Quiz: When would you use this code?

What 7600 means

7600 tells ATC you've lost two-way radio communication. The AIM says that if an aircraft with a transponder loses two-way radio capability, the pilot should set the transponder to 7600 (AIM 6-4-2). Controllers see the code on radar, so they know why you aren't answering even when you can't tell them. Keep in mind you may not be in radar coverage, so the code alone doesn't guarantee anyone sees it.

When the tower goes quiet

Not hearing the tower is half of a two-way communication failure. Before you set 7600, check the simple things first: the volume, the headset plug and the frequency. Plenty of radio failures turn out to be the volume set too low or a loose plug. If the tower still can't be heard, set 7600. Then stay outside or above the Class D surface area until you know the direction and flow of traffic, tell the tower your type, position, altitude and that you intend to land, and ask to be controlled with light gun signals (AIM 4-2-13).

Why not 7700

7700 is the code for a distress or urgency condition (AIM 6-2-2).

• Engine failure: a distress condition. That calls for a Mayday and 7700.
• Sick passenger: it's up to you as PIC, but usually you'd just talk to ATC. If the passenger were in immediate danger and you were too busy to talk, 7700 would also be an option.
• Pan-pan: there's no assigned squawk for a Pan-pan. It's a radio call. If the urgency calls for a code, it's 7700.