed-after-a320-wing-strike.html
 
tdscanuck
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RE: A320 Mode Glitch?

Tue Mar 09, 2010 6:47 pm

Quoting jayeshrulz (Reply 9):
What does "halving the aileron deflection available through the pilot's sidestick" mean?

You've always got a gain between the command device (sidestick, in this case) and surface deflection. The quoted phrase means that a full sidestick deflection would only result in half the aileron deflection that it would have before the mode switch.

Quoting jayeshrulz (Reply 9):
Does A330 and other airbus too have the same glitch?

It's not a glitch, it's how the software is supposed to work. The airplane did exactly what it was supposed to do under the circumstances. The issue is that what the flight crew wanted the airplane to do and what the airplane was capable of doing didn't match...this is, arguably, a design problem but it's not a glitch.

Tom.
 
KELPkid
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RE: A320 Mode Glitch?

Thu Mar 11, 2010 2:18 am

Quoting Starlionblue (Reply 6):
I think it was SlamClick who said that landing was a bit like stepping onto a small boat from the pier. On the pier, you're fine. In the boat, you're fine. Getting safely between the two is the trick.

Not necessarily true, especially in light aircraft. I've had days where you had to fly the plane back to the tiedowns...(40 knot wind straight down the runway at TTD, anyone?   ). On days like that, in a light airplane, if you don't hold crosswind correction all the way back to the tiedowns, the plane could potentially flip over. You are also fighting the plane's tendency to weathervane (point right into the wind) any time you have to turn away from the wind.

I have also had an extreme wind gust (I'm guessing it was part of the downdraft of a thunderstorm, in retrospect) blow so hard on the runway that, despite the fact that I had landed the aircraft and was coming to a stop, the aircraft weathervaned into the wind and ended up in the dirt  Wow! (fortunately, no damage beyond egos...).
 
PGNCS
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RE: A320 Mode Glitch?

Thu Mar 11, 2010 10:28 pm

Quoting tdscanuck (Reply 11):
Quoting jayeshrulz (Reply 9):
Does A330 and other airbus too have the same glitch?

It's not a glitch, it's how the software is supposed to work. The airplane did exactly what it was supposed to do under the circumstances. The issue is that what the flight crew wanted the airplane to do and what the airplane was capable of doing didn't match...this is, arguably, a design problem but it's not a glitch.

Tom's right: it's not a glitch; it was designed that way for a reason, and in many years on the A-320 series it was never a problem for me, anyone I know, or to anyone at my operator to the best of my knowledge. Tom makes a valid point that it is possibly a design issue (from my experience I am dubious), but the question Airbus will have to confront is whether to do anything at all, whether to modify the transition between the two modes by blending them gradually, or revising the availability of aileron deflection on the ground, which may make this particular situation less likely to recur, but greatly exacerbate other problems. In this case the pilots were certainly in a place they shouldn't have been in given the winds they encountered. Before looking at the airplane (which I have every confidence in being able to deal with the winds specified in the FCOM), look at the crew's decision making on this approach.
 
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Starlionblue
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RE: A320 Mode Glitch?

Thu Mar 11, 2010 11:21 pm

This is yet another one of those design compromises. Faced with the lesser of two evils (well, not really but you know what I mean), the Airbus guys decided this was better.

All aircraft have idiosyncrasies.
 
jayeshrulz
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RE: A320 Mode Glitch?

Fri Mar 12, 2010 8:33 am

Quoting PGNCS (Reply 13):

Do ailerons help in ground?
If not, what was the reason for halving it?
Let it be full and normal until and unless it does not interfere with the ground conditions.
 
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Starlionblue
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RE: A320 Mode Glitch?

Fri Mar 12, 2010 9:19 am

Quoting jayeshrulz (Reply 15):
Do ailerons help in ground?

The point is that the aircraft switches to ground mode with only one main on the ground.

Quoting jayeshrulz (Reply 15):
If not, what was the reason for halving it?

My WAG: Ironically, so that you don't command too much roll and hit a wingtip on the ground.

Quoting jayeshrulz (Reply 15):
Let it be full and normal until and unless it does not interfere with the ground conditions.

Airbus has good reasons for halving aileron response in ground mode.
 
PGNCS
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RE: A320 Mode Glitch?

Fri Mar 12, 2010 11:59 pm

Quoting jayeshrulz (Reply 15):
Do ailerons help in ground?

Yes.

Quoting jayeshrulz (Reply 15):
If not, what was the reason for halving it?

It helps prevent overcontrolling the aircraft for one thing. The ailerons on the A-320 are VERY effective, and provide more than enough roll contol in any condition covered within the operational limitations of the aircraft.

Quoting jayeshrulz (Reply 15):
Let it be full and normal until and unless it does not interfere with the ground conditions.

Airbus doesn't make control law decisions arbitrarily, and they have very good reasons for designing the ailerons and their gains they way they did.
 
bri2k1
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RE: A320 Mode Glitch?

Mon Mar 15, 2010 1:58 pm

Quoting Starlionblue (Reply 3):
If we define "crazy" as "beyond regulatory and operator limits" then yes, they are barred.

Quoting kimon (Reply 2):
For T/O no problem if crazy windy?

There are three different kinds of limitations on aircraft operation. In the US at least, adherence to each is required by Federal law.

One is the limits of the crew. If my skills, and perhaps my alertness after a long flight, are only up to a 20-knot crosswind component, then I must be aware of that. I fly under part 91, and 91.103 states, "Each pilot in command shall, before beginning a flight, become familiar with all available information concerning that flight." Part 121 and Part 135 operators have similar statements included in their approved operation manuals. This is a catch-all but it includes knowing the current and forecast winds at the destination and any alternate and knowing if the runways available will lie within my crosswind limits.

Another is the limitations of the airframe. FAR Parts 23 and 25 cover the design requirements for airplanes in the normal and transport categories, but neither says anything about a maximum crosswind. Even the maximum operating airspeed is loosely defined as a function of demonstrated load capabilities on airframe components. It does specify that the airplane must come with operating instructions, and for normal category airplanes, this includes a maximum demonstrated crosswind component. It has very little to do with the capabilities or limitations of the airplane though, and is not considered a limitation. It is usually just the best crosswind that was available on the day the test was performed, and since it was demonstrated, it's included in the operating instructions. It is a piece of information that the pilot must become familiar with, but the crosswind in which a plane might land could be greater or lesser than this number, depending on the other sets of limitations.

The last set of limitations is the kind imposed by law. In the US (and most other places) there is no absolute limit on crosswinds, or any other kind of winds. The legal limitations usually just require adherence to other kinds of limitations, and that means failing to adhere to them becomes a violation of law, not just poor operating practice. The limitations imposed by Part 121/135 operation manuals are almost always far stricter than the generic limitations under the law, although those manuals become enforceable by the same laws.

In summary, the primary limitation is usually the ability of the pilot him or herself to know and understand his or her own capabilities and those of the airplane, and ensure the flight remains within those limits at all times. There are no speed limit signs on the side of the runway indicating the maximum crosswind permitted for landing. I think it could be misleading to say "operation in crazy winds is barred" without any further explanation.

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