LH A320 Rough Landing @ Hamburg
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PBL, I agree with you that the x-wind component of either runway was equal. Their problem was after decrabing unless you keep the bank into the wind you will drift across to the downwind side of the runway. You learn this as a student pilot. Letting the upwind wing come up after decrabing will have very consistent results, going off the downwind side of the runway. She didn't understand how to do a cross wind landing to let that happen. If it was a gust that lifted that wing an experienced pilot would have gone around but it didn't look like a gust.
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I am no doubt going to touch on a previously mentioned and very personal subject to all pilots, so sorry to all whom this offends.
I personally feel this is an advert for a cross control approach setting off the drift early on allowing the PF to assess the x wing comp before 20feet. This probably would of ended in an earlier GA or a more controlled touch down and would be much more comfortable for the pax and crew in the back. I only say this because this is how I have been trained and demonstrated to me.
I personally feel this is an advert for a cross control approach setting off the drift early on allowing the PF to assess the x wing comp before 20feet. This probably would of ended in an earlier GA or a more controlled touch down and would be much more comfortable for the pax and crew in the back. I only say this because this is how I have been trained and demonstrated to me.
Rtfcom 3.04.27!
A320 will always try to correct the uncommanded roll (in normal law, of course).
There is a caveat, though.
The way she tries to do it is nice, easy & smooth. First, it's not the way to fly the airplane in moderate turbulence, second, the inbuilt lag makes legions of busdrivers believe (wrongly) that she doesn't pick up the dropped wing.
Typical encounter with gust that is too much for ELACs and SECs to handle immediately, makes Average Joe Busdriver slam the stick into wind. Bad news is that startled FBW has just started to pick up the wing and now it adds its automatic command to stick request and then plane rolls rapidly into wind, zooming past wings level. Now stick goes to opposite side and nice airplane-pilot coupling in roll ensues - sometimes with the tipical bus sound of stick clackclackclackclackclackclacking against the roll stops. I've seen the guys hitting the stops in 9G14 and I never had to use more than ha'f-a-stick in 17G29. Mind you, in both cases bank was maintained within 5° of wings level. FCOM says pilot should filter his stick inputs. Way I interpret (and do) it is; when the wing drops, I help ELACs by giving approximately half the deflection, but return stick to neutral slightly before wings level. Maybe even this is excessive, but for me works like a charm.
As for rudder: kicking out the drift is too much for FBW to handle but if you squeeze it out, bank will stay constant with stick in neutral.
This is another of A320 quirks, on take-off the rudder has to be briskly moved to neutral as soon as rotation is initiated. In everything except the gustiest of weather, the airplane settles into wind with zero bank and zero stick input as if by magic. First time I've was briefed on this technique, I thought that my instructor was pulling my leg. It turned out that he wasn't and that the thing that lifts the wing is the rudder held too long and not the wind.
There is a caveat, though.
The way she tries to do it is nice, easy & smooth. First, it's not the way to fly the airplane in moderate turbulence, second, the inbuilt lag makes legions of busdrivers believe (wrongly) that she doesn't pick up the dropped wing.
Typical encounter with gust that is too much for ELACs and SECs to handle immediately, makes Average Joe Busdriver slam the stick into wind. Bad news is that startled FBW has just started to pick up the wing and now it adds its automatic command to stick request and then plane rolls rapidly into wind, zooming past wings level. Now stick goes to opposite side and nice airplane-pilot coupling in roll ensues - sometimes with the tipical bus sound of stick clackclackclackclackclackclacking against the roll stops. I've seen the guys hitting the stops in 9G14 and I never had to use more than ha'f-a-stick in 17G29. Mind you, in both cases bank was maintained within 5° of wings level. FCOM says pilot should filter his stick inputs. Way I interpret (and do) it is; when the wing drops, I help ELACs by giving approximately half the deflection, but return stick to neutral slightly before wings level. Maybe even this is excessive, but for me works like a charm.
As for rudder: kicking out the drift is too much for FBW to handle but if you squeeze it out, bank will stay constant with stick in neutral.
On rotation, prior to lift-off, the upwind wing invariably rises, even though the pilot is easing off the usual slight downwind rudder.
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PBL,
Wrong, according to Airbus FCOM the A320 will "Roll Conventionally when
using fast or large rudder inputs" (below).
If it had been a gust, the aircraft would have crashed. At the point
where the wing hit ground, there still was no (or very little) roll input.
