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HAWK21M
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Cause - Aquaplaning Or Autobrake/Antiskid Problem

Wed Sep 21, 2005 4:47 pm

http://i2.photobucket.com/albums/y2/HAWK21M/4Rb.jpg

http://i2.photobucket.com/albums/y2/HAWK21M/1Ld.jpg

In case both Outboard Tires have such a skid mark.Operating in Rain after landing.Can the cause be attributed to Malfunctioning Autobrake/Antiskid or is it a case of Aquaplaning.
I feel the former.My seniors differ.
Anyone.
Also if it was aquaplaning why not all four main wheels.
regds
MEL
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FredT
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Wed Sep 21, 2005 6:25 pm

If an aircraft is aquaplaning, it is sliding on a sheet of water. It would have to be pretty darn rough water to wear down a tyre like that! Besides, the wheel would still rotate slightly unless the brakes were applied... and in the latter case, an operational anti-skid system should react and release brake pressure until the wheel starts spinning agian.

Perhaps aquaplaning combined with dried patches could do it... but the wheel would still have to remain locked somehow. Is there a lower limit to the pressure the anti-skid system can reduce the brake pressure to?

Of course, aquaplaning won’t mean having to foot a maintenance bill...  Yeah sure

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Fred
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MD11Engineer
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Wed Sep 21, 2005 7:15 pm

Just bite the A/S system. This doesn't take too long.
BTW, aquaplaning literally melts the rubber away, you'll have molten rubber all over the place.
The A/S system should sense the wheel locking and should release the brakes, which it obviously didn't do. From the pictures I would suspect a faulty A/S system. There are no drops of molten rubber visible.

Jan
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mandala499
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Wed Sep 21, 2005 7:25 pm

Unless the aircraft was aquaplaning on molten lava...
Antiskid failure...
or failure of the air/ground logic (resulting in spoilers not deploying and autobrake remaining in armed position and not activating... throttle not idle is a possibility too, then the pilot decided something's wrong and put max manual braking and result is skid... but my finger's at spoiler not deploying on time).

Or... HYD SYS A (if 737) failed resulting in manual braking on outboard wheels... but this requires a fail of the inboard accumulators.

HYD SYS B fail? The brakes remained after landing roll and therefore dragged the outboard wheels...

Quite possible in wet conditions and not getting noticed until someone sees the wheel...

Just my unqualified guesses *runs for cover*

Mandala499
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HAWK21M
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Wed Sep 21, 2005 10:19 pm

Quoting MD11Engineer (Reply 2):
Just bite the A/S system. This doesn't take too long

A/S tested ok.Pilot did use Autobrake though.Can it be Autobrake Outbd system B malfunction.Why does it not show on test.
What do you think of the Tire condition.
NO-GO right.
regds
MEL
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MD11Engineer
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Wed Sep 21, 2005 10:48 pm

The tyre has to be changed. It has been worn down trough the thread reenforcement plies.

Jan
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HAWK21M
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Wed Sep 21, 2005 10:53 pm

Quoting MD11Engineer (Reply 5):
The tyre has to be changed. It has been worn down trough the thread reenforcement plies.

Thats what happened.though a few disagreed.I wonder why  Smile
regds
MEL
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Pihero
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Wed Sep 21, 2005 11:48 pm

Hi, Guys.
Sorry to disagree with most of you.
Had it been a locked wheel, the wear would have been the deepest at the center of the tyre.
The tyres show a pattern of a lesser contact around the centre of the most worn area , then around it another ring of wear.Especially visible on the upper picture,the shape of the teardrop massed water (wider at the front, thinner at the back) is the proof of some degree of aquaplaning.
The absence of traces of globs of molten rubber is caused by the subsequent "normal" braking and taxi.

Just my two euro cents.
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FredT
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Wed Sep 21, 2005 11:50 pm

Quoting MD11Engineer (Reply 2):
BTW, aquaplaning literally melts the rubber away, you'll have molten rubber all over the place.

Only in rubber reversion hydroplaning though, right? In theory, there should be no real damage done from viscous/dynamic hydroplaning... albeit I suspect that in the real world, there'll be some potential for less-than-nominal things occuring, as hinted in my previous post.

For those going "what is he on about this time":

http://www.jet-jobs.com/articles/hydropln.html
http://ap.bridgestone.co.jp/pdf/Recommended_Action2.pdf

Cheers,
Fred
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Jetlagged
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Thu Sep 22, 2005 3:02 am

Without the system schematics in front of me I'm guessing, but if the antiskid is not showing a fault it could be one of the inputs to the outboard wheel antiskid system which was at fault, preventing it operating and causing the locked wheels.

Something in the logic, which tests fine on ground static, but disabled the outboard antiskid before or after touchdown.

