Dalmd88
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A320 Nose Gear Incidents

Thu Sep 22, 2005 6:51 pm

So how many times has the nose gear done the 90 degree swing on the A320? MSNBC brought up a America West in 99. I have heard of UA and JB having the same thing happen in 02. That seems like a lot of similar incidents.
 
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HAWK21M
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RE: A320 Nose Gear Incidents

Thu Sep 22, 2005 6:58 pm

What was the cause of this 90 deg deflection.Arnt the Centering cams present in the Strut.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
Dalmd88
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RE: A320 Nose Gear Incidents

Thu Sep 22, 2005 7:06 pm

I'm not real familar with the A320, but I always though all nose gears had a centering cam that would aline the tires straight. The 'expert' on TV read of the Am West NTSB report and it sounded like an o-ring failed allowing the steering actuator to command full deflection while in flight.
 
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HAWK21M
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RE: A320 Nose Gear Incidents

Thu Sep 22, 2005 9:52 pm

Quoting DALMD88 (Reply 2):
The 'expert' on TV read of the Am West NTSB report and it sounded like an o-ring failed allowing the steering actuator to command full deflection while in flight

Wouldn't the Steering be having an Air-Grd sense to it.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
glidepath73
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RE: A320 Nose Gear Incidents

Thu Sep 22, 2005 10:23 pm

A friend of mine (works for Airbus) says, the reason for the blocking steering system on the nose wheel was maybe caused by a overpressure in the nitrogen bubble inside the nose wheel damper system.
If you fill to much nitrogen in there, a possible blocking of the steering system is very likely.

Can anybody confirm this?

Seems the incident was possible caused again by a maintenance mistake.

Regards,
Patrick
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PPVRA
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RE: A320 Nose Gear Incidents

Thu Sep 22, 2005 11:10 pm

So, how hot did that landing gear get?  hot 

What should we expect to see what's left of it?

Pictures anyone?

Cheers
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DL_Mech
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RE: A320 Nose Gear Incidents

Fri Sep 23, 2005 12:57 am

Doesn't the computer for nosewheel steering automatically turn the nosegear 90 degrees during a failure?
This plane is built to withstand anything... except a bad pilot.
 
Bobster2
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RE: A320 Nose Gear Incidents

Fri Sep 23, 2005 1:37 am

Quoting PPVRA (Reply 5):
So, how hot did that landing gear get?

I didn't see fire fighters put a single drop of water on it. If it had been dangerously hot I'm sure they would have sprayed it. Perhaps the heat was carried away from the landing gear as the magnesium rims burned as blew away. The pilots made the landing as long and cool as they could. I assume the airplane was designed for this type of landing, if not they would have to make the nosegear system fail safe and they obviously haven't done that.
"I tell you this, no eternal reward will forgive us now for wasting the dawn." Jim Morrison
 
EMBQA
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RE: A320 Nose Gear Incidents

Fri Sep 23, 2005 11:21 am

Quoting Dl_mech (Reply 6):
Doesn't the computer for nosewheel steering automatically turn the nosegear 90 degrees during a failure?

Gotta love that Airbus design...!!! Yup, that is true. I was talking with one of the Mech's in our hangar today that has several years of A320 time, and that is what he told me it will do if the computer fails. You'd THINK they would desing it to default to 0

Quoting HAWK21M (Reply 1):
Arnt the Centering cams present in the Strut.

Nope, unlike most nose struts you'd think of.. the Airbus relies on the computer to do that and it has NO centering cam...!!
"It's not the size of the dog in the fight, but the size of the fight in the dog"
 
320tech
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RE: A320 Nose Gear Incidents

Fri Sep 23, 2005 11:35 am

Doesn't the computer for nosewheel steering automatically turn the nosegear 90 degrees during a failure?

Okay, that I have to look up. I think I would have remembered that.

reason for the blocking steering system on the nose wheel was maybe caused by a overpressure in the nitrogen bubble inside the nose wheel damper system.

There's no nosewheel damper. I suspect you're referring to the nose oleo. There is no connection between the gas pressure inside the strut, and the hydraulic pressure in the steering system.