This picture proves it;
http://www.airliners.net/uf/53688288.../phpOltUWB.jpg
The acf was saved by the laws of physics.
Cheers,
M
Sorry, as I understand it this does not happen. If sidestick is neutral, wing does not come up due to yaw-roll coupling. The FBW control system compensates for the coupling. (This also answers GMDS's question.)
I think it was a gust.
I think it was a gust.
using fast or large rudder inputs" (below).
If it had been a gust, the aircraft would have crashed. At the point
where the wing hit ground, there still was no (or very little) roll input.
This picture proves it;
http://www.airliners.net/uf/53688288.../phpOltUWB.jpg
The acf was saved by the laws of physics.
Cheers,
M
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OHOH!!!
looks like clear case of copilot behind the airplane and captain behind the copilot; letting your copilot land in gusts to 55kts??? nice safe though, cosidering the wing could have been missing......anyway lufthansa pilots don't do that; it must have been a nasty gust; only everybody else....
Have flown both B737 and A320 and landed both in limiting crosswinds. There is nothing special about landing the A320 in a crosswind compared to the B737.
I dont like the phrase "kicking" off the drift. I have never had an occasion where it was necessary to kick the rudders. I think the phrase "straighten (or align) the a/c with the runway track" is far more appropriate. The further effect of rudder is and always has been roll in any a/c which I have encountered. Therefore as you apply the rudder you need to apply opposite aileron to keep the wings level. If you are going to make any mistakes apply too much aileron rather than not enough.
I dont like the phrase "kicking" off the drift. I have never had an occasion where it was necessary to kick the rudders. I think the phrase "straighten (or align) the a/c with the runway track" is far more appropriate. The further effect of rudder is and always has been roll in any a/c which I have encountered. Therefore as you apply the rudder you need to apply opposite aileron to keep the wings level. If you are going to make any mistakes apply too much aileron rather than not enough.
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Never had a problem landing into max X winds with an Airbus, great aircraft.Flying a Boeing now, great aircarft to. infact no such thing as bad aircraft, I only see bad pilots. The only time I almost landed in the grass in lower than limit X winds in Milan was when ..............I stuffed up.
Don't see anything here than poor aircraft control. Sounds harsh but that's that !
LH PR department had to make them heroes. The in house debrief may have been a tad less enjoyable.
Don't see anything here than poor aircraft control. Sounds harsh but that's that !
LH PR department had to make them heroes. The in house debrief may have been a tad less enjoyable.
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Originally Posted by bubbers44
You learn this as a student pilot. Letting the upwind wing come up after decrabing will have very consistent results, going off the downwind side of the runway.
Originally Posted by bubbers44
She didn't understand how to do a cross wind landing
XPMorten,
you quote me the training manual. Are you trying to say that you believe that when the rudder is moved abruptly, the yaw-roll decoupling rules take a holiday? Or is it more likely that the training manual is saying that abrupt movement of the rudder can be faster than the decoupling? Just as the aircraft's reaction to a gust with stick neutral may well be a roll, despite the control-system compensation.
That wing comes up pretty fast. I don't think it's solely because of yaw-roll coupling. I think there was a gust.
PBL
Last edited by PBL; 7th Mar 2008 at 18:58. Reason: EDDHATC says 50 kts
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Many of the posters on this thread seem a tad too ready to criticise the performance of the LH flight crew for this incident at Hamburg last Saturday. Is it just possible that they encountered a gust of exceptional velocity at the most vulnerable stage of their landing?
I live in Tayside, Scotland and last weekend we experienced wind gusts which I thought were 'unusual' in relation to the mean wind speed. From figures recorded at Perth airfield, the mean wind speed was around 30-35 kts but some of the gusts were exceptionally strong (85 kts) and of short duration (10-15 seconds). If the LH A320 crew were unlucky enough to encounter a sudden gust of similar velocity at Hamburg, it may well have caught them out. It certainly caught out one of my golfing companions last weekend. He was blown flat on his back while hitting one of his tee shots! (PBL: Is it normal for the gust/mean windspeed ratio to be around 3?)
On the 'evidence' presented on this thread, together with the nature of the wind I experienced personally last weekend, I'm inclined to give Maxi J. and her captain the 'benefit of the doubt' on this occasion.
Mariners seem to have a healthy respect for the sea/weather and accept that, just occasionally, mother nature can produce conditions which will overwhelm the largest ships crewed by the finest seamen. Perhaps, aviators should show a similar humility with regard to the capabilities of their aircraft and their prowess as pilots.
