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U.S. air-safety investigators are looking into a mechanical failure that caused the nose of an Allegiant Airlines jet to rise off the ground prematurely before takeoff, defying the crew’s attempts to push it down.

Pilots abruptly halted their roll on the runway at 138 miles (222 kilometers) an hour to regain control of the Boeing Co. MD-83 in Las Vegas on Aug. 17, the Federal Aviation Administration said. Allegiant blamed a fault in the elevator, the part of the tail that helps an aircraft to climb or descend.

“That is a very big deal,” John Goglia, a former member of the National Transportation Safety Board who worked as an airline mechanic, said in an interview. “At very minimum, they would have had control problems. In a worst-case scenario, they would have been unable to control it. It could have been a disaster.”

Primary flight controls on airliners are so critical to safe operations that they must be designed to essentially never fail. Manufacturers such as Boeing must certify to the FAA that the odds of a malfunction involving the elevators and other flight controls are less than one in a billion.

The loss-of-control issue last week also was reported to the NTSB, which investigates aircraft accidents. Allegiant, a unit of Allegiant Travel Co., inspected all its MD-80-type jets, which make up about 70 percent of the fleet, after the incident.

“I don’t know that I have ever heard of one doing that,” John Cox, a former airline pilot who is now president of consultant Safety Operating Systems, said in a telephone interview. “That’s how rare it is.”

Federal Requirements

Because of the potential severity of a flight-control failure, federal regulations require that a second qualified mechanic inspect and sign off on any maintenance performed on the elevators, Goglia said. He worked on the MD-80 and its predecessor models for 30 years.

The incident adds to safety issues raised at Allegiant, a Las Vegas-based carrier that focuses on flights to leisure destinations. The FAA opened an investigation last month into a plane getting so low on fuel that the pilot said he needed to make an emergency landing.

Last week’s episode involved Flight 436, which was bound for Peoria, Illinois, with 158 passengers and six crew members.

Began Liftoff

The jet began to lift off from the runway before it was moving fast enough for a normal takeoff, and the front of the plane stayed up even as a pilot adjusted the controls in a way that should have kept the nosewheel on the runway, according to an incident report filed by the airline to the FAA.

The pilots then aborted the takeoff, according to the FAA.

Allegiant said an inspection found that a device that moves one of the plane’s two elevators had become disconnected. The plane was repaired and put back into service.

All of the airline’s jets from the MD-80 family were checked out “to ensure the flight control systems in those aircraft were functioning properly before returning them into service,” said Kimberly Schaefer, an Allegiant spokeswoman. “All aircraft were found to be in working order.”

A mechanical failure of a related system at the tail of another MD-83 led an Alaska Airline Group Inc. plane to crash into the Pacific Ocean north of Los Angeles in 2000, killing all 88 people aboard.

(Updates with comment from former NTSB member in third paragraph.)