Airline captains don’t have an “open door policy, and there’s a good reason for that. Aside from the obvious terrorist and crazy passenger threats, airline pilots realize they face another adversary: treacherous interruptions.

In 1974 an Eastern Airlines flight carrying seventy-eight passengers and four crew members crashed in dense fog during an instrument approach into Charlotte, killing seventy-one. The National Transportation Safety Board determined that the flight crew’s lack of altitude awareness and poor cockpit discipline caused the crash.