More than three years after Air France flight 447 crashed into the Atlantic Ocean, it has remained unclear why its captain, who was on a scheduled break, took more than a minute to return to the cockpit, despite his co-pilot's calls for help, black box recordings show. Now, questions have arisen if the captain was traveling with an off-duty flight attendant.

In Wednesday night's Nightline episode, two independent sources told ABC News that Capt. Marc Dubois, 58, was traveling socially with an off-duty Air France flight attendant, who has been identified as Veronique Gaignard. The flight hit hard weather in the early morning hours of June 1, 2009, after leaving Rio de Janiero for Paris.

The flight attendant had not been a part of the investigation because the agency was not interested in the captain's private life, Jean-Paul Troadec, the director of BEA, the French authority investigating the crash, told ABC News. Troadec added that he did not think Dubois's alleged relations with Gaignard aboard the plane would have played a role in the accident.

According to the report, just before the plane hit the thunderstorm, Dubois left the cockpit to take a scheduled nap. It is not clear if he and the flight attendant were together at the time of the emergency. The (U.K.) Telegraph reported that Dubois was married, with two adult children. It wasn't immediately clear if they had been interviewed for Nightline's story.

After the plane flew into the storm, its pitot tube, which tells the pilot the aircraft's air speed, failed, likely after ice crystals formed on it, according to the BEA. This would have disengaged the auto-pilot system, shifting control back to the pilot, according to BEA officials,  who are still investigating the crash.

According to tapes, First Officer Cedric Bonin, 32, with fewer than 5,000 flight hours, was at the controls but lacked experience at such high altitude. When Bonin pulled the nose up, the plane stalled, according to the report.

The black box tapes recorded the final cockpit conversation, moments before the plane crashed into the sea. The tapes indicates Dubois returned to the cockpit in time to ask what was happening.

I don't know what's happening, one of the co-pilots replied.

I have a problem ... I have no more displays, Dubois said.

The last statement heard in the recordings was Bonin asking if the plane was going down. 

The pilots never gained control of the Paris-bound plane, which crashed into the Atlantic Ocean, killing all 228 passengers and crew.

The BEA plans to release the final results of investigation into the crash on July 5. ABC News said Air France declined an interview request, pending the report's release.