I live in Tayside, Scotland and last weekend we experienced wind gusts which I thought were 'unusual' in relation to the mean wind speed. From figures recorded at Perth airfield, the mean wind speed was around 30-35 kts but some of the gusts were exceptionally strong (85 kts) and of short duration (10-15 seconds). If the LH A320 crew were unlucky enough to encounter a sudden gust of similar velocity at Hamburg, it may well have caught them out. It certainly caught out one of my golfing companions last weekend. He was blown flat on his back while hitting one of his tee shots! (PBL: Is it normal for the gust/mean windspeed ratio to be around 3?)
On the 'evidence' presented on this thread, together with the nature of the wind I experienced personally last weekend, I'm inclined to give Maxi J. and her captain the 'benefit of the doubt' on this occasion.
Mariners seem to have a healthy respect for the sea/weather and accept that, just occasionally, mother nature can produce conditions which will overwhelm the largest ships crewed by the finest seamen. Perhaps, aviators should show a similar humility with regard to the capabilities of their aircraft and their prowess as pilots.
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Or is it more likely that the training manual is saying that abrupt movement of the rudder can be faster than the decoupling? Just as the aircraft's reaction to a gust with stick neutral may well be a roll, despite the control-system compensation.
If you think it should say "Roll-unconventionally", you better tell Airbus
to rewrite their manual.
I think there was a gust.
by miracle STOPS 1 second later when the wing hits the ground
so the wing doesnt get ripped off.
M
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Wise words, Avionista.
As to gusts, I think we don't know much about them. There are a bunch of wheatfields around here, and every year as I cycle past, I notice roughly circular areas some 5-10m in diameter *flattened*. Now, that's in normal weather, and I think it would take some 50+kts to break a stalk in the middle of a dense wheat field. There are small, narrow, tornado-like funnels in most normal storms, it seems.
I used to live in an apartment that backed onto a meadow at the end of a long funnel of parks that came down from the hills. The meadow was about 100m wide, and in the middle was a copse of tall conifers, about 20m wide. There was a fair wind storm a few years ago, and after the storm I noticed some areas of flattened grass. The grass stalks were some 1m high at that point. I went to look. On the lee side of the copse was a circle about 2m diameter in which the grass had been completely flattened, in a circular pattern. Everything outside that circle was standing upright. That is, a funnel of unusual strength had grounded exactly there, all 2m of it. 60kt or more, in circular form, and confined to 2m diameter, in a storm of average 30kt or less.
Now, something like that isn't going to disturb an A320, because it is too localised (I once had a dust devil go right over me, and my parked airplane, at the Mammoth Lakes airport in the Sierras. Entertaining, not worrying). But widen it three or four times, as in a serious storm, and you have something that could kip a wing. Or flatten a golfer.
PBL
As to gusts, I think we don't know much about them. There are a bunch of wheatfields around here, and every year as I cycle past, I notice roughly circular areas some 5-10m in diameter *flattened*. Now, that's in normal weather, and I think it would take some 50+kts to break a stalk in the middle of a dense wheat field. There are small, narrow, tornado-like funnels in most normal storms, it seems.
I used to live in an apartment that backed onto a meadow at the end of a long funnel of parks that came down from the hills. The meadow was about 100m wide, and in the middle was a copse of tall conifers, about 20m wide. There was a fair wind storm a few years ago, and after the storm I noticed some areas of flattened grass. The grass stalks were some 1m high at that point. I went to look. On the lee side of the copse was a circle about 2m diameter in which the grass had been completely flattened, in a circular pattern. Everything outside that circle was standing upright. That is, a funnel of unusual strength had grounded exactly there, all 2m of it. 60kt or more, in circular form, and confined to 2m diameter, in a storm of average 30kt or less.
Now, something like that isn't going to disturb an A320, because it is too localised (I once had a dust devil go right over me, and my parked airplane, at the Mammoth Lakes airport in the Sierras. Entertaining, not worrying). But widen it three or four times, as in a serious storm, and you have something that could kip a wing. Or flatten a golfer.
PBL
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XPMorten,
that's sort of about the level from which I guessed you were coming. Thanks for confirming.
I don't consider that what is written in AI training manuals predicts Nostradamus-like what would happen at EDDH at 1255Z on 01.03.08. I think it's a gust.
PBL
that's sort of about the level from which I guessed you were coming. Thanks for confirming.
