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The aircraft emergency frequency (also known in the USA as Guard) is a frequency used on the aircraft band reserved for emergency communications for aircraft in distress.The frequencies are 121.5 MHz for civilian, also known as International Air Distress (IAD), International Aeronautical Emergency Frequency, [1] or VHF Guard, [1] and 243.0 MHz—the second harmonic of VHF guard—for military ...
This frequency is also used for direction finding (DF). 155.160 MHz; 172.5 MHz— U.S. Navy emergency sonobuoy communications and homing use. This frequency is monitored by all U.S. Navy ASW aircraft assigned to a SAR mission. 282.8 MHz— Joint/combined on-the-scene voice and DF frequency used throughout NATO
Military aircraft also use a dedicated UHF-AM band from 225.0 to 399.95 MHz for air-to-air and air-to-ground, including air traffic control communication. This band has a designated emergency and guard channel of 243.0 MHz. [2] [8] Radio aeronautical navigation aids use other frequencies.
4.2 Emergency codes. 5 Transponder ... a radio-frequency interrogation. Aircraft have ... off the skin of the aircraft. Primary radar determines range and bearing to ...
The civilian aircraft frequency for voice distress alerting is 121.5 MHz. Military aircraft use 243 MHz (which is a harmonic of 121.5 MHz, and therefore civilian beacons transmit on this frequency as well). Aircraft can also signal an emergency by setting one of several special transponder codes, such as 7700.
Instrument Flight Rules (IFR) flight below 18,000 ft ASL when no other code has been assigned. [7] ICAO: Non-discrete mode A code reserved use in mode S radar/ADS-B environment where the aircraft identification will be used to correlate the flight plan instead of the mode A code. [1] US: Used exclusively by ADS-B aircraft to inhibit mode 3A ...
Despite the switch to 406 MHz, pilots and ground stations are encouraged to continue to monitor for transmissions on the emergency frequencies, as most 406 MHz beacons are required to be equipped with 121.5 "homers." Furthermore, the 121.5 MHz frequency remains the official global VHF aircraft voice distress frequency.
Pan-pan calls may be made on the aircraft emergency frequency, but they are more often made on the frequency already in use, or another appropriate frequency. ICAO Annex 10, Volume V, § 4.1.3.1.1 states "the emergency channel (121.5 MHz) shall be used only for genuine emergency purposes". However, ICAO member states can deviate from this rule.