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) or VHF Guard, and 243.0 MHz—the second harmonic of VHF guard—for military use, also known as Military Air Distress (MAD) or UHF Guard. Earlier emergency locator transmitters (ELTs) used the guard frequencies to transmit, but an additional frequency of 406 MHz is used by a more modern emergency locator transmitter.
In the United States, the emergency frequency is monitored by most air traffic control towers, FSS services, national air traffic control centers, military air defense and other flight and emergency services, as well as by many commercial aircraft. The notice to airmen FDC 4/4386 requires "…all aircraft operating in United States National Airspace, if capable, shall maintain a listening watch on VHF GUARD 121.5 or UHF 243.0."[1]
In the UK, 121.5 MHz is monitored by the Royal Air Force Distress and Diversion cells (known as "D&D") at the London Terminal Control Centre and the Shanwick Oceanic Control, from a nationwide network of antennas. Depending on the aircraft's altitude and location, the personnel in the centres may be able to use triangulation to determine its exact position which can be useful to the pilot if the aircraft is lost or "temporarily unsure of position".
Useedit
A Swiss Air Force F/A-18 Hornet fighter with the order STBY 121.50 written on its external tank
Both guard frequencies can be used by any aircraft in distress or experiencing an emergency and in addition it can be used by air traffic control to warn aircraft if they are about to fly into restricted or prohibited airspace.
Guard frequencies can be used for distress calls, such as Mayday calls, and urgency calls, such as Pan-pan calls.
Aircraft will also be contacted on 121.5 MHz when intercepted by air defence aircraft, to ask for identification and intentions and to pass on instructions.
Misuseedit
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".
A misuse of the frequency can result in punishment. In the United States, Federal Communications Commission (FCC) rules prohibit false distress calls and superfluous communications. If the FCC Enforcement Bureau identifies an individual breaking these rules, they can be subject to a fine of up to $19,246 for a single violation and up to $144,344 for an ongoing violation. FCC may also confiscate radio equipment and file for criminal charges.[2]
In the United Kingdom, pilots may make "practice PAN" or "training fix" calls.[3][4] Practice Mayday calls are not permitted.[5]
Locating beaconsedit
Modulation of a radio beacon of distress
Transmission of a distress beacon on 121.5 MHz and 243 MHz
Older emergency locator transmitters transmit on 121.5 MHz in case of impact. Newer ELTs transmit on 406 MHz, with a low power beacon on 121.5 MHz for local homing. Satellites listen for the signals and alert local personnel to the emergency, and the beacon allows search and rescue to find the scene of the accident faster. Beacons operating at 406 MHz are encoded, allowing the vessel of origin to be determined and false alarms to be quickly verified. Satellite support for the 121.5 MHz–only versions was discontinued in early 2009.[6][7]
^"Emergency Position Indicating Radiobeacon (EPIRB)". U.S. Coast Guard.
External linksedit
Wikimedia Commons has media related to 121,5 MHz.
April 10, 2024
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This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Aircraft emergency frequency news newspapers books scholar JSTOR August 2009 Learn how and when to remove this template message 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 or VHF Guard and 243 0 MHz the second harmonic of VHF guard for military use also known as Military Air Distress MAD or UHF Guard Earlier emergency locator transmitters ELTs used the guard frequencies to transmit but an additional frequency of 406 MHz is used by a more modern emergency locator transmitter Contents 1 History 2 Monitoring 3 Use 3 1 Misuse 4 Locating beacons 5 See also 6 References 7 External linksHistory editThe choice of 121 5 MHz was made by ICAO in conjunction with ARINC and the ITU citation needed Monitoring edit nbsp Cessna radio on 121 5 standbyIn the United States the emergency frequency is monitored by most air traffic control towers FSS services national air traffic control centers military air defense and other flight and emergency services as well as by many commercial aircraft The notice to airmen FDC 4 4386 requires all aircraft operating in United States National Airspace if capable shall maintain a listening watch on VHF GUARD 121 5 or UHF 243 0 1 In the UK 121 5 MHz is monitored by the Royal Air Force Distress and Diversion cells known as D amp D at the London Terminal Control Centre and the Shanwick Oceanic Control from a nationwide network of antennas Depending on the aircraft s altitude and location the personnel in the centres may be able to use triangulation to determine its exact position which can be useful to the pilot if the aircraft is lost or temporarily unsure of position Use edit nbsp A Swiss Air Force F A 18 Hornet fighter with the order STBY 121 50 written on its external tankBoth guard frequencies can be used by any aircraft in distress or experiencing an emergency and in addition it can be used by air traffic control to warn aircraft if they are about to fly into restricted or prohibited airspace Guard frequencies can be used for distress calls such as Mayday calls and urgency calls such as Pan pan calls Aircraft will also be contacted on 121 5 MHz when intercepted by air defence aircraft to ask for identification and intentions and to pass on instructions Misuse edit 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 A misuse of the frequency can result in punishment In the United States Federal Communications Commission FCC rules prohibit false distress calls and superfluous communications If the FCC Enforcement Bureau identifies an individual breaking these rules they can be subject to a fine of up to 19 246 for a single violation and up to 144 344 for an ongoing violation FCC may also confiscate radio equipment and file for criminal charges 2 In the United Kingdom pilots may make practice PAN or training fix calls 3 4 Practice Mayday calls are not permitted 5 Locating beacons edit nbsp Modulation of a radio beacon of distress source source Transmission of a distress beacon on 121 5 MHz and 243 MHz Problems playing this file See media help Older emergency locator transmitters transmit on 121 5 MHz in case of impact Newer ELTs transmit on 406 MHz with a low power beacon on 121 5 MHz for local homing Satellites listen for the signals and alert local personnel to the emergency and the beacon allows search and rescue to find the scene of the accident faster Beacons operating at 406 MHz are encoded allowing the vessel of origin to be determined and false alarms to be quickly verified Satellite support for the 121 5 MHz only versions was discontinued in early 2009 6 7 See also editAir ground radiotelephone service Airband Distress signal Mayday Transponder aeronautics References edit FDC 4 4386 Special Notice National Airspace System Intercept Procedes PDF Federal Aviation Administration FAA FCC Investigating Misuse of 121 5 MHz Mayday Frequency National Business Aviation Association 2017 08 17 Retrieved 7 August 2023 https www raf mod uk sites raf beta assets File 95E50AF2 D570 FF5F 478C01766B2F43C8 1 pdf https www getintoflying com distress and diversion cell a practical guide to practice pan and training fix Radiotelephony Manual CAP 413 https publicapps caa co uk docs 33 CAP413 20E23 20A1 2026Nov2020 pdf Emergency Beacons NOAA Emergency Position Indicating Radiobeacon EPIRB U S Coast Guard External links edit nbsp Wikimedia Commons has media related to 121 5 MHz Retrieved from https en wikipedia org w index php title Aircraft emergency frequency amp oldid 1214808854, wikipedia, wiki, book, books, library,
