Brake Problems led to A320 Skids
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Brake Problems led to A320 Skids
Very funny, gerryfoley, but you're not supposed to be marketing merchandise on PPPRuNe.
Assuming your post is not a spoof (a recent A320 runway overrun comes to mind), I will repeat myself by expressing the wish that Airbus and other manufacturers would make their connectors more Murphy-proof.
Assuming your post is not a spoof (a recent A320 runway overrun comes to mind), I will repeat myself by expressing the wish that Airbus and other manufacturers would make their connectors more Murphy-proof.
UkEng
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Connectors only need to be murphy proof when they are close together.
I can only see this has happened during manufacture of the landing gear or during harness replacement. If this is the case someone didn't do the function checks properly because the Airbus checks would cause this to be spotted very easily,
I can only see this has happened during manufacture of the landing gear or during harness replacement. If this is the case someone didn't do the function checks properly because the Airbus checks would cause this to be spotted very easily,
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ukeng,
The NTSB says:
"...inboard and outboard wheel speed tachometer wires were cross-connected..."
Does that tell you enough for a reasonable guess for the cross-over point? Assuming we do not need to look beyond the L/G.
The NTSB says:
"...inboard and outboard wheel speed tachometer wires were cross-connected..."
Does that tell you enough for a reasonable guess for the cross-over point? Assuming we do not need to look beyond the L/G.
UkEng
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ukeng,
The NTSB says:
"...inboard and outboard wheel speed tachometer wires were cross-connected..."
Does that tell you enough for a reasonable guess for the cross-over point? Assuming we do not need to look beyond the L/G.
The NTSB says:
"...inboard and outboard wheel speed tachometer wires were cross-connected..."
Does that tell you enough for a reasonable guess for the cross-over point? Assuming we do not need to look beyond the L/G.
Isn't the first time this sort of thing has happened. We had some burst tyres on our 767 fleet due to a similar foul up during mx.
Airbus state that replacement of 1 wheel speed transducer doesn't require a test as the BSCU will test it during taxi. However replacing more than one requires a spin up check due to the possibility of cross connection.
Interesting regardless
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Originally Posted by NTSB
...
Examination of maintenance records indicated that both main landing gear units were replaced on the incident airplane in early February 2008.
Examination of maintenance records indicated that both main landing gear units were replaced on the incident airplane in early February 2008.
Originally Posted by AMM
TASK 32-42-00-720-002-A
Functional test of the tachometers
1. Reason for the Job
The test below is to do the check of the tachometer for correct operation after a replacement of one of them.
NOTE : If the MLG WHEEL TACHYMETER DRIVING TOOL is not available, as an alternative you can use:
- two standard drilling machines with the DRIVING ADAPTOR (98D32403004000).
NOTE : You must do this test if there is a risk of wiring cross connection between two tachometers (replacement of the MLG or of the electrical
harness of the MLG).
If only one tachometer is replaced or disconnected, THIS TEST IS NOT MANDATORY as the BSCU will do the automatic check of the tachometer.The BSCU will do this check during aircraft roll between 10 m/s and 40 m/s (32.81 ft/s and 131.23 ft/s) to make sure that the tachometer operates correctly.
...
Functional test of the tachometers
1. Reason for the Job
The test below is to do the check of the tachometer for correct operation after a replacement of one of them.
NOTE : If the MLG WHEEL TACHYMETER DRIVING TOOL is not available, as an alternative you can use:
- two standard drilling machines with the DRIVING ADAPTOR (98D32403004000).
NOTE : You must do this test if there is a risk of wiring cross connection between two tachometers (replacement of the MLG or of the electrical
harness of the MLG).
If only one tachometer is replaced or disconnected, THIS TEST IS NOT MANDATORY as the BSCU will do the automatic check of the tachometer.The BSCU will do this check during aircraft roll between 10 m/s and 40 m/s (32.81 ft/s and 131.23 ft/s) to make sure that the tachometer operates correctly.
...
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The DC10 had a similiar problem with the anti skid brakes causing numerous tire failures/bursts.
certainly different in that it was brake lines and not wiring, but the concept should be well known.
And yes, the connectors SHOULD be murphy proof. Square, round, triangle, octagonal shapes etc.
interesting that some of the mx was done outside the usa.
Also, perhaps one should add this to a mental check list:
Things going to hell on landing? Anti skid switch off.
certainly different in that it was brake lines and not wiring, but the concept should be well known.
And yes, the connectors SHOULD be murphy proof. Square, round, triangle, octagonal shapes etc.
interesting that some of the mx was done outside the usa.
Also, perhaps one should add this to a mental check list:
Things going to hell on landing? Anti skid switch off.
UkEng
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And yes, the connectors SHOULD be murphy proof. Square, round, triangle, octagonal shapes etc.
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Originally Posted by ukeng
Nope, usually all round connectors just with different keyways. Not really viable to do that on the wheels as you'd need 4 different part number transducers just for a 319. Better to have people follow the AMM to the letter instead!
Inadvertent swap between left and right hand transducer connections, then?
Maybe 4 different part numbers WOULD have been cheaper in the long run....
