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 use, also known as
Military Air Distress (MAD),
NATO Combined Distress and Emergency Frequency,
[1] or
UHF Guard.
[1] Earlier
emergency locator transmitters (ELTs / EPIRBs) used the guard frequencies to transmit. As of February 1, 2009 satellite monitoring of the 121.5 and 243 MHz ELT (EPIRB) frequencies ceased, whereas an additional band from 406.0 to 406.1 MHz is now used exclusively by modern emergency locator transmitters (EPIRB).
[1]
Guard frequencies can be used for distress calls,
such as Mayday calls, and urgency calls, such as Pan-pan calls.
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