What's happening in the cockpit? Questions after Germanwings crash

PHILADELPHIA (WPVI) -- A location aviation expert said an important rule was being broken when the Germanwings jet crashed in the French Alps.

Aviation analyst and attorney Arthur Wolk says the configuration of that plane, the Airbus 320, requires two people in the cockpit at all times.

We now know the pilot of the flight left the cockpit during the flight, leaving co-pilot Andreas Lubitz alone.

Investigators say it now appears Lubitz locked the pilot out of the cockpit and intentionally crashed the airliner, killing 150 people

"It's my view that at no time should a single person be in charge of an airplane that's certified for two," he said.

Wolk says it is a requirement that is routinely broken by foreign carriers. Here in the United States, it's the law.

"Not only is it the law in this country, it is the accepted procedure everywhere," said Wolk.

Lufthansa, the parent company of Germanwings, says the pilot did nothing wrong by temporarily leaving the cockpit.

Wolk says the co-pilot was too inexperienced to fly alone, and an emergency could happen at any time.

"There are emergencies that can occur that a single pilot can't handle. Why would you leave him in that airplane by himself? It makes no sense."

Lufthansa says the co-pilot who deliberately flew the plane into a mountain had been properly trained and had undergone psychological evaluation.

Wolk says companies may require it, but the law here doesn't require pilots to have psychological exams before they fly.

And even if they were, it wouldn't protect against a sudden death wish.

"There have been instances in the past where that same vetting process has not been successful. For the same reason we find that certain people who appear to be doing well all of a sudden snap and do some bizarre and harmful things," said Wolk.

Wolk says the only possible insurance is having more than one person in the cockpit at all times.