The A320 has a known fault with o-rings in the NLG steering, which may cause uncommanded turning of the nosewheel. Here's a link to the NTSB report on the America West incident:


http://www.ntsb.gov/ntsb/brief2.asp?...205X00227&ntsbno=NYC99IA062&akey=1

This was posted in another thread, thanks to whoever the original poster was - can't remember which thread it was.
The primary function of the design engineer is to make things difficult for the manufacturer and impossible for the AME.
 
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HAWK21M
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RE: A320 Nose Gear Incidents

Fri Sep 23, 2005 1:54 pm

Quoting Bobster2 (Reply 7):
Perhaps the heat was carried away from the landing gear as the magnesium rims burned as blew away.

Any secondary damage caused by FOD.

Quoting EMBQA (Reply 8):
I was talking with one of the Mech's in our hangar today that has several years of A320 time, and that is what he told me it will do if the computer fails. You'd THINK they would desing it to default to 0

Exactly why 90 deg.

Quoting EMBQA (Reply 8):
Nope, unlike most nose struts you'd think of.. the Airbus relies on the computer to do that and it has NO centering cam...!!

The Centering cams would have helped in such cases.

Whats the priliminary report say.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
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DL_Mech
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RE: A320 Nose Gear Incidents

Fri Sep 23, 2005 9:32 pm

Quoting HAWK21M (Reply 10):
Exactly why 90 deg.

As it was explained to me, since the A320 is "Steer By Wire," a plane with the nosegear at 90 deg. has a much better chance of staying on the runway ( such as the B6 incident) than a gear that is unsteerable, and not locked at 0 degrees.

I'm no 320 expert, and this info could be wrong.......
This plane is built to withstand anything... except a bad pilot.
 
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HAWK21M
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RE: A320 Nose Gear Incidents

Fri Sep 23, 2005 10:07 pm

Quoting Dl_mech (Reply 11):
a plane with the nosegear at 90 deg. has a much better chance of staying on the runway ( such as the B6 incident) than a gear that is unsteerable, and not locked at 0 degrees.

So why not "Lock" at 0 deg.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
AvionicMech
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RE: A320 Nose Gear Incidents

Fri Sep 23, 2005 11:21 pm

Quoting HAWK21M (Reply 12):
So why not "Lock" at 0 deg.
regds
MEL

I think the reason would be because the aircraft does not know exactly where 0 degrees is. I have not worked on an A320 but it would seem that as it is 'steer by wire' the movement is only commanded by the computers and needs a feedback to know when the wheels are straight and therefore to stop porting hydraulic pressure to one of the steering actuators and stop the movement. But in the case of the dual failure as mentioned above, all the system does is port the hydraulic pressure to one of the actuators and turn it all the way to the stops. Some people might think well why not just put equal hydraulic pressure to either side of the steering and that will straighten it up but it won't, that will only keep it in the position that it is in when it fails which could be anywhere in its range of movement.

Hope that makes sense

Avionic Mech
 
amtrosie
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RE: A320 Nose Gear Incidents

Sat Sep 24, 2005 12:09 pm

ALL RIGHT, I went to my books!! (on a Friday night at that) thus proving I have no life!!

Quoting EMBQA (Reply 8):
Nope, unlike most nose struts you'd think of.. the Airbus relies on the computer to do that and it has NO centering cam...!!

My books indicate that there ARE indeed centering cams in the oleo strut. It does not, however, mention anything about the possibility of a steering computer failure and its failure mode. Sooooo... I am anxious to hear from

Quoting 320tech (Reply 9):
Okay, that I have to look up. I think I would have remembered that.

My books are for line guys and not that comprehensive.
 
320tech
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RE: A320 Nose Gear Incidents

Sat Sep 24, 2005 1:10 pm

Well, my books aren't anything great, but I will give a bit of a synopsis.

