What is a Squawk in Aviation?

What says “squawk” and flies in the sky?

Is it a parrot, a Cessna, or a 787?

Or all three?

Squawk is a common term used in air traffic control to describe a specific type of radio signal that comes from the plane’s transponder.

So this funny word is not just for the birds–pilots of all types of planes get to squawk, too.

What is a Transponder? How does it Work?

A transponder is a radio in your avionics stack, but it isn’t used for voice communications. Instead, it creates a signal that only air traffic control (ATC) radar systems can see. 

The primary purpose of a transponder is to help controllers pick apart all the targets on their radar scopes. When the radar sweeps the sky, radio waves bounce off the aircraft and return to the station. Those returns on the scope show that there’s a plane there, but it can’t tell much about it.

This basic radar blip is called a “primary return.” If the controller watches the primary return they can get an idea of speed and direction. But it gives no indication of the target’s altitude. Plus, all primary returns look the same, so there’s no way to tell which return belongs to which plane, beyond its location on a map. 

The transponder fixes all of these problems. First, the transponder sends a signal to the radar that contains a four-digit squawk code. For example, if the air traffic controller tells one plane to “Squawk 1234,” that number will appear on the radar scope. This more detailed target is called a “secondary return.”

What’s more, modern transponders have “Mode-C.” A Mode-C transponder has the ability to send out the plane’s pressure altitude. The controller calibrates their scope with the current altimeter setting, and all aircraft then show their altitudes. With that information, the controller can separate flights safely in three dimensions. 

History of the Transponder and the Word “Squawk”

If you think the word squawk sounds like a bird squawking, you’ve got a good idea of how the transponder came to be. 

Today’s transponder technology was first designed in World War II when radar was first implemented. Controllers needed a way to identify friend or foe (IFF), so a basic transponder was developed. If the radar hit a plane and it returned a friendly transponder code, it was a friend. If it returned a primary only–or something else–it was treated as a foe. The codename for the IFF system was “Parrot,” and the signals the planes sent out became known as squawks.

Common Transponder Terms

The transponder has been a foundational technology in air traffic control for more than half a century. ADS-B and NextGen technologies are starting to phase out traditional radar transponders in favor of satellite-based identification systems. But until the entire National Airspace System has completely transitioned, transponders will be around for the foreseeable future.

Here are a few of the most common controller requests that involve the transponder. On the pilot side, there’s not much to this little radio. But it’s a vital part of ATC communication that you should be familiar with.

Squawk XXXX, as in “Squawk 4356”

The most basic function of the transponder is to send a discreet four-number code to ATC. This positively identifies you as you. 

In instrument flying, your flight is assigned the code right at the beginning before you even get in the air. The radar system knows it, and instead of showing the four-digit code, it will display your tail number as indicated on your flight plan. 

VFR pilots are assigned codes when they request transitions through controlled airspaces, like Class B or Class C. They also get codes when they request VFR flight following. And finally, discrete transponder codes are used to identify flights crossing the ADIZ (air defense identification zone) on the national borders.

“Squawk VFR” or “Squawk 1200”

Of course, VFR pilots aren’t always talking to controllers. When in Class G or E airspace, they can operate independently without contacting anyone. In these cases, if the plane has a transponder, they set it to the standard VFR code, which is 1200. 

“Squawk IDENT” or “IDENT”

The IDENT button on the face of the transponder allows the pilot to send out a particular signal that is picked up on the controller’s radar. It doesn’t change the code or anything, but it makes your radar return flash–which draws the controller’s attention. This is handy when there are many radar returns in one area, all squawking 1200. The IDENTing aircraft will flash on the radar screen.

You might be asked to “Squawk IDENT” when you first call a control tower inbound for landing. Many Class D airports have a radar screen, but it’s not worth assigning you a code. Instead, they just want to know which radar return they’re talking to.

Another time you’ll hear it is when you first call for an IFR flight plan in the air or want to request VFR flight following. The IDENT helps the controller verify that you’re in their airspace.

Only press the IDENT button when asked, and only press it momentarily–there’s no reason to hold it down.

“Squawk Altitude” or “Stop Altitude Squawk”

Transponders have a few settings that allow them to override equipment issues. There are usually two modes–ON and ALT. The standard setting is “ALT,” which means that altitude reporting (Mode C) is active. If you accidentally set the transponder to ON, you might get asked by ATC to “squawk altitude.”

Controllers will likely start asking you to verify your altitude if your altitude reporting starts going haywire and reporting inaccurate numbers. If they discover that the transponder is in error, they may request that you “stop altitude squawk.”

Transponder Squawk Codes You Should Know

There are a handful of four-digit codes that every pilot should know. These are used every day in the National Airspace System. Never forget your transponder can communicate with ATC even when you think you can’t.

0000 — A generic code that is not assigned and should not be used.

1200 — VFR aircraft. The default code for all flights–if you aren’t asked to set anything else, you should set 1200.