I don't consider that what is written in AI training manuals predicts Nostradamus-like what would happen at EDDH at 1255Z on 01.03.08. I think it's a gust.
PBL
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Sorry. PBL, I have to support XPMorton here. The yaw-roll-decoupling cannot take ' a holiday', since there is no 'real' yaw-roll decoupling as far as I have understood Airbus FBW control law logic! But well, correct me if I'm wrong....
If a roll is commanded, Normal Law will adjust pitch to provide additional lift to keep level flying as well as rudder for a coordinated turn.
But vice versa, if you apply rudder, the A320 will (initially) exhibit a roll due to yaw-roll-coupling as any other swept wing aircraft. The control law does not automatically and simultaneously compensate this roll moment by opposite aileron deflection.
But yes, the FBW control logic will nevertheless react to this roll, but different as you might assume reffering to a true 'yaw-roll-decoupling'.
As far as I understand, the Normal Law provides 'roll stabilization' as long as there is no stick input, i.e. it will counteract any uncommanded roll and try to return to previous bank angle. Thus the Normal Law does 'see' the rolling of the A/C due to rudder deflection like an 'external' disturbance resulting in an uncommanded roll ('as long as the stick is untouched).
So there is a kind of 'yaw-roll decoupling' through the back door.
But this is a significant difference to a true 'feed-forward' yaw-roll deccoupling where the controller would know in advance about the A/C behaviour to a rudder deflection and thus would apply the appropriate aileron. But if the controller sees the roll as an external disturbance, the controller does not 'know' about the size of the disturbance and thus not the required control action. The reaction will be a result of actual/nominal value difference, applied control law, and gain factors and thus can be significantly slower up to the fact that depending on the implemented law a finite residual error might remain....
And thus as the manual cited by XPMorton points out or Chris practical experiences report, into the wind aileron has to be applied to keep wings level or the upwind wing down during fast decrab.
And I guess we don't need to discuss that rudder on swept wing A/C is a very strong roll control that can even outperform aileron capacity (remember 737). So no wondering that the wing coms up fast durind this 'significant' decrabbing'....
Regards, ihg
P.S.: I don't believe in the gust story....mean cross wind component was high enough to have the A/C drifting across the runway as seen ...
If a roll is commanded, Normal Law will adjust pitch to provide additional lift to keep level flying as well as rudder for a coordinated turn.
But vice versa, if you apply rudder, the A320 will (initially) exhibit a roll due to yaw-roll-coupling as any other swept wing aircraft. The control law does not automatically and simultaneously compensate this roll moment by opposite aileron deflection.
But yes, the FBW control logic will nevertheless react to this roll, but different as you might assume reffering to a true 'yaw-roll-decoupling'.
As far as I understand, the Normal Law provides 'roll stabilization' as long as there is no stick input, i.e. it will counteract any uncommanded roll and try to return to previous bank angle. Thus the Normal Law does 'see' the rolling of the A/C due to rudder deflection like an 'external' disturbance resulting in an uncommanded roll ('as long as the stick is untouched).
So there is a kind of 'yaw-roll decoupling' through the back door.
But this is a significant difference to a true 'feed-forward' yaw-roll deccoupling where the controller would know in advance about the A/C behaviour to a rudder deflection and thus would apply the appropriate aileron. But if the controller sees the roll as an external disturbance, the controller does not 'know' about the size of the disturbance and thus not the required control action. The reaction will be a result of actual/nominal value difference, applied control law, and gain factors and thus can be significantly slower up to the fact that depending on the implemented law a finite residual error might remain....
And thus as the manual cited by XPMorton points out or Chris practical experiences report, into the wind aileron has to be applied to keep wings level or the upwind wing down during fast decrab.
And I guess we don't need to discuss that rudder on swept wing A/C is a very strong roll control that can even outperform aileron capacity (remember 737). So no wondering that the wing coms up fast durind this 'significant' decrabbing'....
Regards, ihg
P.S.: I don't believe in the gust story....mean cross wind component was high enough to have the A/C drifting across the runway as seen ...
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Chris,
If I remember correctly, flying in DIRECT LAW during initial training was one the many exercises to be practiced. To do so I believe the instructor had to switch a few (?) flight control computers off and airplane was behaving like any conventional one with the necessary use of manual pitch trim.
The example you mention is part of some emergency situations where some flight controls surfaces are inhibited and therefore cannot be placed in a similar category.
