Warning hierarchy
Warnings are operational messages for defined users, areas and validity periods. Start with who issues the message, which airspace or aerodrome it applies to, when it is valid and what action it may require.
Product roles
Aerodrome warnings support ground operations. Windshear warnings address take-off and landing. SIGMET warns aircraft in flight of specified significant en-route phenomena. Advisory centres provide specialist volcanic-ash and tropical-cyclone information.
Do not merge products
A warning is not a forecast chart, and an advisory is not automatically an ATC clearance. Use each in its operational context.
Aerodrome and light-aircraft warnings
Aerodrome warnings protect aircraft on the ground and airport operations from hazardous conditions. Fog, frost, thunderstorms, squalls, sand or dust storms and marked temperature inversions can all matter.
Hazard and location
Read phenomenon, intensity, affected location or runway, validity and expected change. A warning may be local to a runway or movement area, so its precise location affects the operational response.
Indian service detail
Joshi describes related light-aircraft and aerodrome warning support. Keep these service differences clearly labelled and do not call them Oxford SIGMET categories.
Windshear warnings
Windshear warnings address rapid changes in wind that can affect take-off and landing. Oxford places the main warning scope in the lower aerodrome environment, normally below 1600 ft above aerodrome level.
Read the message
A useful warning tells the crew the location or runway, the observed or expected shear, validity and change. Pilot reports are particularly valuable because they describe the aircraft effect.
Operational response
Compare the warning with wind, convective weather, terrain and approach path. The absence of a warning does not prove the absence of shear, especially near showers or terrain.
SIGMET structure
SIGMET is issued by a meteorological watch office for specified significant en-route weather affecting flight safety. Decode it in order: FIR or control area, issuer, validity, phenomenon, location, level, movement and expected intensity change.
Phenomena and extent
The message describes an actual or expected hazard and its area or coordinates. Vertical extent is essential. Thunderstorms, severe turbulence, severe icing, volcanic ash and tropical cyclones require different avoidance and update strategies.
Use the latest message
Plot movement and forecast change against the route time. A warning may remain valid while its most important sector moves away from the route or toward an alternate.
Volcanic ash and tropical cyclones
Volcanic ash advisory centres and tropical cyclone advisory centres provide specialist tracking and forecast support. Their products must be used with SIGMET, charts, reports and ATC information.
Volcanic ash
Ash can extend far from the volcano and change rapidly with wind at different levels. Avoidance planning requires the forecast ash area and vertical extent, not only the eruption location.
Tropical cyclone
TCAC and regional specialist centres provide forecast track and intensity information. Read the time, movement and expected development. Associated convection and wind extend beyond the plotted centre.
Apply warnings to the flight
Warnings matter only when turned into decisions. At departure, assess runway, windshear and terminal weather. En route, compare SIGMET with route and level. For diversion, reassess the alternate rather than carrying the original choice unchanged.
Cross-check products
Use SIGWX, satellite, radar, METAR, TAF and pilot reports to support the warning. Each product has a different time, height and coverage.
Indian service differences
Joshi's MWO, AIRMET and advisory service descriptions are supplementary Indian context. Name the product correctly and use the local AIP procedures for operational action.
Decode the warning field by field
- Issuer and FIR identify the meteorological watch office and affected flight information region.
- Validity gives the UTC start and end time.
- Phenomenon states the significant weather, such as severe turbulence, severe icing, embedded thunderstorms, volcanic ash or tropical cyclone.
- Location and level define the area and vertical extent.
- Movement and intensity show where the hazard is going and whether it is changing.
Aerodrome warnings can cover fog, frost, squalls, thunderstorms, sand or dust storms and marked temperature inversion. Windshear warnings should name the runway or approach/departure area and may be supported by a pilot report. VAAC products support ash avoidance; TCAC and RSMC products support cyclone tracking. Joshi's Indian MWO, AIRMET and GAMET material is supplementary service context, not an Oxford Ch28 category.
Phenomena and dissemination
SIGMET phenomena are limited to weather significant to aircraft operations. The message must be interpreted against the FIR boundary, not simply the departure or destination. A thunderstorm area may be isolated, occasional, frequent, embedded or obscured as coded. These descriptors affect whether visual avoidance is realistic.
For volcanic ash and tropical cyclones, the advisory centre provides specialist forecast support and the MWO issues the aviation warning for the FIR. The pilot's action remains based on the current warning, route geometry, forecast movement, fuel and ATC coordination. A warning's absence is not permission to fly through observed severe weather.
Aerodrome decision example
For a departure with fog and a windshear warning, separate ground visibility, runway RVR, reported cloud or vertical visibility and the shear location. If a SIGMET also affects the climb route, plot its level and movement. The decision may require a different runway, delayed departure, higher fuel for a return or diversion, or a route that avoids the warning area. Each action follows a different field in the message.
Message format and operational meaning
An aerodrome warning identifies the phenomenon, its intensity, location and validity. A windshear warning identifies the runway or flight path, the observed or expected effect and any change. A pilot report should be treated as a report at a time and height, not as a forecast for every arrival. A SIGMET adds the FIR, phenomenon, location, vertical limits, movement and forecast intensity. Those fields must remain separate when the crew plots the message.
For a thunderstorm SIGMET, note whether cells are embedded or obscured. Embedded cells cannot be reliably avoided visually and may require a large route change. For severe icing, compare the stated layer with the freezing level and the planned climb or descent profile. For severe turbulence, consider the level change available without entering a neighbouring hazard. For ash, avoid the forecast area rather than attempting visual penetration.
Centre responsibilities
The meteorological watch office issues SIGMET for its FIR. A volcanic ash advisory centre supplies specialist ash analysis and forecast products. A tropical cyclone advisory centre or regional specialised meteorological centre supplies cyclone track and intensity guidance. These services are linked, but their messages have different users and purposes. The crew receives the operational warning through the appropriate dissemination system and must maintain an updated route plot.
Joshi's material on local aerodrome, light-aircraft and windshear warnings adds Indian operational context. The DGCA student should identify the product by its published name, authority, validity and protected phase of flight rather than treating every warning as a SIGMET.
Warning sequence at diversion
When selecting an alternate, read the warning again for its valid period at the expected arrival time. A warning that clears before destination arrival can still affect the alternate or return aerodrome. Check the alternate TAF, latest METAR, route SIGWX and warning movement together. The weather decision should name the threatened phase of flight and the available escape option.
Validity check: a warning is actionable only inside its stated UTC period. If a forecast movement carries a hazard across the route after the current validity ends, obtain the replacement warning or advisory before relying on an earlier message.
Windshear information should be passed promptly to crews because its operational value decreases as the weather evolves. Record whether the report is observed or forecast and whether it applies to departure, approach or all runways.