Washington (CNN) -- A company dispatcher who was seated in the cockpit jump seat as Southwest Airlines Flight 4013 landed at the wrong Missouri airport has been placed on paid leave pending the outcome of the investigation, the company told CNN on Tuesday.
Investigators will want to know whether the dispatcher distracted the pilot as the Boeing 737 and its 124 passengers approached the airport, a source familiar with the investigation told CNN.
The pilots of Sunday's flight, which departed from Chicago's Midway airport, remain on paid leave.
The dispatcher will give investigators another source of information and open up another line of questions surrounding the landing at M. Graham Clark Downtown Airport near the resort community of Branson, Missouri.
An industry official said the Federal Aviation Administration, which is conducting its own investigation, has reviewed the actions of air traffic controllers at Branson Airport and "indicate that there appears to be no controller issue."
The Southwest dispatcher was authorized by the company to fly in the jump seat -- which is a fold-down seat in the cockpit.
Under an FAA regulation known as the "sterile cockpit" rule, pilots must restrict all conversations to flying-related matters when planes are taking off and landing. The rule is intended to keep distractions from interfering with the flight.
The FAA, along with the National Transportation Safety Board and Southwest remained largely silent Tuesday about the investigation.
However, the pilots have been given routine drug and alcohol tests. Results of the tests have not come back, said NTSB spokesman Keith Holloway. The NTSB plans to interview the pilots and the dispatcher in the coming days, Holloway said.
Also, the NTSB is reviewing the airplane's cockpit voice recorder and flight data recorder. Preliminary information is expected to be released when it becomes available.
Investigation officials acknowledged that the 737 had returned to service, suggesting that the investigation was focused on human factors and not mechanical malfunctions.
An NTSB spokesman said officials planned to interview the pilots, but it was unknown if interviews had been scheduled.
The official familiar with the incident said it was certain that the pilots would be asked if the third person in the cockpit had somehow distracted them. A review of cockpit voice recordings may also answer that question. Southwest said the flight's captain had worked for the airline for 14 years and the first officer had been with the company for 12.
FAA air traffic controllers and company employees are sometimes permitted to ride in cockpit jump seats so they can learn about life "on the other side of the frequency," as it's sometimes called.
At one point, after a government investigation disclosed widespread abuse of the privilege by air traffic controllers, the FAA halted the program. But it was resurrected a few years ago under tighter controls.
No one was hurt in Sunday's landing on the airport's relatively short runway. But it was memorable. One passenger said it was "one of the hardest landings I ever experienced."
The plane stopped about 500 feet from the end of a runway, said Chris Berndt, the Western Taney County Fire District fire chief and emergency management director. If the plane had overshot the end of the runway it could have tumbled down an embankment and onto U.S. Highway 65.
Southwest said Monday it has reached out directly to apologize to each passenger, refund their tickets and provide future travel credit.