Transponder squawk codes every pilot should know

The emergency codes, the VFR conspicuity codes in Europe and the US, and what modes A, C and S mean.

The short answer

7700 means emergency, 7600 means radio failure and 7500 means unlawful interference. For VFR flight without a specific code, squawk 7000 in most of Europe and 1200 in the United States.

Other codes you may meet

• 7000: VFR conspicuity code in most ICAO states
• 1200: VFR code in the United States and Canada
• 2000: used in some regions when entering from an area without secondary radar
• Local listening squawks: some countries assign a code that tells ATC you are monitoring a given frequency

Modes A, C and S

Mode A sends only the four digit code. Mode C adds pressure altitude. Mode S adds an individual aircraft address and more data, and is required in much of European airspace. Always switch to ALT, not just ON, so controllers and collision avoidance systems see your level.

Changing codes

When setting a new code, avoid passing through the emergency codes on the way. Many modern transponders let you type the whole code before it takes effect, which removes the problem.