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A320 Nose Gear Question

rvsm410

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Ok just trying to understand why the A320 nose gear normally rotates before it is stowed in the up position? This seems like a very complex mechanical thing to do in light of all the other airliners built....
 

Makesheepnervus

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I was under the impression that the nose gear does not normally rotate when it retracts. The 90' rotation in the JB case was due to a yet undetermined malfunction (with the infamous bad O rings in the BGCU being the likely culprit).

Perhaps an A320 Pilot or Mechanic can set the record straight on this one.
 

erj-145mech

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My mixmaster nose gear turns 90 when it retracts also, not complicated at all. Some other planes that I've worked on that the gear rotates are P-40 main gear, F4U main gear, Rockwell Commander 500, 690, 695, 1000's main gear, MU-2 main gears, Beech 24 nose gear. None of it is really complicated, but not maintenance free either. Douglas SBD main gear has a cable that shrinks the main gear oleo struts to fit in the wheel wells.
 

CFI4LIFE

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I am by no means an expert on the subject, and this is second hand knowledge.. but from what I heard, the nose gear has a computer that automatically centers the nose wheel after rotation prior to going into the gear well. If the computer, or centering mechanism fails, then it blows to the 90 degree poisition, as we saw on JetBlue, so that upon landing the plane is less likely to veer to one side when the nose wheel touches down. Say for example the wheel froze at a 10 degree angle to the right, when the plane touches down guess where its going to head!


Like I said, this is just what I was told, take it with a grain of salt. Maybe more of an "Airbus" guru can confirm/clarify this.
 

User546

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Although I'm by no means an expert on Airbus operations, a good friend of mine is an A320 captain, and we were discussing this incident yesterday.

He said that when a certain part of the inner gear fails (some type of caster?), it's designed to blow to the 90 degree angle. He assumed that it was designed that way so that it would give the best chance of a good outcome in the same situation that we saw Wednesday. If when it blew, it went to the 45 degree angle, or freely any direction, it would almost insure a loss of directional control on landing. At the 90 degree point, the aircraft is less likely to go out of control, since its facing directly against the runway.

Maybe another Airbus jokey can make more sense of it then I!
 

User546

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Dang CFI4Life, I think we're on the same wave length today...
 

rvsm410

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Thanks for the explaination that makes sence...however why was it designed to rotate to start with? Is it a space issue in the lower forward structure? ...
 

A350

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The nose gear on the bus is not designed to rotate at all when it retracts.....other than to say it will rotate to the centered position. If it isn't centered when the gear lever is raised, it will not retract.

A350
 

JimNtexas

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I was wondering if it was a good idea for people to be wandering around under the airplane right after it stopped.

It seemed to me that there must have been some chance that what was left of the nose gear might fail, dropping the nose to the pavement, and squishing a bunch of rubberneckers in the process.
 

Rogue5

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Old report on similar Cactus incident:

On February 16, 1999, at 1602 Eastern Standard Time, an Airbus A-320-231, N628AW, operated by America West Airlines as flight 2811, received minor damage when it landed at Port Columbus International Airport (CMH), Columbus, Ohio, with the nose wheels rotated 90 degrees. There were no injuries to the 2 certificated pilots, 3 flight attendants and 26 passengers. Visual meteorological conditions prevailed for the scheduled passenger flight which had departed from Newark (EWR), New Jersey, about 1404. Flight 2811 was operated on an instrument flight rules flight plan conducted under 14 CFR Part 121.

According to statements from the flight crew, flight 2811 was uneventful until the landing gear was lowered prior to landing at CMH. After the landing gear was extended to the down-and-locked position, the flight crew received indications of dual landing gear control and interface unit (LGCIU) faults.

The flight crew entered into a holding pattern and attempted to troubleshoot the faults; however, they were unable to determine the source of the problem. The flight crew then prepared for a landing at CMH, with nosewheel steering and thrust reversers inoperative due to the faults. During the final approach, at the flight crew's request, the control tower performed a visual check of the landing gear, which revealed that the nosewheels were rotated about 90 degrees.

