FAA controllers were taught to anticipate a specific sign or communication from a plane before declaring a hijacking76 in progress. A pilot might surreptitiously key in the transponder code “7500,” a universal distress signal, which would automatically flash the word hijack on the flight controller’s green-tinted radar screen. If the problem was mechanical, a pilot could key in “7600” for a malfunctioning transponder, or “7700” for an emergency. Otherwise, a pilot under duress could speak the seemingly innocuous word “trip” during a radio call when describing a flight’s course. An air traffic
...more
