AIRMET (Airman's Meteorological Information) is an aviation weather advisory. It warns pilots of moderate weather hazards that may affect smaller aircraft and general aviation operations.
How It Works#
The National Weather Service issues AIRMETs for the contiguous United States on a fixed schedule. They are published every six hours, with updates issued between cycles when conditions change. Each advisory is valid for up to six hours, except Sierra AIRMETs covering mountain obscuration, which can extend to twelve hours.
AIRMETs come in three types, each named with a phonetic designator:
- Sierra covers instrument flight rules (IFR) conditions and mountain obscuration. IFR conditions mean ceilings below 1,000 feet or visibility below 3 statute miles.
- Tango covers moderate turbulence, sustained surface winds above 30 knots, or low-level wind shear.
- Zulu covers moderate icing and the freezing level (the altitude where the temperature drops to 0°C).
Each AIRMET specifies the affected geographic area, altitude range, and time period. Pilots can retrieve them through official preflight weather services such as 1800wxbrief.com or the Aviation Weather Center.
AIRMETs differ from SIGMETs (Significant Meteorological Information) in severity. SIGMETs address severe or extreme conditions. AIRMETs address moderate conditions that are still operationally significant, especially for light aircraft.
Example in Aviation#
A student pilot planning a cross-country flight from Denver to Albuquerque checks the weather before departure. She finds an active AIRMET Tango covering her route, citing moderate turbulence below 12,000 feet MSL (mean sea level, measured from a standard reference point). She also sees an AIRMET Sierra indicating IFR conditions over the mountain passes along her route.
She briefs her instructor. Together they decide to delay the flight by two hours and file at a higher altitude to stay above the turbulence layer. The AIRMETs gave them the information they needed to make that call.
Why It Matters#
AIRMETs are especially relevant to general aviation pilots flying light, single-engine aircraft. These aircraft are more vulnerable to moderate turbulence and icing than larger transport-category planes. Ignoring an active AIRMET can mean flying into conditions that exceed the aircraft's or pilot's capabilities.
Checking for AIRMETs is a core part of a thorough preflight weather briefing. Pilots operating under visual flight rules (VFR) or instrument flight rules (IFR) should review all active AIRMETs covering their route and altitude before every flight.
Key Takeaways#
- AIRMETs warn of moderate weather hazards affecting general aviation aircraft.
- Three types exist: Sierra (IFR/obscuration), Tango (turbulence/wind), and Zulu (icing).
- They are issued every six hours and are valid for up to six hours.
- AIRMETs are less severe than SIGMETs but still operationally significant.
- Always check for active AIRMETs during your preflight weather briefing.