A hijacking happens when passengers overflow into the cockpit from the cabin.
Oh no! A little kid has been invited to have a look! Passenger overflow! Hijacking!
His attempt at solution isn't as cringe worthy, if one overlooks the reasoning. Separating the cabin from the pilots is a way of preventing hijacking that has been attempted, but it has problems. Notably if the pilots get acute medical emergency or indeed if the pilot steer the plane into the ground.
Some ten years ago a french pilot locked out his second and ran the plane into the ground. For increased safety the after 911 the door to the cabin could only be opened from the inside.
@mountainriver Also of note: the Helios Airways Flight 522 disaster. (Loaded 737 crashed, everybody killed … because of a locked cockpit door: plane depressurized and pilots' oxygen failed, cabin crew—inc. a pilot—were unable to gain cockpit access in time to save the plane before it ran out of fuel and crashed.) https://en.wikipedia.org/wiki/Helios_Airways_Flight_522
Door wasn't locked and had nothing to do with the crash. In fact a flight attendant managed to get into the cockpit and turn the plane from a populated part of Athens, likely saving lives shortly before it fully crashed
The plane simply never pressurized and literally as the co-pilot realized what was happening hypoxia took them and the captain, all because a switch could turn pressurization into a manual override and there was no warning before takeoff that it was that way
German pilot, and crash in France, not French pilot. Second pilot locking out the captain, not the other way around. Otherwise my memory seem to have served.