March 31 (Bloomberg) -- UAL Corp.'s United Airlines found crossed landing-gear wires that may have caused two Airbus SAS A320 jets to skid off runways, becoming at least the fourth major carrier under U.S. scrutiny over maintenance.

The National Transportation Safety Board and officials with United, the world's second-largest airline, are trying to learn whether the wiring mistake was made by mechanics or occurred in manufacturing and then was missed during testing.

``The NTSB has confirmed that wires in the landing gear of both of the A320s involved in the accidents were cross- connected,'' agency spokesman Peter Knudson said yesterday in an e-mail. ``We have not yet determined the probable cause.''

The inquiry expands the roster of airlines with maintenance work under U.S. review. Regulators proposed a $10.2 million fine for Southwest Airlines Co. this month over missed inspections, and American Airlines and Delta Air Lines Inc. grounded jets last week while complying with a government directive.

UAL rose 34 cents to $21.53 at 5:20 p.m. in New York Stock Exchange composite trading.

A United A320 veered from a runway into a snow bank Feb. 25 at Jackson Hole, Wyoming, the NTSB said on its Web site. On Oct. 9, an A320 left the runway and hit airport lights after landing at Chicago's O'Hare International. No one was seriously injured.

Like other commercial jets, the A320 is designed to minimize the risk of skidding on landing. The crossed wires may have overridden the normal braking procedure to guard against a skid, Knudson said. The twin-engine jet's main gear touches down first, followed by the nose wheel.

The safety board hasn't recommended that the FAA require checks to determine the extent of any runway skidding involving the planes, Knudson said.

Studying Skid Prevention

United, based in Chicago, is evaluating ``the antiskid functional test effectiveness,'' spokeswoman Megan McCarthy said. ``All of our maintenance work, whether performed in the U.S. or abroad, by United employees or partners, follows our FAA-approved maintenance program.''

Airbus, based in Toulouse, France, recommends maintenance procedures that include ``a process to verify that the wiring is properly aligned,'' spokesman Clay McConnell said in an e-mail. ``We are confident that adherence to the Airbus procedures will ensure that no aircraft re-enters service with improperly aligned wiring.''

The Chicago Tribune reported on the landing-gear wiring earlier yesterday.

Airline maintenance has drawn increased attention from regulators and Congress after the Federal Aviation Administration proposed a record $10.2 million fine against Southwest for missed inspections for fuselage cracks.

Congressional Hearing

The House Transportation and Infrastructure Committee, chaired by Representative James Oberstar, a Minnesota Democrat, plans a hearing April 3 on the Southwest issue and whether regulators have gotten lax in maintenance oversight.

The FAA, following criticism from Oberstar and labor unions, conducted special audits at more than 100 airlines to see how they complied with a sample of 10 maintenance directives. The FAA completed the initial audits March 28 and may reveal what it found before Oberstar's hearing.

AMR Corp.'s American and Delta canceled at least 734 flights, stranding thousands of passengers, during two days of disruptions that ended March 28 as they worked to comply with a FAA directive for properly attaching wiring sleeves to the Boeing Co. MD-80 model planes.

To contact the reporters on this story: Nancy Kercheval in Washington at nkercheval@bloomberg.net; John Hughes in Washington at Jhughes5@bloomberg.net

Last Updated: March 31, 2008 17:43 EDT