- 1 Introduction
- 2 Transponder in real life
- 3 Transponder code allocation
- 4 See also
- 5 Reference
- 6 Author
Transponder in real life
The ATC radar sends an interrogative 1030 MHz radio frequency pulsed signal. The aircraft answers on the 1090 MHz radio frequency with another pulsed signal. After decoding and measuring the delay of answer, the transmitted signal is used on ATC radar to identify the aircraft (code and/or call sign) and displays relevant information (azimuth, altitude, speed, flight path).
Several different RF (Radio Frequency) communication protocols have been standardized for civilian aviation transponders. Depending on the interrogation mode, transponders can provide identification code, aircraft position, pressure altitude, call sign and other information.
- Mode A : equipment transmits an identifying code only,
- Mode C : provides identifying code and aircraft pressure altitude,
- Mode S : (for 'Selective') provides multiple information formats to a selective interrogation (data exchange), including the call sign - it is designed to help avoiding over-interrogation and to allow automatic collision avoidance.
A transponder switch usually has several positions:
- OFF : The "OFF" position will power down the transponder.
- STBY: The “STBY” position will power the transponder and make it ready for operation (warming up).
- ON : The “ON” position (MODE A) will only send primary information to the radar (code and position).
- ALT: The “ALT” position (MODE C or S) will additionally transmit altitude information.
- TA : The “TA” position will provide traffic advisory.
- TA/RA : The “TA/RA” position will provide traffic advisory resolution.
All mode A, C, and S transponders include an IDENT button, which activates a special function known as IDENT (short for identify) in order to help air traffic controllers locate an aircraft.
Squawk codes are four-digit octal numbers. The dials on a transponder read from 0 to 7 inclusive.
Transponder code allocation
In IVAO, SSR (Secondary Surveillance Radar) transponder codes can be allocated by divisions through coordination with regional air navigation agreements and taking into account the code allocation practiced in adjacent divisions.
- 7700 : Emergency code
- 7600 : Radio failure code
- 7500 : Hi-jack code
Here are the descriptions and the usage of some codes attribution:
Transponder 7700 : emergency
The pilot shall continue to use the specified code unless otherwise advised by ATC. If the pilot is facing a simple pan or failure, this code shall not be used.
An ATC can request a pilot to squawk 7700 if he declares an emergency or distress situation (MAYDAY).
Transponder 7600 : radio failure
This code is mainly used when a pilot is facing serious technical problems with his connection that cannot permit voice and text communication or for training/examination purposes.
A controller, who notices a communication failure code, will determine the extent of the failure by instructing SQUAWK IDENT or to change the code. With that operation, if it is determined that the aircraft receiver is functioning, further control of the aircraft will be continued using code changes or IDENT transmission to acknowledge receipt of clearances.
Transponder 7500 : hi-jacking
“Special operation including simulation of terrorism and act of wars are prohibited.Although armed conflicts do exist in the real world, we do not allow the simulation of any form of aggression or violence on the IVAO network.”
Non-controlled VFR code
Depending on local regulations, non-controlled VFR codes can change.
The most frequently codes used are:
- 1200 : USA and Canada standard squawk code
- 7000 : Europe VFR standard squawk code
- 2000 : ICAO standard squawk code
Non-controlled IFR code
This is a list of some other codes available:
- 0000: this code shall not be used. It is a non-discrete code. It is usually displayed on IVAO pilot software in case of some specific technical problems.
- 7777: Non-discrete code used to test transponders and to check correctness of radar stations
- 74xx: these codes are sometimes used for NATO special operations
- ICAO Documentation 4444 - Air Traffic Management - 16th Edition 2016 - Chapter 8.5
- VID 150259 - Creation
- VID 150259 - Wiki integration
DATE OF SUBMISSION
- 20:42, 23 January 2022
- This documentation is copyrighted as part of the intellectual property of the International Virtual Aviation Organisation.
- The content of this documentation is intended for aviation simulation only and must not be used for real aviation operations.