7500 — Hijacking

7600 — Voice radio failure

7700 — Mayday or emergency

These last three codes, 7500, 7600, and 7700, display special notes for air traffic controllers. Controllers can set up their scopes to filter some planes off. For example, if a controller only worries about the approach area for a Class C airport, they don’t need to see the en-route traffic controlled by Center at 35,000 feet.

However, if a plane at 35,000 squawks 7700, it will light up on every controller’s scope. 

A radio failure is less dramatic, but the radar computers note it. For example, a 7600 code will show as “NORAD” on a controller’s scope. It’s important to note that a voice radio failure does not necessarily mean a complete communication failure for the pilot.For example, it’s possible you can still hear ATC but not transmit, in which case you could respond to controller requests and acknowledge with an IDENT.

What Happens When You Squawk 7500?

Squawking 7500 on your transponder sends a critical signal to air traffic control. This code means your plane is facing unlawful interference or hijacking. It’s a silent way to tell controllers you’re in trouble without alerting others on the radio.

When you squawk 7500, several things may occur:

• Fighter jets might escort your plane
• Police could be waiting when you land
• Air traffic control will keep other planes away from you
• The airport you’re heading to might shut down

Here’s what to expect if you squawk 7500:

Action	Possible Outcome
Set transponder to 7500	Alert sent to ATC
ATC receives alert	Emergency response activated
Emergency response	Fighters scrambled, airport cleared

Remember, only use this code in real emergencies. Squawking 7500 is serious business. It triggers a big response, so make sure you have a good reason before you set it.

What Happens When You Squawk 7600?

When you set your transponder to 7600, you’re telling air traffic control (ATC) that your radio isn’t working. This code is used for lost radio communication.

The impact on your flight depends on how bad the radio problem is. You might be able to hear ATC but not talk back. If this happens, ATC might ask you to “squawk ident”. This means pushing a button on your transponder that makes your plane flash on their screen.

If you can’t hear or talk on the radio, you still have options:

1. Follow loss of communication steps
2. Watch for light signals from ATC when near the airport

Remember, even without radio, you can still fly safely. Stay calm and use the tools you have. ATC knows what 7600 means and will work to keep you and others safe in the air.

What Happens When You Squawk 7700?

Squawking 7700 on your aircraft’s transponder signals an emergency situation. This code alerts air traffic control (ATC) that you’re facing a serious issue and need immediate assistance.

The 7700 code is versatile and can be used for a wide range of emergencies. Some common reasons to use this code include:

• Medical emergencies on board
• Engine failures
• Critical fuel shortages
• Collisions with birds
• Damage to the aircraft’s frame
• Severe ice buildup
• Fires
• Problems with flight controls
• Loss of cabin pressure

Remember, this list isn’t complete. You can use 7700 for any situation you consider an emergency.

When you squawk 7700, you gain more flexibility in how you operate your aircraft. You can deviate from normal flight rules if needed to handle the emergency. But keep in mind, you’ll need to explain your actions later.

After setting the code, be ready for ATC to contact you. They’ll want key details about your situation. Prepare to give them:

1. Your aircraft’s registration
2. Your current location
3. The nature of your problem
4. Where you plan to land
5. How many people are on board
6. How much fuel you have left

To help you remember what to tell ATC, use the NITS method:

N – Nature of the problem: Briefly explain what’s wrong I – Intentions: Tell them where you’re heading and what you plan to do T – Time: Let them know when you expect to land and how much fuel you have S – Special instructions: Mention any specific needs or requests

By using 7700 and following these steps, you can get the help you need quickly and safely in an emergency situation. Stay calm, communicate clearly, and focus on landing your aircraft safely.

Remembering Critical Squawk Codes: Three Simple Tricks

The Rhyme Technique

Pilots often use rhymes to recall important details. Here’s an easy rhyme for squawk codes:

“Five can’t drive” (7500 – hijacking) “Six needs a fix” (7600 – radio problem) “Seven’s not in heaven” (7700 – general emergency)

These catchy phrases help you quickly remember the right code in stressful situations.

One-Liner Memory Aid

Try this single sentence to recall all three codes:

“Hey Jack, radio’s dead, we’ve got trouble.”

This links each part to a code:

• “Hey Jack” = hijacking (7500)
• “radio’s dead” = communication failure (7600)
• “we’ve got trouble” = emergency (7700)

Just remember the codes start at 7500 and go up by 100 each time.

ICE Method

ICE is a handy acronym for the three main emergency squawk codes:

I – Interference (hijacking – 7500) C – Communication loss (7600) E – Emergency (any other – 7700)

This method is quick and easy to recall under pressure.

These three ways to remember squawk codes can help you respond correctly in tough situations. Practice them regularly so they become second nature. You never know when you might need to use them in flight.

If you’d like to know more about radar and transponders, including seeing a sketch of what a controller’s radar scope looks like, check out the FAA’s Aeronautical Information Manual,  Chapter Air Traffic Control, Surveillance Systems 4-5-1.

Be sure to subscribe to get more helpful articles for new pilots. We cover everything from holding procedures and calculating weight and balance to the best pilot gifts and aviation radios.