The Germanwings tragedy that took the lives of 148 passengers and crew of the Lufthansa subsidiary would not likely happen in a U.S. carrier. That's because American air carriers have a two-crew rule.

That means when one of the pilots have to leave the cockpit to go to the toilet, for instance, a flight attendant or another pilot or flight crew must enter the cockpit to ensure there are always two persons inside, explains Denverpost.

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Cockpit doors have a keypad from the outside where a pilot enters a code to re-enter the cockpit. However, a person inside the cockpit could override the code or manually lock the door from inside, which appears to be what happened to the pilot of the ill-fated Germanwings flight.

Greg Feith, former senior investigator for the National Transportation Safety Board, said, "That regulation was implemented and standardized in the U.S. But it wasn't adopted as an international standard. Some airlines do it, but many don't."

After the Thursday crash of the Germanwings in a remote region in France, Air Canada, Lufthansa, Air Berlin, budget carrier Easyjet and Norwegian Air Shuttle said they would adopt the two-crew rule in the cockpit to avert a repeat of what co-pilot Andres Lubitz did.

Making the cockpit inaccessible from the outside was the result of the September 11, 2001 terror attack in New York City to prevent unauthorized entry to the cockpit and protect it from penetration using small firearms and fragmentation devices like grenades.

USA Today reports that Lubitz had illness which he did not disclose to Germanwings. A search of his home in Dusseldorf found torn-up medical certificates for the day of his flight which indicated an existing ailment and corresponding medical treatment. While the German prosecutors did not state the nature of the ailment, German media said it was depression.

TagsGermanwings, plane crash, andreas lubitz