MEOLANS-REVELS, France, March 25 (UPI) -- The notion that a pilot may have been left alone in the cockpit of Germanwings Flight 9525 shortly before it crashed in the French Alps is virtually unheard of, an aviation specialist told the Los Angeles Times Thursday.
The Airbus A320 crashed Tuesday with 150 people aboard, including two babies and 16 high-schoolers, who are all presumed dead.
Wednesday, the New York Times cited a senior military official as saying the recovered cockpit voice recorder picked up "very smooth, very cool" conversation between the two pilots during the first part of the flight. One of the pilots is later heard leaving the cockpit, and then again as he pounded on the door trying to get back in. Moments later, the jetliner began a rapid eight-minute descent from 6,8000 feet into a mountain.
"You can hear he is trying to smash the door down," the source said. "At the very end of the flight, the other pilot is alone and does not open the door."
University of Southern California aviation instructor and security expert Glen Winn told the Los Angeles Times, in a report Thursday, that scenario is highly unusual -- and even possibly a violation of airline security protocol.
"Procedurally, something was very wrong," he said. "You ask any pilot, they'll tell you the same thing ... They don't leave a person alone in the cockpit. They don't do it. Nobody does that."
Aviation expert Peter Goelz said essentially the same thing, telling CNN that if the pilot couldn't get back up front it's a "shocking" revelation that could indicate a medical emergency or something more sinister. Winn agrees, saying the cockpit tape may suggest the pilot in the cockpit was incapacitated or that he intentionally put the aircraft into a descent.
Winn also noted that aviation security protocols, mandated by Congress after 9/11, almost assuredly would have been in place at Germanwings -- an aviator owned by Lufthansa, the largest airline in Europe that shares standardized aviation procedures with U.S. carriers.
Standard procedure when a pilot leaves the cockpit, he said, is for a flight attendant to wait inside with the other pilot and open the door for the departed pilot when he returns.
"That's nothing secret. Everybody knows," Winn said.
Even if a flight crew member didn't follow this procedure, the Times article notes, an operating manual for the Airbus A320 says flight attendants can enter a two-to-seven digit code into a keypad on the outside of a locked cockpit door to open it.
According to U.S. investigators, an intentional descent with a lone pilot at the controls has happened before. In 1999, Egypt Air Flight 990 crashed into the Atlantic off the Massachusetts coast, killing all 217 on board. The NTSB ruled that the flight's first officer, left by himself in the cockpit, initiated a sharp dive that saw the jet plummet into the sea from 14,600 feet in 36 seconds.
The NTSB didn't specify a motive for the pilot's actions, but a former co-worker speculated that the first officer may have been exacting revenge on an airline official who was aboard the flight. Egyptian investigators, though, disagreed -- concluding that the crash was the result of a mechanical failure.
Sounds from the audio file indicate that flight 9525 was flying right up until it crashed and did not explode in midair, investigators said.
Officials with the French Bureau of Investigations and Analysis (BEA) told The Guardian they were "optimistic" they could locate the second black box, called the flight data recorder, which records how the aircraft performs in-flight.
"We are combing the site, and we will find the flight data recorder, which is built to resist a severe crash," BEA spokesman Rémi Jouty said. "I am confident we will find out what happened."
Wednesday, the U.S. State Department told ABC News that three U.S. citizens were aboard the aircraft. Two were identified by family members as mother and daughter Yvonne Selke and Emily Selke. The State Department has not yet identified the third American on the plane.
Officials said, in addition to the Americans, the passenger and crew list included 45 Spaniards, 67 Germans, two Australians and several British nationals. Among the dead are two teachers and two German opera stars.
The plane was en route to Barcelona, Spain, from Düsseldorf, Germany. Lufthansa Vice President Heike Birlenbach said the company is treating the crash as an accident. The plane left the airport 30 minutes late, but there was little more authorities could say. French Prime Minister Manual Valls said "no hypothesis" could be ruled out.
Lufthansa will operate two flights, one from Barcelona and one from Dusseldorf, so that relatives of the victims can visit the crash site, BBC News reported Thursday. The family members will arrive in Marseilles and then travel to Meolans-Revels in the French Alps by vehicle. BBC News reported that 14 Spanish relatives are traveling by bus because they don't want to fly.
"The French people are here shoulder to shoulder with you during this ordeal," France's president, Francois Hollande, said. "Everything will be done to find, identify and hand back to the families the bodies of their loved ones."