There have been at least seven cases in which the front wheels on Airbus A320s became stuck in a sideways position, forcing pilots to make emergency landings.
No one was hurt in any of the landings, the latest of which occurred Wednesday night in front of a national television audience when a JetBlue plane touched down
in Los Angeles amid smoke and sparks as the front tires disintegrated.
The incidents, unnerving to be sure, are nonetheless considered anomalies and have not prompted federal authorities to take action beyond ordering airlines to follow Airbus instructions for replacing rubber seals on the gear.
With about 2,500 Airbus A320s in operation worldwide, the number of incidents involving jammed nose gear is not significant, Federal Aviation Administration spokesman Greg Martin said Thursday.
"It's a safe aircraft," he said.
Wednesday's emergency started soon after takeoff from Burbank, Calif., when the JetBlue A320 pilot noticed a caution light indicating a problem with the landing gear. He circled past the Long Beach Airport's control tower, where flight controllers saw that the nose wheel hadn't retracted and was twisted out of alignment.
The plane flew in circles for three hours to burn off fuel, then landed safely at Los Angeles International Airport, balancing on its back wheels as it rolled down the center of the runway.
The National Transportation Safety Board sent a team of investigators to determine what happened.
"Last night's incident concluded exactly as Airbus expected it would," Airbus spokeswoman Mary Anne Greczyn said. "Flight crews are trained to handle such situations and aircraft are designed to withstand such landings."
The A320 family _ which includes the A318, A319 and A321 _ has a somewhat unusual landing gear that rotates before retracting into the fuselage.
"It's definitely not the most common way," said Chuck Eastlake, aerospace engineering professor at Embry-Riddle Aeronautical University in Daytona Beach, Fla. "The reason is that the ability of the nose wheel to rotate 90 degrees introduces the possibility of failure, exactly like what we saw."
In contrast, Boeing aircraft landing gear all move straight up and down.
The A320 landing gear is moved through hydraulic pressure, when fluid is pumped into a valve, which moves a piston. Rubber seals called O-rings are used to prevent the hydraulic fluid from leaking.
But if the hydraulic fluid leaks, the piston won't work right, Eastlake said.
That's what happened in at least two previous incidents. Airbus said the landing gear got stuck because of problems with the seals, and told airlines they should replace the seals on A320 and A321 aircraft.
That message came after a Feb. 16, 1999, incident in which an America West A320 landed at Port Columbus International Airport in Columbus, Ohio, with its nose wheels sideways.
The NTSB said in that case that the problem was caused by rubber seals that got pushed out of their groove, which jammed the landing gear.
On Nov. 1, 2002, a JetBlue flight from Buffalo, N.Y., made a safe emergency landing at John F. Kennedy International Airport in New York. Just 19 days later, a United Airbus A319 turned back after takeoff from O'Hare International Airport in Chicago because the pilot couldn't retract the landing gear.
The NTSB found that the latter incident was probably caused by improper assembly of the landing gear's shock absorber assembly.
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On the Net:
National Transportation Safety Board: http://www.ntsb.gov
Federal Aviation Administration: http://www.faa.gov
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