Squawk Codes Explained: How Air Traffic Control Identifies Aircraft

Have you ever wondered how the Air Traffic Control (ATC) identifies and tracks hundreds of aircraft on the radar simultaneously? The answer is Squawk Codes. 

Squawk Codes act as digital number plates which make identification of aircraft easy and also avail the ATC with non-verbal communications.

What are Squawk Codes?

A Squawk Code is a four-digit octal code input into an aircraft's transponder to enable the ATC identify and track it on a ground-based Secondary Surveillance Radar (SSR).

Digits range from 0-7 making 4,096 possible codes (0000-7777).

There are 3 kinds of Squawk Codes which include;

• Assigned codes:  unique discrete code assigned to an aircraft by the ATC under its control for precise tracking.
• Emergency codes: Recognized universally indicating specific emergencies.
• Standard VFR code: 1200 for aircraft operating under VFR(Visual Flight Rules) in the USA.

History of Squawk Codes

The Squawk Codes originated during the World War II where the radar systems couldn't distinguish between a friendly and an enemy aircraft leading to the formation of IFF (Identification Friend or Foe) system.

 This system was codenamed "Parrot" then the word "Squawk" to represent the process of communication which has stuck till to date.

The two-way communication system was set up using a transponder where the ATC puts out a request for an aircraft to identify itself. If the aircraft identified itself with a code then it's identified as a friendly which is not the case today.

How Aircraft Transponders work.

Transponder short for Transmitter-Responder is an electronic wireless device that gives out radio signals when it receives a similar signal telling it to. 

In Aviation, a transponder is a Radio Frequency Identification Device (RFID) installed in an aircraft to send signals to the ATC radar systems in order to identify, detect location, altitude of an aircraft and support safety and emergency responses during flight.

• The pilot is given a Squawk Code for their flight before take off.
• Pilot switches on the transponder and input the code as instructed.

• Then the ATC confirms that the code has been set and that they can track the aircraft while in flight.

On the radar screens, the ATC will be able to identify the specific flight by seeing the flight's Squawk code. This enables the ATC notice the traffic around the aircraft and help it avoid any accidents, staying out of restricted airspaces and also getting back the flight on track incase its lost.

Emergency Squawk Codes Explained

Squawk 7700- General Emergency

This is the Mayday Squawk code used in a serious situation requiring immediate assistance. These situations can be mechanical/technical and medical emergencies for example an engine failure, fires, depressurization.

Squawk 7600- Radio Failure

This is the code that informs the ATC of the loss of a two-way radio contact. ATC makes adjustments to ensure the aircraft lands safely

In this kind of emergency, the pilot should proceed to their intended destination following the flight plan.

Squawk 7500- Hijacking/Unlawful Interference

Discreetly signals a hijacking which alerts the ATC and security agencies on the ground and most times indicates that the pilot is no longer in control of the aircraft or being forced to change course.

Flight jets are usually dispatched to escort the aircraft to a base.

Types of Transponder Modes

Mode A

Primarily used for identification. it allows the ATC to see the aircraft on radar and identify it.

Mode C

Adds pressure altitude information to identification which is derived from the aircraft's altimeter.

Required for flying in Types A, B, C and international Airspaces.

Mode S

Provides enhanced surveillance data aircraft identification and position information to the ATC which includes altitude data in precise increments. This is crucial for safe separation between aircraft.

Primarily used in areas of dense traffic and airspace with no ATC radar coverage.

 SQUAWK IDENT

All modes have an IDENT button which is short for "identify".

It briefly highlights your aircraft on the ATC's radar when pressed. This button shouldn't be pressed unless asked by the ATC.

 STANDBY MODE

Keeps the transponder powered on but not actively transmitting data. The active signal transmission can be activated when needed. Switched on after landing and taxiing off the runway.

Why Squawk Codes are Important.

Aircraft Identification: The assigned discrete codes given uniquely identify each aircraft in the airspace on the ground-based SSR. Each Squawk code on the ATC screen is an aircraft. 

Support emergency and safety response: The emergency Squawk codes reserved for emergence situations strictly signals how the ATC prioritizes providing immediate assistance to an aircraft in distress.

Support enhanced surveillance: Some modes of operation go beyond just giving position, they also provide the pressure altitude with enhanced situational awareness and traffic conflict detection avoiding mid-air collisions.

In conclusion, with the advancement of technology modern transponders support ADS-B (Automatic Dependent Surveillance-Broadcast), relies on satellite navigation systems such as GPS which provide near to constant updates of an aircraft's position, heading and speed.