Failing that, I would have gone for a wiring loom where it would have been physically impossible to connect the left wheel transducer to the right wheel loom. Not rocket science, I would have thought: make the loom lengths different, or sufficiently asymmetric. Been there, done that.
But I admit I don't have an A319 AMM or IPC at hand to have a close look.
Failing all that, a lick of coloured paint or a tag could have helped.... ?
CJ
UkEng
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Yep, don't know what the answer is really. Legs tend get dirty quickly and any labelling either gets covered in dirt or worn away over time.
Even if you had 4 different part numbers someone would still end up fitting No1 transducer to No2 wheel if the wiring was crossed.
Should never happen so long as the MM reference is clear (I believe it is in this case) and that same MM is followed.
Perhaps a software change in the BSCU could be made that would detect the wrong brake is being released? Not sure if that would be possible.
p.s. Different loom lengths wouldn't work either as the harness runs down the centre of the leg before splitting off down each axle , each axle being the same length.
Even if you had 4 different part numbers someone would still end up fitting No1 transducer to No2 wheel if the wiring was crossed.
Should never happen so long as the MM reference is clear (I believe it is in this case) and that same MM is followed.
Perhaps a software change in the BSCU could be made that would detect the wrong brake is being released? Not sure if that would be possible.
p.s. Different loom lengths wouldn't work either as the harness runs down the centre of the leg before splitting off down each axle , each axle being the same length.
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Originally Posted by ukeng
p.s. Different loom lengths wouldn't work either as the harness runs down the centre of the leg before splitting off down each axle , each axle being the same length.
As I said, I have no A320 AMM or IPC, so just quoting what I might have done to keep Murphy off my back.
Thanks for your answers!
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Basic stuff really, any danger of a cross connection, functionally split the system, and test to check for correct connection.....like has been quoted.
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Originally Posted by glad rag
..test to check for correct connection..
But Murphy is all about making sure the wrong connection cannot be made in the first place.
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IMHO of course....
1. The anti skid units/BSCU's or whatever name should test for cross coupled connectors by watching for appropriate wheel rotation when a sharp turn is negotiated with a 'do not takeoff' type prompt if it fails.
2. In the event that section 1 fails, have a back up mode to prevent tyre burst. (Thinks Hard braking one side with wheel rotation and no brake application on the other side with no wheel rotation...Something wrong. Lets do an e-swap of the sensors and see if it cures matters - May flat spot the tyre, but hopefully won't lead to loss of control). (I can imagine doing this for 320 style, but imagine writing the code for a 747! Nightmare!)
Ho hum, evening folks...
1. The anti skid units/BSCU's or whatever name should test for cross coupled connectors by watching for appropriate wheel rotation when a sharp turn is negotiated with a 'do not takeoff' type prompt if it fails.
2. In the event that section 1 fails, have a back up mode to prevent tyre burst. (Thinks Hard braking one side with wheel rotation and no brake application on the other side with no wheel rotation...Something wrong. Lets do an e-swap of the sensors and see if it cures matters - May flat spot the tyre, but hopefully won't lead to loss of control). (I can imagine doing this for 320 style, but imagine writing the code for a 747! Nightmare!)
Ho hum, evening folks...
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I had this exact scenario play out for me on a Gulfstream GII about 4 years back;
Landed at Burbank, Ca on a dry runway applied what felt like moderate braking below 90 kts only to feel the A/C lurch to the left and noticed the Anti-Skid fail light come on as we came to a stop. Taxied in to the ramp without noticing anything else unusual until we noticed maintenance running out to our left wing as we shut down. Turned out the inboard Left main tire looked like someone had taken a machette to it and had neatly chopped off about 1/5th of the tire exposing a gaping 10 x 6 inch hole! The outboard tire on the same wheelset was unaffected. The cause turned out to be cross connected hydraulic lines to the wheels during maintenance which had occured about 2 months prior.
Landed at Burbank, Ca on a dry runway applied what felt like moderate braking below 90 kts only to feel the A/C lurch to the left and noticed the Anti-Skid fail light come on as we came to a stop. Taxied in to the ramp without noticing anything else unusual until we noticed maintenance running out to our left wing as we shut down. Turned out the inboard Left main tire looked like someone had taken a machette to it and had neatly chopped off about 1/5th of the tire exposing a gaping 10 x 6 inch hole! The outboard tire on the same wheelset was unaffected. The cause turned out to be cross connected hydraulic lines to the wheels during maintenance which had occured about 2 months prior.
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FHA, following your advice, many pprune discussion couldn't be had, lacking the ready reference to the relevant source.
So far, limited quoting of copyrighted material has never been a problem for anyone, so please leave to the moderators the job of deciding what can be posted and what not.
So far, limited quoting of copyrighted material has never been a problem for anyone, so please leave to the moderators the job of deciding what can be posted and what not.
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It's possible to Murphy-proof almosr anything successfully, but the long-term result is a new generation of new & improved Murphies who find more and more creative ways to foul things up.
(Thinks: how many times have counter-rotating props been installed on the wrong engines? P-38, F-82, PA-39...)
(Thinks: how many times have counter-rotating props been installed on the wrong engines? P-38, F-82, PA-39...)