RENEE MONTAGNE, HOST:
The investigation into the crash of that Germanwings flight in the French Alps quickly answered the question of what happened. And that answer has led to an even greater mystery. Why would the copilot apparently lock the pilot out of the cockpit while he deliberately crashed a plane filled with 149 passengers and crew into a mountainside? Investigators came to that chilling description of what happened based primarily on what they heard on the plane's cockpit voice recorder. They're still looking for the other black box, the flight data recorder. NPR's David Schaper reports on how investigators hope to use both.
DAVID SCHAPER, BYLINE: French authorities stunned the world in announcing that the Germanwings co-pilot appears to have intentionally crashed a plane into a French mountainside. Marseille prosecutor Brice Robin says sounds recorded from the cockpit in the flight's final minutes indicate the pilot was locked out and pounding on the cockpit door while the co-pilot didn't say a thing.
(SOUNDBITE OF ARCHIVED RECORDING)
BRICE ROBIN: Nothing - he never - no word, no word, no word during the ten last minutes.
SCHAPER: But how accurate can that audio be?
ANTHONY BRICKHOUSE: That recorder doesn't record what possibly happens. Listening to that recording, you hear exactly what was happening in the cockpit.
SCHAPER: Anthony Brickhouse is an aviation safety investigator, formerly with the NTSB, and now teaching at Embry-Riddle Aeronautical University. He says boom mics, when keyed, record the voices of each pilot and, in this case, even the normal breathing of the co-pilot, indicating he was conscious and not in medical distress. And a cockpit-area microphone or cam is always recording, picking up just about every sound.
BRICKHOUSE: The conversations between the pilots and maybe air traffic control, the pilots speaking to each other, you would be listening for warning sounds in the cockpit. You would be listening for any noises that you would expect to be heard or noises that you would not expect to be heard.
SCHAPER: And Brickhouse says the pilot banging on the door is clearly one of those sounds that is a big clue. But he says plane crash investigators never rely on just one piece of evidence. So he says one of the most important remaining pieces is the other black box, the flight data recorder.
BRICKHOUSE: So that they can corroborate what they've heard on the cockpit voice recorder with the physical parameters that were actually recorded on the flight data recorder.
SCHAPER: The crash of flight 9525 is raising questions about whether efforts to secure the cockpit door have gone too far. John Hansman, professor of aeronautics at MIT, says post-September 11 safety measures have turned the cockpit into a fortress.
JOHN HANSMAN: There's no way you can break into the cockpit and particularly not in the seven or eight minutes that apparently they had.
SCHAPER: There are also calls internationally to require that at least two crew members remain in the cockpit at all times, as the FAA requires in the U.S. Aviation expert Ewan Wilson, author of a book on Malaysia Airlines Flight 370, which disappeared over the Indian Ocean last year, goes even further with his recommendations.
EWAN WILSON: The introduction of more robust mental health review and analysis across all airlines and the introduction of a third person in the cockpit.
SCHAPER: International aviation authorities issued a statement Thursday indicating they will likely consider changes to cockpit and flight crew safety protocols in the wake of the Germanwings crash. David Schaper, NPR News. Transcript provided by NPR, Copyright NPR.
