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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 ...
121.5 MHz is the civilian aircraft emergency frequency or International Air Distress frequency. It is used by some civilian emergency locator beacons; however, the Cospas-Sarsat system no longer monitors the frequency. 243 MHz for NATO military aircraft emergency frequencies
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.
A discrete transponder code (often called a squawk code) is assigned by air traffic controllers to identify an aircraft uniquely in a flight information region (FIR). This allows easy identification of aircraft on radar. [6] [7] Codes are made of four octal digits; the dials on a transponder read from zero to seven, inclusive. Four octal digits ...
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.
Mayday is an emergency procedure word used internationally as a distress signal in voice-procedure radio communications. It is used to signal a life-threatening emergency primarily by aviators and mariners, but in some countries local organizations such as firefighters , police forces, and transportation organizations also use the term.
A serious aircraft system failure, that requires an immediate route or altitude change [22] An engine failure in a multi-engine aircraft where the aircraft is still able to maintain altitude; 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.
Before 1 October 2002 it was known as the Global High Frequency System (GHFS). HFGCS stations tend to operate in the aviation bands clustered around 5, 6, 8 and 11/12 MHz, although other frequencies are in use. The primary HFGCS voice frequencies are 4724.0 kHz, 8992.0 kHz, 11175.0 kHz, and 15016.0 kHz.