As you mentioned, take-off is conducted in Roll Direct Law, once airborne a few conditions apply FCOM 1.27.20 P1 and within 5 seconds Roll and Pitch blend in the flight mode.
I don’t see how a reverse process couldn't occur sometime before the flare ?
Adequate flight test program would tell how and where the switch is more appropriate, my guess would be around 1000 ft …
Regarding sidestick philosophy:
Standard Operation Procedures require any Flight Crew Member to advise the other one whenever any control is manipulated … and strangely enough, the most important control is manipulated in complete darkness !?
I say it again loud and clear:
Invisible sidestick for a single crew operation: ANYTIME !
Invisible sidesticks for a crew operation: NON SENSE !
Dream Land,
Forecast were windy, and last wind check (if EDDHATC information is reliable) was even more, but in the chart considering runway condition.
So what do you do ?
Wait for the blue blue sky to hit again ?
I would feel comfortable to monitor even a low time PF as long as I can follow any of his control inputs … but I’m afraid FBW Airbus just does not provide that ultimate tool.
If I remember correctly, flying in DIRECT LAW during initial training was one the many exercises to be practiced. To do so I believe the instructor had to switch a few (?) flight control computers off and airplane was behaving like any conventional one with the necessary use of manual pitch trim.
Flight Crew Training Manual
Handling characteristics are natural, of high quality aircraft
Handling characteristics are natural, of high quality aircraft
As you mentioned, take-off is conducted in Roll Direct Law, once airborne a few conditions apply FCOM 1.27.20 P1 and within 5 seconds Roll and Pitch blend in the flight mode.
I don’t see how a reverse process couldn't occur sometime before the flare ?
Adequate flight test program would tell how and where the switch is more appropriate, my guess would be around 1000 ft …
Regarding sidestick philosophy:
Standard Operation Procedures require any Flight Crew Member to advise the other one whenever any control is manipulated … and strangely enough, the most important control is manipulated in complete darkness !?
I say it again loud and clear:
Invisible sidestick for a single crew operation: ANYTIME !
Invisible sidesticks for a crew operation: NON SENSE !
Dream Land,
Forecast were windy, and last wind check (if EDDHATC information is reliable) was even more, but in the chart considering runway condition.
So what do you do ?
Wait for the blue blue sky to hit again ?
I would feel comfortable to monitor even a low time PF as long as I can follow any of his control inputs … but I’m afraid FBW Airbus just does not provide that ultimate tool.
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#400 post says the manual states with a smooth rudder decrab little aileron correction is needed but with aggresive rudder decrab, which was the case here, opposite aileron is required to keep the wing from rising like all non AB aircraft. The bank seems to have followed the rudder input putting the upwind wing up causing the downwind drift. The FDR will tell the story if we ever see it here.
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Military Pilots
Hi Bubber44. Thanks for clarifying your comment re military pilots being prone to overcontrol on finals. No, I have never flown on a B52. My Boeing experience is limited to the B707 and the B747. Lockheed C130's (A-E-H) and L1011 were the others. Happy landings, Old Fella.
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ihg,
thanks for explaining carefully to those who didn't understand it how yaw-roll decoupling works on the A320.
But I do admit to being a bit puzzled by some of your post, as in:
where you contradict yourself. I am not sure what you mean by "real", or "true" here. You do say:
but I think you're trying to make a distinction without a corresponding technical correlate.
The ELAC gets signals from roll-rate sensors somehow and if the stick is neutral it signals the control-surface actuators to counter the roll. How else is decoupling supposed to work?
I wasn't talking about drift. I was talking about the wing lifting and what caused it. That is what let to the strike.
PBL
thanks for explaining carefully to those who didn't understand it how yaw-roll decoupling works on the A320.
But I do admit to being a bit puzzled by some of your post, as in:
Originally Posted by ihg
there is no 'real' yaw-roll decoupling as far as I have understood ...... So there is a kind of 'yaw-roll decoupling' .....
Originally Posted by igh
a true 'feed-forward' yaw-roll deccoupling where the controller would know in advance about the A/C behaviour to a rudder deflection and thus would apply the appropriate aileron
The ELAC gets signals from roll-rate sensors somehow and if the stick is neutral it signals the control-surface actuators to counter the roll. How else is decoupling supposed to work?
Originally Posted by ihg
I don't believe in the gust story....mean cross wind component was high enough to have the A/C drifting across the runway as seen ...
PBL
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I would feel comfortable to monitor even a low time PF as long as I can follow any of his control inputs
