CHI03IA027

The airplane landed with the nose wheels turned 90 degrees to the direction of travel. The flight crew was unable to retract the landing gear after takeoff. They received the L/G SHOCK ABSORBER FAULT and AUTO FLT A/THR OFF messages on the electronic centralized aircraft monitoring (ECAM) system. In addition, they had a Nose Wheel Steering message on the landing gear ECAM page. Unable to rectify the problem, the captain elected to return to land at ORD. The captain reported that he did not have any problem controlling the airplane during the landing. During the landing roll, he was informed by the control tower that there were sparks coming from the nose gear. The airplane stopped on the runway and the passengers were deplaned. Post-incident inspection revealed the nose landing gear (NLG) wheels were turned 90 degrees to the left, both of the tires were blown, and the left side tire rim was ground down to the axle. The right side tire rim was nearly ground down to the axle. The incident occurred on the fourth flight following a maintenance "C" check where the dynamic seals inside the nose landing gear (NLG) shock absorber had been replaced. The maintenance was performed by a contract facility. Inspection and teardown of the nose gear revealed the shock absorber had been assembled and installed in the airplane incorrectly during the C-check. This resulted in the anti-rotation lugs on the shock absorber, not being properly seated in the back plate slots. Following this incident, the back plate manufacturer has redesigned the back plate (waiting manufacturer and DGAC approval), the operator has revised their job instruction cards for disassembly and assembly of the NLG shock absorber, and the aircraft manufacturer has revised the Aircraft Maintenance Manual.

On November 21, 2002, at 1006 central standard time, an Airbus Industrie A319-131, N804UA, operated by United Airlines (UAL) as flight 603, received minor damage when it landed on runway 04R (8,071 feet by 150 feet, asphalt) at the O'Hare International Airport (ORD), Chicago, Illinois. The airplane landed with the nose landing gear (NLG) wheels turned 90 degrees to the direction of travel. There were no injuries to the 2 pilots, 3 flight attendants, and 77 passengers on board. The 14 CFR Part 121 flight was being conducted in visual meteorological conditions and an instrument flight rules flight plan was filed. Flight 603 departed ORD at 0918, en route to Los Angeles, California.

The captain reported that they received a "L/G shock absorber fault" on the upper display of the electronic centralized aircraft monitoring (ECAM) system when the crew attempted to retract the landing gear after takeoff. He reported they placed the gear handle in the down position after which time they also received the "AUTOFLIGHT" ECAM message and they lost use of the autopilot, autothrust, and flight directors. The captain reported that he instructed the first officer to fly the airplane while he accomplished the ECAM action items. He instructed the first officer to inform air traffic control of their problem and to request that they be able to stay near the airport in case they needed to return. The captain stated he then contacted dispatch and the system aircraft maintenance controller (SAMC) for further guidance. The captain reported the ECAM landing gear page, on the lower display, showed all three landing gear were down and locked, and the gear doors were closed, along with an amber nose wheel steering message. UAL reported that during the flight SAMC instructed the crew to interrogate the Centralized Fault Display System (CFDS), which revealed the "Nose Wheel Steering" fault. After troubleshooting the gear problem with SAMC, it was determined that the airplane should return to ORD. The captain reported that given the ECAM messages that they had, he was concerned that there would not be any nose wheel steering during the landing roll. SAMC informed the captain that if they did not have nose wheel steering it might be recovered during the landing roll when the nose strut was compressed.

The captain reported he took over flying the airplane and prepared for a landing on runway 04R. He stated the landing was smooth and the nose wheel felt normal on the wet runway. However, during the landing roll, the control tower informed him that sparks were visible from the nose gear. He reported that as the airplane slowed, they noticed a noise and vibration prior to the airplane stopping on the runway just short of the "Q" turnoff. The captain reported he informed the passengers to remain seated until he was able to assess the condition outside the airplane. He stated the Fire Department reached the airplane within one or two minutes. He was informed that there were no hazards outside the airplane and the passengers were deplaned.

