A pilot from another airline helped land a Southwest Airlines flight that left early Wednesday from Las Vegas after its captain became "incapacitated" and required medical attention, according to the airline and radio traffic data, in an episode that surprised some passengers who had no clue a pilot had fallen ill.

Southwest Flight 6013 had taken off just after 6:30 a.m. bound for Columbus, Ohio, according to the flight-tracking site FlightAware. While it was airborne, one of its pilots "needed medical attention," a spokesperson for the airline said, without giving details about the health issue.

In radio traffic archived by the website LiveATC, a person says the captain had started to feel stomach pain and then "fainted or became incapacitated" around five minutes later.

The person says the captain "came back" around 60 seconds later and was being looked after in the back of the plane. "We need to get him on an ambulance immediately," the person says.

Las Vegas resident Diane McGlinchey, who was on the flight with her husband, said Thursday that she didn't notice any panic when crew members initially went on the plane's public announcement system to ask whether medical personnel were on board.

A passenger sitting up front who said she was a nurse put on her call light to help, McGlinchey said. She said she and her husband had been at the back of the plane and didn't notice it was the pilot who needed aid, but she said they knew the ill person was with the nurse in her row.

The crew "calmly just would give us an update saying we're going to go back to Las Vegas, we have a medical emergency on board," McGlinchey said.

Meanwhile, a credentialed pilot from another airline who was on board as a passenger entered the flight deck and assisted with radio communication as the second Southwest pilot flew the aircraft, the airline.

"We greatly appreciate their support and assistance," the spokesperson said of the pilot who stepped in.

According to FlightAware, the plane returned to Las Vegas' Harry Reid International Airport at about 7:50 a.m. A Southwest spokesperson said the plane landed safely and an alternate crew took over, operating the flight to Columbus.

"We commend the crew for their professionalism and appreciate our customers' patience and understanding regarding the situation," the spokesperson said.

McGlinchey said she and her husband didn't realize it was the pilot who had had the medical emergency until after the plane landed. EMS and fire officials were already waiting, she said.

"That's when the pilot did come on and say that they were taking the captain off the plane," she said.

The other pilot from another plane happened to also be in his uniform, she added, and no one seemed anxious or worried when the flight turned around to go back to Las Vegas.

We were "very thankful that he was there," McGlinchey said of the pilot who intervened. "I'm positive that the first officer would have been able to land smoothly, but it definitely made it, I'm sure, easier for him to have someone there to do the radio part while he was landing the plane. So it went very smoothly."

Ross Aimer, the CEO of Aero Consulting Experts in California and a retired United Airlines pilot, said that commercial airline pilots undergo medical checkups every six months and that such health scares are rare.

With two pilots on every flight, the captain and the first officer are "equally qualified and trained" to operate the plane by themselves if the other becomes incapacitated, he added.

That by chance a third pilot was on board "was icing on the cake," Aimer said.

Southwest declined to comment further about the incident. It said in a statement that all of its pilots are "trained to fly as single Pilots for situations such as this one and our Pilot exhibited exceptional airmanship while in control of the aircraft."

The condition of the stricken pilot was not immediately clear.

McGlinchey said that after they got off the plane, passengers expressed concern for the ill person even before many realized it was the pilot.