An AIRMET, or Airmen's Meteorological Information, is a concise description of weather phenomena that are occurring or may occur (forecast) along an air route that may affect
aircraft
An aircraft is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters the force of gravity by using either Buoyancy, static lift or by using the Lift (force), dynamic lift of an airfoil, or in ...
safety. Compared to
SIGMET
SIGMET, or Significant Meteorological Information (AIM 7-1-6), is a severe weather advisory that contains meteorological information concerning the safety of all aircraft. Compared to AIRMETs, SIGMETs cover more severe weather.
Types
There a ...
s, AIRMETs cover less severe weather: moderate
turbulence
In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...
and icing, sustained surface winds of 30 knots or more, or widespread restricted visibility.
Types
AIRMETs are broadcast on the
ATIS at
ATC facilities, and are referred to as Weather Advisories. AIRMETs are valid for six hours.
[ICAO Annex 3 Chapter 7] 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
Phonetics is a branch of linguistics that studies how humans produce and perceive sounds, or in the case of sign languages, the equivalent aspects of sign. Linguists who specialize in studying the physical properties of speech are phoneticians. ...
letter: S (Sierra), T (Tango), and Z (Zulu).
* AIRMET SIERRA (Mountain obscuration or IFR)
ceiling (cloud), ceilings 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 greater, and/or non convective low−level wind shear.
*AIRMET ZULU (Icing) Moderate icing and provides freezing level heights.
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. AIRMETs are routinely issued for six-hour periods beginning at 0145Z during Daylight Saving Time and at 0245Z during Standard Time. AIRMETS are also amended as necessary due to changing weather conditions or issuance/cancellation of a SIGMET.
Dissemination And Structure
Most AIRMET dissemination is done graphically now, but computer systems use a text-based AIRMET, which is identical in structure to a SIGMET, with the only difference being that the "SIGMET" identifier in the
First Line is replaced by the three type identifiers listed above.
See also
*
SIGMET
SIGMET, or Significant Meteorological Information (AIM 7-1-6), is a severe weather advisory that contains meteorological information concerning the safety of all aircraft. Compared to AIRMETs, SIGMETs cover more severe weather.
Types
There a ...
*
PIREP
References
External links
*
*
*
* Graphical representation of AIRMETs can be found at: https://www.aviationweather.gov/. Select the G-AIRMET checkbox for "Graphical AIRMET".
Aviation meteorology
Weather warnings and advisories
Aviation publications
{{Aviation-stub