Two United Airlines A320 planes that skidded off runways in recent months had crossed wiring in their main landing gear, a spokesman for the National Transportation Safety Board said Monday.
Investigators have not concluded what the cause was and are continuing to look into both incidents, NTSB spokesman Peter Knutson said.
United Airlines confirmed the finding and said three Airbus A320s in all were found to have the faulty landing-gear wiring, which is believed to caused wheels to lock.
The most recent incident occurred Feb. 25 when a United flight with 125 people aboard slid off the runway after landing in Jackson Hole, Wyoming, ending up in 3 feet (a meter) of snow. No one was seriously hurt, although one passenger sprained a wrist while trying to open an emergency exit.
Four months earlier, a United A320 briefly veered off a runway at Chicago's O'Hare International Airport, taking out some runway lights and causing two minor injuries. United said the third miswired plane was not involved in an accident.
The airline since has inspected its entire fleet of 97 A320s and informed its mechanics, pilots and flight attendants of the incidents and the corrective steps it is taking, spokeswoman Megan McCarthy said.
"Our primary responsibility is the safety our customers and our employees, and there is no obligation we take more seriously," she said.
The incidents come amid a growing debate over the maintenance of U.S. commercial planes.
The Federal Aviation Administration recently ordered maintenance records at all domestic airlines checked. The FAA was under fire for its handling of missed safety inspections at Southwest Airlines Co.
Airlines have been outsourcing more of their maintenance work to vendors overseas.
Addressing the issue, 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."
