121.5 MHz
121.5 MHz is a radio frequency of the Mobile Air Service (R) (117.975–136 MHz) in the VHF frequency range. The amplitude modulation operating mode is used for sending and receiving . In the field of air traffic control , it is also referred to as a guard .
Definition of the International Telecommunication Union
According to Article 593 of the Implementing Regulations for the Radio Service of the International Telecommunication Union , the following regulation is binding for Region 1 (Europe, including the territory of the Federal Republic of Germany):
- “In the 117.975 MHz - 136 MHz frequency range, the 121.5 MHz frequency is the emergency frequency for the aeronautical service and, if necessary, the 123.1 MHz frequency is the auxiliary frequency to the 121.5 MHz frequency; Mobile radio stations of the mobile maritime radio service may operate under the conditions of the mobile radio service stipulated in Articles 38 and N 38 (Malaga-Torremolinos 1973, VO-Funk) on these frequencies in emergencies and security cases ”.
National characteristics
121.5 MHz is an emergency frequency and is used to handle radio communications for aircraft in emergencies . In contrast to the maritime service , where defined frequencies are used to make an emergency call, this frequency is rarely used to make an emergency call. Mobile aeronautical radio stations are usually already in contact with a ground radio station on a radio frequency. An emergency call should therefore be placed on this frequency. There is no obligation to eavesdrop on the frequency for aircraft.
If there are several radio receivers on board, it is strongly recommended to use a receiver for constant monitoring of the emergency frequency 121.5 MHz. Aeronautical stations of the aeronautical mobile service constantly monitor this frequency generally. Many ELT (emergency location transmitter) or EPIRB (emergency position-indicating radiobeacon) transmit a radio alarm signal on this frequency.
If an aircraft does not report on the specified radio frequency, it is called up by the air traffic control, by other aircraft that serve as a relay station or by the military air surveillance on 121.5. If an aircraft is intercepted by military means, an attempt is made to establish contact via 121.5.
In the past, the frequency was tapped by satellites. This service was discontinued in 2009. Nowadays satellites listen on the frequency 406 MHz for broadcasts from emergency beacons . Modern emergency radio beacons continue to send a signal on this frequency in addition to the 406 MHz frequency. This function, known as homing , is used for localization in close proximity by SAR forces. The frequency has a special meaning for interceptors. Aircraft are addressed by them on this frequency. In the military aeronautical radio sector there is a frequency with a comparable function, the frequency 243 MHz.
Web links
Individual evidence
- ↑ Frequency range allocation plan for the Federal Republic of Germany and international allocation of the frequency ranges 9 kHz – 400 GHz; 1994; issued by the BMPT; BAPT order no. 5010311 001-1; Page 86, 117.975 - 136 MHz MOBILE AIRCRAFT SERVICE (R).
- ↑ www.icao.int SARPS about Emergency frequency
- ↑ www.aea.net The End Is Near for 121.5 MHz
- ↑ www.cospas-sarsat.int The International Cospas-Sarsat System has ceased satellite processing of 121.5 / 243 MHz beacons on February 1, 2009. All beacon owners and users should replace their 121.5 / 243 MHz beacons with 406 MHz beacons as soon as possible .