The AMM should show all the logic which enables the system and should give a clue as to what might have caused the problem. Presumably the crew did not get a warning light, which might also help you identify the problem.
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HAWK21M
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Thu Sep 22, 2005 1:21 pm

Quoting Jetlagged (Reply 9):
but if the antiskid is not showing a fault it could be one of the inputs to the outboard wheel antiskid system which was at fault, preventing it operating and causing the locked wheels.

Thats what I thought too.

Quoting Jetlagged (Reply 9):
Presumably the crew did not get a warning light, which might also help you identify the problem.

No Warning light.In fact the Crew never knew of any Abnormal situation,Until Mx Informed them that Unscheduled Mx was called for & the wheels needed to be replaced.

Also if its Aquaplaning,why not on all four wheels.

regds
MEL

[Edited 2005-09-22 06:22:24]
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Jetlagged
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Fri Sep 23, 2005 1:21 am

Quoting HAWK21M (Reply 10):
Also if its Aquaplaning,why not on all four wheels.

The wheels would not have aquaplaned if the water depth on the runway was not too great. Do you know what the depth of water was? However a wet runway would reduce coefficient of friction, leading to locked wheels if antiskid did not operate properly.

Whether the wheels aquaplaned or not is incidental. The locked wheels did the damage. Aquaplaning would actually delay the tyre damage by preventing the tyres contacting the runway surface.
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FredT
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Fri Sep 23, 2005 6:04 am

Rubber reversion aquaplaning will happen even with runways which are little more than damp though, from what I have heard.

I must point out that this is not my area of expertise, if it is not apparent.  Smile
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HAWK21M
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Fri Sep 23, 2005 2:09 pm

Quoting Jetlagged (Reply 11):
The wheels would not have aquaplaned if the water depth on the runway was not too great. Do you know what the depth of water was

No idea on the level of water,but there was rain for last 12-13 hrs.
If Aquaplaning occurs wouldn't it occurs on all 4 wheels.Paired wheel occurances point out to Antiskid/Autobrake problems.
regds
MEL
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Pihero
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Fri Sep 23, 2005 5:33 pm

Quoting HAWK21M (Reply 13):
If Aquaplaning occurs wouldn't it occurs on all 4 wheels.Paired wheel occurances point out to Antiskid/Autobrake problems.

Not necessarily. One has to take account of the evenness of the runway surface for a sheet of water at least as wide as the airplanes base...
My opinion is that we see here the result of a wing down -and by not much- landing :the wheels on that side touched down first and aquaplaned. I bet it was very soft and the speed brakes took a longer time than usual to extend.

Am I right or am I wrong?
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HAWK21M
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Fri Sep 23, 2005 10:09 pm

Quoting Pihero (Reply 14):
the wheels on that side touched down first and aquaplaned.

In that case the Skid marks would be on #1&2 or #3&4.Why #1 & #4 ie Outboard Tyres.
regds
MEL
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Jetlagged
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Sat Sep 24, 2005 1:08 am

Quoting HAWK21M (Reply 13):
If Aquaplaning occurs wouldn't it occurs on all 4 wheels.Paired wheel occurances point out to Antiskid/Autobrake problems.

The problem seems most likely to be antiskid related. Aquaplaning might have been what caused the wheels to lock up in the first place, but not necessarily. One way or another, the runway was wet enough for the wheels to lock under braking.
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HAWK21M
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Sat Sep 24, 2005 2:16 pm

Quoting Jetlagged (Reply 16):
Aquaplaning might have been what caused the wheels to lock up in the first place, but not necessarily. One way or another, the runway was wet enough for the wheels to lock under braking.

Also #1 wheel had two skid marks seperated 90 deg apart,one Shallow & one prominent,where as #4 had one similiar prominent mark.
regds
MEL
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Jetlagged
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Mon Sep 26, 2005 12:30 am

Quoting HAWK21M (Reply 17):
Also #1 wheel had two skid marks seperated 90 deg apart,one Shallow & one prominent,where as #4 had one similiar prominent mark.

That implies the left wheel locked briefly, released, then locked again. Possibly there was a dry patch on the left side of the runway. Alternatively, if the problem was caused by wheel speed sensors, the fault on the left wheel was intermittent.
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HAWK21M
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Mon Sep 26, 2005 1:00 pm

Quoting Jetlagged (Reply 18):
Possibly there was a dry patch on the left side of the runway.

Would not Aquaplaning affect all Four Wheels.If only the Outboard wheels was affected & Auto brakes were used.Could A/B malfunction be a cause.
regds
MEL
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troubleshooter
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Mon Sep 26, 2005 3:57 pm

Quoting HAWK21M (Reply 19):
Could A/B malfunction be a cause.