- two handwheels (pilot and co-pilot) - in case of simultaneous operation, the movements are added - max travel with the handwheel is 75 degrees - they shut off at >130 kts

- rudder pedals - max travel 6 degrees

- NWS selector valve shuts off pressure to NWS when the strut is extended, when towing, and when airspeed > 80 kts

- when the strut is fully extended on take-off, a centring cam centres the wheels

- steering control is electrohydraulic with position feedback of the NW (in other words, the airplane does too know where the nosewheels are pointed). If the BSCU failed, then the airplane wouldn't know, and steering would be de-activated

- the Brake and Steering Control Unit (BSCU) monitors the system and de-activates it in case of a failure which may cause wheel runaway. Unfortunately, just when the book gets interesting, it moves on to other things.

- because the NWS hyd pressure is tapped off the NLG door closing pressure line, NWS is lost in a free fall extension (because the NLG doors don't close)

- as soon as the gear is extended for landing, a test of the steering control is made. The selector valve is energised, and 10 seconds after NLG is downlocked, a small steering signal is sent to the NWS, which turns less than 2 degrees. The test stops when the mains touch down

So this is more than most people want to know, I bet, and I still haven't answered the question. I will try to look up the service bulletin (A320-32-1197) and the AMM on Monday to see if I can figure it out.

-
The primary function of the design engineer is to make things difficult for the manufacturer and impossible for the AME.
 
jetfixer
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RE: A320 Nose Gear Incidents

Sun Sep 25, 2005 12:18 pm

Quoting Dl_mech (Reply 6):
Doesn't the computer for nosewheel steering automatically turn the nosegear 90 degrees during a failure?

I too have not heard of this.
As mentioned by others the NLG does have a centering mechanism.
It has been more than 7 years since I repacked a A319/320 nose strut, but here is what I remember.
The centering cam must be clocked correctly when reassembling the upper and lower struts.
When installing the strut assy into the outer cylinder it must also be clocked, this part is very easy to get wrong cause the keyway is at the top of the outer cylinder and is hard to see. It is either keyed or not. If its not keyed properly the inner cylinder will rotate when W off W and strut extended.
After assy we'd push the strut into the outer cylinder and turn the strut to approx 45 deg LT and RT and pressurize the strut with Nitrogen. The strut would extend and center and should be locked center. I have seen the strut turn 45 and 90 deg during this test because of improper assy.
That would be my guess as to what may have happened.
It's not one of the easier struts I've repacked.

Later
 
avioniker
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RE: A320 Nose Gear Incidents

Mon Sep 26, 2005 9:51 pm

Food for thought

Failure of the position feedback signal will cause the nose gear to go to the extreme of travel looking for center. That coupled with O ring failure in the Bugatti valve on rotation will cause the gear to remain in that position. (I got to help replace all those valves in 99 and 00 at HP.)

The centering cam won't overcome a hardover steering signal if the gear is already there by the time the strut is fully extended.
It doesn't really matter what the book says, there are 9 documented landings in that condition and who knows how many more that didn't result in news coverage.

The gear being at 90 degrees after a failure is not a failure design. It's coincidence. At landing (or takeoff) speed the nose wheel steering is 100% ineffective at steering the aircraft and once the tires blow it's inertia, rudder, and differential braking, not steering, that keeps it on the centerline.

Congrats to the crews that have had to deal with it.

 Smile
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Starlionblue
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RE: A320 Nose Gear Incidents

Mon Sep 26, 2005 10:31 pm

Quoting Avioniker (Reply 17):

Failure of the position feedback signal will cause the nose gear to go to the extreme of travel looking for center. That coupled with O ring failure in the Bugatti valve on rotation will cause the gear to remain in that position. (I got to help replace all those valves in 99 and 00 at HP.)

So what your're saying is that if the 0 ring is fine the nose gear will eventually find center due to the centering cam?
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
avioniker
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RE: A320 Nose Gear Incidents

Tue Sep 27, 2005 2:29 am

That's one possibility. Too many engineers today aren't familiar enough with "Murphy's Law". Keep in mind that my post is merely based on my opinion resulting from personal experience.

Personally I think what you say has happened on a few occasions. If the centering cam system weren't effective I'm certain there would have been many more LAX style landings to go with the many steering fault write-ups I've worked.

There's way too many opportunities for failure in that particular NWS system for my comfort level. It's a testament to everyone from the engineers to the assemblers that there haven't been more.

