In the 1950s, when I was a flight attendant, commercial passenger planes had three people in the cockpit able to fly the plane: the captain, copilot, and navigator. Even when the plane was on automatic pilot, the navigator monitored its position and altitude. Had a navigator been on board the tragic Germanwings flight, he could have let the captain in, and the two could have taken over the controls and subdued the copilot in time to prevent the horrible crash.