The flight crew then initiated a missed approach and declared an emergency. The cabin crew was notified of an impending emergency landing, and the cabin and passengers were prepared for the landing. The captain initiated the approach, and described the touchdown as soft. The airplane stopped on the 10,250-foot-long runway with about 2,500 feet of runway remaining. Damage was limited to the nose landing gear tires and rims.

The captain reported that after landing, he noticed smoke was drifting up on the right side of the airplane. He said he attempted to contact the control tower and confirm if a fire was present, but was unable due to frequency congestion. He then initiated an emergency evacuation using the left and right side overwing exits.

A review of the air/ground communications, as recorded by the Columbus Air Traffic Control Tower, did not reveal a congested frequency when the emergency evacuation was initiated.

According to Airbus, nose wheel steering was hydraulically actuated through either the cockpit tiller and/or the rudder pedals.

A post-incident visual inspection of the nose landing gear assembly revealed no anomalies. The steering control module was replaced, and a subsequent functional check of the nosewheel steering was successful.

The steering control module was a sealed unit, opened only during overhaul, with no specified overhaul time, and had accumulated 3,860 hours since last overhauled on March 3, 1998. It was shipped to Messier-Bugatti, the manufacturer, and examined under the supervision of the French Bureau Enquetes Accidents (BEA). The examination revealed that the external hydraulic O-ring seals on the steering control module's selector valve were extruded (distorted out of the seal's groove). A small offset was found in the steering control valve.

Airbus further reported that while the offset would have been measurable, it would not have been noticeable under normal operations. Additionally, during landing gear extension, the brake and steering control unit (BSCU) would have been energized and hydraulic pressure would have been directed toward the steering servo valve. The BSCU would have then commanded a small rotation of the nose wheel to check for proper movement. Any disagreement between the commanded position and actual position of the nose wheel would have deactivated the nose wheel steering. However, if hydraulic pressure had bypassed the steering control valve, there would have been continued pressurization to the servo valve, and because of the servo valve's inherent offset, in-flight rotation of the nose wheels.

Procedures existed for removal of hydraulic pressure from the steering control module. However, once the nosewheel strut had deflected 90 degrees, the centering cam would have been rotated to a flat area, and would have been incapable of overriding the 3,000 PSI hydraulic system, and returning the nose wheels to a centered position.

Documents from Airbus indicated there have been three similar incidents in which A320 airplanes landed with the nose wheels rotated about 90 degrees. Examination of the steering control modules on two of the airplanes revealed extrusion of the selector valve's external seals similar to that found on N628AW. Airbus had attributed the extrusion failures to the lack of a backup seal or the effects of aging on the seals. As a result of these incidents, Airbus issued Service Bulletin (SB) A320-32-1197 on October 8, 1998, to recommend replacement of the external seals on the steering control module's selector valve on A320 and A321 airplanes within 18 months of the SB's issuance.

At the time of the incident, neither the French Direction General de l'Aviation Civile (DGAC), or the Federal Aviation Administration (FAA), had adopted the service bulletin as an airworthiness directive. The operator was not required to comply with the service bulletin, and had not complied with it.

On March 24, 1999, the DGAC issued Airworthiness Directive (AD) 1999-124-129(B) to require compliance with the SB. On December 17, 1999, the FAA issued AD 99-23-09 which was based upon the French AD, with a 12 month time of compliance for modification of the nose wheel steering control valve.
 

rvsm410

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Finally an answer..

A350 said:
The nose gear on the bus is not designed to rotate at all when it retracts.....other than to say it will rotate to the centered position. If it isn't centered when the gear lever is raised, it will not retract.

A350
Thanks A350....that is all I wanted to know....as usualy I heard or saw somewhere in this world of mis information that the Bus Gear normally rotated...I thought that was very strange only because I am sure I would have noticed this watching this acft durning takeoffs...
 

HawkerF/O

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I was curious about that as well. Since nose wheels don't really have a snubber until they are in the well, a rotating wheel turned 90 degrees from the direction of travel would put tremendous stress (Gyro) on that motor and would not seem to make a lot of sense, but stranger things have happened! I am eager to read the final report and see what is causing this problem. Thanks for the original post.
 
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