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One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533
 
Dougloid
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RE: A320 Nose Gear Incidents

Tue Sep 27, 2005 11:06 pm

Quoting Dl_mech (Reply 11):
As it was explained to me, since the A320 is "Steer By Wire," a plane with the nosegear at 90 deg. has a much better chance of staying on the runway ( such as the B6 incident) than a gear that is unsteerable, and not locked at 0 degrees.

I'm no 320 expert, and this info could be wrong.......

that sort of sounds like making lemons out of lemonade to me...it's better to have a strut that does not have the possibility of taking itself to a 90 degree position despite all control inputs and other entreaties to the contrary.

One event would be more or less too much for me to tolerate.
If you believe in coincidence, you haven't looked close enough-Joe Leaphorn
 
320tech
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RE: A320 Nose Gear Incidents

Wed Sep 28, 2005 8:22 am

One event would be more or less too much for me to tolerate.

Then I guess you will never fly, drive, or use a computer, amongst many other uses of technology. According to your profile, you're both a lawyer and an A&P. I can see the lawyer in that statement, but not the A&P. As you must know, almost every item that goes onto an airplane is more complex than it appears at first glance. It's difficult, and sometimes impossible, to predetermine every failure. In jetBlue's case, there is a known defect for which a fix has been described. The question to be resolved, I think, is whether this is another occurrence of the same fault, or something else.

One of the reasons everything in aviation is so expensive is that we have designed and tested damn close to all the failures out of the parts.

Doesn't the computer for nosewheel steering automatically turn the nosegear 90 degrees during a failure?

Having looked through the book, there is no indication that steering to 90 degrees in a failure is a design feature. More likely, it's just the end of the steering gear.

Failure of the position feedback signal will cause the nose gear to go to the extreme of travel looking for center

From what I've seen, as soon as the BSCU detects a position failure, it should shut the steering off. The question is, how long does it take to do it? If it takes more than a second or two to shut off pressure, that's probably enough time to drive the gear over.

So what your're saying is that if the 0 ring is fine the nose gear will eventually find center due to the centering cam?

Shouldn't be eventual, should be right now. Ten seconds after the nose gear extends, the NWS begins a self-test. If a steering failure is detected, the BSCU will kick off, and you'll get a failure message on ECAM. Of course, the nose strut is fully extended throughout this time, so the centring cam is already doing its job.
The primary function of the design engineer is to make things difficult for the manufacturer and impossible for the AME.
 
airmech
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RE: A320 Nose Gear Incidents

Wed Sep 28, 2005 8:39 am

Dougloid quote: One event would be more or less too much for me to tolerate.

Dougloid: Well you certainly have a "cash cow" going on here. Please take up the cause make sure we are all safe from our selves. This is certainly a travesty and must be stopped. Plenty of resourses on this site for a case....
 
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lightsaber
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RE: A320 Nose Gear Incidents

Wed Sep 28, 2005 9:44 am

Quoting EMBQA (Reply 8):
You'd THINK they would desing it to default to 0

My boss, an ex-pilot, says this is to keep pilots for taxing the plane on the assumption the gear failed on the ground. If the gear fails 5 degrees off center, the "theory" is that the pilots wouldn't notice until they're skidding off the runway.

Quoting HAWK21M (Reply 10):

Exactly why 90 deg.

It stops the plane from taxing. Also, in an emergency landing, it keeps the plane from strearing in a preferential direction.

320 tech, nice post!

Lightsaber
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cactusTECH
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RE: A320 Nose Gear Incidents

Wed Sep 28, 2005 10:20 pm

When it happen to AWA, they found a bad O-ring in the steering module. Techs had changed the nose wheel steering module and did not position one of the orings correclty in the pressure line. When this o-ring gave up all the pressure shifted to one side since there was not enough pressure in the opposite actuator to put the wheel back in place.
 
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HAWK21M
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RE: A320 Nose Gear Incidents

Wed Sep 28, 2005 10:33 pm

Quoting CactusTECH (Reply 24):
When it happen to AWA, they found a bad O-ring in the steering module.

Why Isn't the Steering System Air-Grd sensed.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
320tech
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RE: A320 Nose Gear Incidents

Wed Sep 28, 2005 11:29 pm

Why Isn't the Steering System Air-Grd sensed.

