Bill Hemmer spoke to commercial pilot Robert Mark this morning after the shocking news that a co-pilot deliberately crashed an airliner into the French Alps earlier this week. 

What We Know About Co-Pilot Who Deliberately Crashed Airliner in France

It emerged last night that the older, more experienced Germanwings pilot had been locked out of the cockpit during the plane's final eight-minute descent. 

This morning, a French prosecutor said it appears that 28-year-old co-pilot Andreas Lubitz locked the door and manually initiated the plane's descent.

After the 9/11 attacks, cockpit doors were reinforced to the point where they were meant to withstand gunfire or an explosion. The FAA said in 2002 in its announcement of the new standards that the the doors should be "sufficient to minimize penetration of shrapnel from small arms fire or a fragmentation device."

As you can see on this video produced by Airbus, there are three switch positions to control the locking door: unlock, normal, and lock.

In normal mode, the door is locked, but a crew member can get in by entering a code on a touchpad. This would allow for emergency entry in the event that a pilot became incapacitated. 

Unlocked mode would allow someone to enter. For example, if one pilot left to use the restroom, the second pilot would flip the switch to allow him to re-enter.

The locked mode, which officials believe was engaged on the doomed flight, means that the system ignores attempts to open the door via the touchpad.

If a hijacker hypothetically forced a crew member to give up the entry code, the pilot or pilots behind the door could then keep the door from opening.

Mark emphasized that there is absolutely no way to override that or to break through the reinforced door once it is in the locked mode.

"It was meant to keep the bad guys out and it's done a really good job of that. Unfortunately, sometimes when you fix one problem, you create another. And what we've seen here is it also kept the good guys out," said Mark. 

Watch the analysis above. And stay tuned to Fox News for continuing updates on this developing story. 

What We Know About Co-Pilot Who Deliberately Crashed Airliner in France