Squawk. Explain like I'm five

I understand a squawk code is a pre-flight number assigned by ATC. Is the number simply another feature of plane radar ID? Why do I occasionally get a “7x00” alert? Thanks

ATC assigns a squawk code to an aircraft that they are talking to. The squawk code gets manually input into the aircraft’s transponder.

Secondary radar sends out Mode A (“squawk”) interrogations that ask for the squawk code; the transponder responds with whatever was set. The radar now knows a position and an associated squawk code.

Now ATC can match the radar return from the aircraft to the particular aircraft that they’re talking to based on the squawk code. Without the squawk code the radar return would only tell you “there’s some aircraft at the location, but I don’t know which one”.

There are special squawks for special situations (1200 for VFR in the US, 7500/7600/7700 for emergencies) which aren’t directly assigned by ATC.

(If you were to design the system from scratch today, then I’m not sure you’d end up with squawk codes as more recent Mode S transponders have other ways of identifying aircraft. But the system has evolved over time, which is why it’s the way it is)

The Mode A system that returns the squawk code dates back to the immediate post WW2 period and arose from military IFF systems. It’s pretty amazing that it hasn’t been pensioned off by now, but the aviation industry has always been somewhat conservative about these things - Mode S has been around since the early 80s and it’s only relatively recently that the majority of aircraft use it. It was only made compulsory in Europe at the end of last year.

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Great, thanks. Would a pilot manually change the squawk code to “7xxx” in the case of an emergency? Or, why would we see a 7xxx code?

As said the 7xxx series are indeed intented for safety issues.

The codes are

Squawk code 7500 Hijacking in progress
Squawk code 7600 Radio comms failure
Squawk code 7700 Emergency declaration

These code have to be put in manually by the pilot and in turn it will alert the emergency services and airtraffic control on the situation

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