The system uses the 2 LGCIU's (Landing Gear Control and Interface Unit) to detect weight on or off wheels. As mentioned, the system performs a test 10 seconds after gear extension (so it "knows" it's in the air, and it "knows" it's landing). It tests by moving the gear back and forth a little bit. If the o-ring has failed, when the system performs its test, the hyd pressure will push past the o-ring and drive the nose wheel fully one way.

If most or all of these incidents have resulted in the NW turning left, I would make the assumption that the test operates to the left first (which I believe it does). If it's not always left, then either the test doesn't always start to the left or else the o-ring is failing during the test.

I assume the NW must drive over quickly, because it seems to happen too fast for the BSCU to turn it off.

Barring someone coming up with an actual reference, I am convinced that the gear is not designed to turn ninety degrees, it just does in this failure mode. Also, I suspect it's not actually ninety, but probably ninety-five (the towing limit - probably a mechanical stop in there).

A "normal" failure (ie, the position of the NWS disagrees with the position the BSCU thinks it should be) would result in the BSCU turning off the NWS with the wheels within two degrees of centre, presumably close enough to maintain the centreline with brakes.
The primary function of the design engineer is to make things difficult for the manufacturer and impossible for the AME.
 
OPNLguy
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RE: A320 Nose Gear Incidents

Thu Sep 29, 2005 2:07 pm

Quoting DALMD88 (Thread starter):
I have heard of UA and JB having the same thing happen in 02

Here you go...

http://www.ntsb.gov/ntsb/brief.asp?ev_id=20021125X05520&key=1
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
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HAWK21M
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RE: A320 Nose Gear Incidents

Thu Sep 29, 2005 2:55 pm

Were there any Mods suggested to Avoid this from Reoccuring.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
aeroguy
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RE: A320 Nose Gear Incidents

Fri Sep 30, 2005 11:53 am

OK so just to recap here a bit for the benefit of my understanding since there have been quite a few posts in several different threads...

It would appear that the A320 does have a nose wheel centering cam and the incidents in which the gear was turned 90 degrees were not an intentional computer commanded "design feature"?

Also, there has been mention of a number of previous incidents but I have only been able to piece together 4 from what has been posted:

A320 AW N628AW
16-FEB-99 CMH
NTSB Report
FAA Report
Resulting in:
AD 99-23-09

A320 B6 N503JB
01-NOV-02 JFK
FAA Report

A319 UA N804UA
21-NOV-02 ORD
NTSB Report
FAA Report

A320 B6 N536JB
21-SEP-05 LAX
NTSB Report

Thanks to 320tech and others for their helpful information.
 
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HAWK21M
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RE: A320 Nose Gear Incidents

Fri Sep 30, 2005 2:52 pm

Quoting Aeroguy (Reply 29):

Excellent compilation.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
mrocktor
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RE: A320 Nose Gear Incidents

Sat Oct 01, 2005 5:26 am

Quoting Avioniker (Reply 19):
Too many engineers today aren't familiar enough with "Murphy's Law".

Good, else we'd never improve safety since every plane always crashes eh?

Quoting Dougloid (Reply 20):
it's better to have a strut that does not have the possibility of taking itself to a 90 degree position despite all control inputs and other entreaties to the contrary

No, actually it's not. 90 degrees is a lot less harmful than, say, 40 degrees. I'm guessing that the 90 degree position is not a "default" for the system, but is a cleverly devised hard stop for steering travel. This means that in the event of steering hardover the nosewheel is put in a position that does not cause continuous yaw imbalance on the ground.

If that's the case, its actually a very clever bit of engineering.

mrocktor
 
avioniker
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RE: A320 Nose Gear Incidents

Mon Oct 03, 2005 9:45 pm

Quoting Mrocktor (Reply 31):
Good, else we'd never improve safety since every plane always crashes eh?

Thank you for validating my assertion. But I'm not sure I understand you point.

In simplified form "If something can go wrong it will; corollary 1: At the most inopportune time."

Here's a link to some pics you may not have seen

http://www.avweb.com/news/features/190709-1.html

 Smile
One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533

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