Post-incident inspection revealed the NLG wheels were turned 90 degrees to the left. Both of the tires were blown. The left side tire rim was ground down to the axle. The right side tire rim was nearly ground down to the axle. There was no damage present on the airplane except for the NLG assembly.

NLG Shock Absorber Description and Operation

The manufacturer of the NLG shock absorber is Messier-Dowty. The shock absorber is a double-acting, oleopneumatic type with no separator piston.

The shock absorber assembly consists of two sections: a stationary inner cylinder (piston), which is mounted inside the shock strut assembly, and a sliding tube, which is the lower portion and contains the wheel axle. The upper portion of the inner cylinder contains anti-rotation lugs. During installation of the shock absorber, the anti-rotation lugs are aligned in slots on a backplate, which is mounted inside the top of the shock strut. A nut is then installed to secure the inner cylinder of the shock absorber/gear assembly to the backplate.

The bottom of the inner cylinder contains the lower cam. The upper part of the sliding tube contains the upper cam. This cam is held in place by eight dowel pins retained by a bushing and a retaining ring. During gear extension and retraction, the sliding tube extends down and the two cams engage, centering the nose wheel. When the strut is compressed on the ground, the cams are separated and the nose wheel is free to move for on ground steering.

Teardown Inspection

When the NLG was removed from the airplane, it was determined that the anti-rotation lugs at the top of the shock absorber were not properly seated in the backplate, which indexed and bolted to the inside of the shock strut assembly.

The shock absorber assembly was shipped to the UAL Maintenance facility in San Francisco, California, where it was disassembled and inspected on December 5, 2002.

The shock absorber assembly was disassembled using the Job Instruction Cards (JIC) provided by UAL. These were the same JICs used when the strut was assembled during recent maintenance.

This teardown revealed the upper centering cam had been rotated 20 - 30 degrees when it was installed in the inner cylinder. With this condition, in order for the upper cam to mate properly with the lower cam, the sliding tube was rotated 20 to 30 degrees in relation to the aircraft centerline. In order for the axle to be perpendicular with the aircraft centerline when installed, the position of the anti-rotation lugs were rotated 20 - 30 degrees. This resulted in the anti-rotation lugs at the upper end of the strut not being properly engaged in the backplate slots.

Recent Maintenance

A heavy maintenance visit, C-check, on N804UA was completed on November 20, 2002. This maintenance was performed by a contract Federal Aviation Administration (FAA) Certified, Part 145 Repair Station.

The NLG dynamic seal was replaced during the maintenance. In order for the seals to be replaced, the shock absorber assembly was removed was removed from the airplane and the sliding tube was removed from the inner cylinder. The seals were replaced, the shock absorber was reassembled, and reinstalled in the aircraft.

Although the maintenance was performed by a contract facility, UAL JICs were used. The assembly tasks on the job cards were derived from the FAA-Approved Airbus Aircraft Maintenance Manual (AMM).

The airplane flew one non-revenue ferry flight and two revenue flights prior to the incident takeoff. The airplane had accumulated a total of 9 hours of flight time between the maintenance and the incident.

UAL reported they had performed about 60 NLG dynamic changes in the past. The contract maitnenance facility had previously performed six NLG dynamic seal changes. The mechanic who performed the dynamic seal change on the incident NLG shock absorber had performed this job two times prior to the assembly for N804UA. The first time was with a trainer and the second time was on his own.

Additional Incidents

On November 1, 2002, an Airbus A320, being operated by JetBlue landed at the John F. Kennedy International (JFK) Airport, New York, New York, with its NLG turned 90 degrees. This airplane had come out of maintenance where the NLG dynamic seal was replaced approximately 3 days prior to the incident. The airplane had flown 15 cycles and 23 hours between the completion of the maintenance and the incident. The investigation into this incident revealed the same findings as were found on N804UA. The upper centering cam on the inner cylinder had been mis-installed. This resulted in the anti-rotation lugs not being perpendicular to the axle and consequently the lugs were not properly seated in the backplate slots.

Messier-Dowty reported that there have been two additional incidents involving the