I don´t think so. Even with autobrake in use the anti-skid system is in operation and should prevent wheel skid. I would go for a fault in the anti-skid system as the fault is "symmetrical" (wheels 1+4).
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abbs380
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Mon Sep 26, 2005 5:15 pm

Mel, Im shooting from the hip, to use an American term. Unless I missed it I dont think you even said what kind of a/c this is.
I definately agree this is an anti-skid problem, not what we call in the U.S. hydroplaning. Yes both tires (tyres) should have been changed.
Again, Im guessing, that both wheels are sending speed signals to the a/s system so the speed sensors are probably ok, but the brake release signal is not geting to the a/s control valves. Has any maint. been done on any of that recently? Many times on Airbus a/c I have found pushed back cannon plug pins which cause all sorts of problems. I would look for a problem at the control valves. Check the schematics manual for a common point.
 
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HAWK21M
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Tue Sep 27, 2005 1:10 am

Quoting Abbs380 (Reply 21):
I dont think you even said what kind of a/c this is.

This was a B732 Freighter.Its been concluded to be an Aquaplaning cause.But Im not convinced & still think its Autobrake error thru A/S valves,as The paired wheels were Involved.Although tests returned Normal.
regds
MEL
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Pihero
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Tue Sep 27, 2005 2:09 am

HAWK21M,

Sorry I misread your original post.
But I still stick to my guns as for the erosion marks on those wheels Embarrassmentn an antiskid induced locked wheel, you would have a "flat", which is not pertinently the case as "something" prevented some even contact of the wheel on the runway. That something was imo a ring of water .

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Electech6299
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Tue Sep 27, 2005 1:42 pm

Quoting FredT (Reply 12):
I must point out that this is not my area of expertise, if it is not apparent.

Ditto.  Wink

Quoting Abbs380 (Reply 21):
Again, Im guessing, that both wheels are sending speed signals to the a/s system so the speed sensors are probably ok, but the brake release signal is not geting to the a/s control valves.

I like this explanation. I don't know about the big planes, but I know a bit about logic...If there was no warning light and electronic diagnostics came back clean, that points to a mechanical fault-(perhaps in an electromechanical interface, like the a/s control valves?) that for one reason or another was not indicated on the wheel speed sensors. Again, I don't know, but I would think it works more or less like the antilock on autos, commercial trailer brakes and light craft, by pulsing the hydraulics with timed releases of pressure to allow the wheel to regain traction. So....assuming I understand correctly:

a) wheel brakes and speed sensors on all four wheels
b) inboard & outboard on isolated hydraulic circuits.
c) antiskid valves on all four hydraulic circuits
d) antiskid logic paired to inboard and outboard (2 distinct logic functions)

I would expect the logic function to be something like this:
1. The antiskid logic reference is established with wheel speed sensor readings after WOW is indicated.
2. If readings indicate differential variation (unilateral skid), the affected wheel is released.
3. If the wheel speed drops faster than a pre-programmed parameter (bilateral skid), both wheels are released.
4. When the wheel speed increases to a pre-programmed parameter (what the computer considers the same as the other wheel, or 3 wheels), the anti-skid ceases and full hydraulic pressure from the manual or Autobrake is restored.

Quoting HAWK21M (Reply 13):
there was rain for last 12-13 hrs

This would indicate a planar water surface with defined flow patterns and no residual oils...not the worst braking environment, but depending on water depth there could be hydroplaning.

Quoting HAWK21M (Reply 10):
No Warning light.In fact the Crew never knew of any Abnormal situation,

I would hope that the CMOS chip retains fault histories, like cars do...In which case the a/s never registered a fault. I would wonder...using the same assumptions (A thru D above), Do the inboard and outboard logic circuits compare readings? Would a difference in inboard and outboard wheel speeds register a fault? Perhaps the outboard a/s logic never received the WOW signal- or the outboard wheels didn't ever spin enough to create an initial speed reference.

Are there mechanical differences in the inboard and outboard brakes? (i.e. is one stronger? Could one be applied without the other?)

And finally, if there was this dichotomous function- the inboard antiskid functioning but the outboard not- could this be caused by hydroplaning briefly in the crucial time following touchdown when the logic chips register weight on wheels?

Perhaps hydroplaning is the culprit, causing an a/s failure by inhibiting WOW reference. Quite complex and purely hypothetical, I like the a/s valve failure better, it's simpler and it can be fixed...  Smile
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HAWK21M
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RE: Cause - Aquaplaning Or Autobrake/Antiskid Problem

Tue Sep 27, 2005 5:29 pm

Quoting Electech6299 (Reply 24):
And finally, if there was this dichotomous function- the inboard antiskid functioning but the outboard not- could this be caused by hydroplaning briefly in the crucial time following touchdown when the logic chips register weight on wheels

Thats what seems to be the Most logical Explanation.The confusion is because only the Outboard wheels had the Marks.
regds
MEL
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