AIRMET
Encyclopedia
An AIRMET, or Airmen's Meteorological Information, is a concise description of weather phenomena that are occurring or may occur along an air route that may affect aircraft
safety. Compared to SIGMET
s, AIRMETs cover less severe weather: moderate turbulence
and icing, surface winds of 30 knots, or widespread restricted visibility.
AIRMETs are broadcast on the ATIS
at ATC
facilities, and are referred to as Weather Advisories. AIRMETs are valid for six hours. NOTE: The definition has changed and no longer says "light aircraft"; Airmets are intended for all aircraft.
There are three types of AIRMET, all identified by a phonetic
letter: S (Sierra), T (Tango), and Z (Zulu). http://www.faa.gov/ATpubs/AIM/Chap7/aim0701.html#7-1-6
For an authority to issue an AIRMET, applicable conditions must be widespread. "Widespread" means that the applicable area covers at least 3000 square miles. Because conditions across the forecast period can move across the area, it is possible that only a small portion of the area is affected at any time.
AIRMET’s are routinely issued for six hour periods beginning at 0145Z during Central Daylight Time and at 0245Z during Central Standard Time. AIRMETS are also amended as necessary due to changing weather conditions or issuance/cancellation of a SIGMET.
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
safety. Compared to SIGMET
SIGMET
SIGMET, or Significant Meteorological Information, is a weather advisory that contains meteorological information concerning the safety of all aircraft. There are two types of SIGMETs, convective and non-convective...
s, AIRMETs cover less severe weather: moderate turbulence
Turbulence
In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time...
and icing, surface winds of 30 knots, or widespread restricted visibility.
AIRMETs are broadcast on the ATIS
Automatic Terminal Information Service
Automatic Terminal Information Service, or ATIS, is a continuous broadcast of recorded noncontrol information in busier terminal areas. ATIS broadcasts contain essential information, such as weather information, which runways are active, available approaches, and any other information required by...
at ATC
Air traffic control
Air traffic control is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other...
facilities, and are referred to as Weather Advisories. AIRMETs are valid for six hours. NOTE: The definition has changed and no longer says "light aircraft"; Airmets are intended for all aircraft.
There are three types of AIRMET, all identified by a phonetic
NATO phonetic alphabet
The NATO phonetic alphabet, more accurately known as the NATO spelling alphabet and also called the ICAO phonetic or spelling alphabet, the ITU phonetic alphabet, and the international radiotelephony spelling alphabet, is the most widely used spelling alphabet...
letter: S (Sierra), T (Tango), and Z (Zulu). http://www.faa.gov/ATpubs/AIM/Chap7/aim0701.html#7-1-6
- AIRMET SIERRA (Mountain obscuration or IFR) ceilingsCeiling (cloud)- ICAO :The height above the ground or water of the base of the lowest layer of cloud below 6000 meters covering more than halfthe sky.- United Kingdom :...
less than 1000 feet and/or visibility less than 3 miles affecting over 50% of the area at one time; extensive mountain obscuration
- AIRMET TANGO (Turbulence) moderate turbulence, sustained surface winds of 30 knots or more
- AIRMET ZULU (Icing) moderate icing, freezing levels
For an authority to issue an AIRMET, applicable conditions must be widespread. "Widespread" means that the applicable area covers at least 3000 square miles. Because conditions across the forecast period can move across the area, it is possible that only a small portion of the area is affected at any time.
AIRMET’s are routinely issued for six hour periods beginning at 0145Z during Central Daylight Time and at 0245Z during Central Standard Time. AIRMETS are also amended as necessary due to changing weather conditions or issuance/cancellation of a SIGMET.
External links
- http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/6A07EFAA9A68C1A8862576C70052E9E5?OpenDocument - FAA Advisory Circular Website (link to AC 00-45G "Aviation Weather Services" where the definition is found)