Study guide
4.4 In-Flight Advisories: AIRMETs, SIGMETs & Convective SIGMETs
FAA Aircraft Dispatcher Certificate ADX
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1 Chapter 1: Regulations, Certification & Operational Control
1.1 Part 65 Subpart C: Certification, Eligibility & Currency 1.2 Operational Control & Dispatcher-PIC Joint Responsibility 1.3 Domestic, Flag & Supplemental Operations Framework 1.4 Dispatch Release Elements, Signatures & Recordkeeping 1.5 Regulations, Manuals, Crew Qualifications, and Source Control
2 Chapter 2: Atmospheric Physics, Pressure Systems & Fronts
2.1 Atmospheric Structure, Standard Atmosphere & Altimetry 2.2 Air Masses, Frontal Systems & Frontogenesis 2.3 Atmospheric Stability, Lapse Rates & Cloud Formation 2.4 Earth Motion, Regional Weather, Local Winds, and Water Phase Changes
3 Chapter 3: Aviation Weather Hazards & Severe Weather Avoidance
3.1 Structural and Induction Icing: Types, Accretion & Operations 3.2 Thunderstorms, Squall Lines, Microbursts & Low-Level Windshear 3.3 Clear Air Turbulence (CAT), Mountain Waves & Jet Streams 3.4 Low Ceilings, Fog Types & Visibility Restrictions 3.5 Hurricanes, Typhoons, Tornadoes, and Tropical Dispatch Hazards
4 Chapter 4: Weather Observations, Forecasts & Advisories Decoding
4.1 METAR and SPECI Surface Observations: Decoding & Operations 4.2 Terminal Aerodrome Forecasts (TAF): Groups & Timing 4.3 Pilot Weather Reports (PIREP): Coding, Severity & Urgent Alerts 4.4 In-Flight Advisories: AIRMETs, SIGMETs & Convective SIGMETs 4.5 Weather Collection, NWS Facilities, GFA, and EWINS
5 Chapter 5: Aviation Weather Charts & Upper-Air Analysis
5.1 Surface Analysis & Radar Summary Charts 5.2 Constant Pressure Analysis & Winds Aloft (FB) 5.3 Significant Weather Prognostic Charts (SIGWX) 5.4 Satellite Imagery, Moisture-Stability Analysis, and Forecast Integration
6 Chapter 6: Air Navigation, Airspace Architecture & Route Structure
6.1 National Airspace System: Classes, Rules & Special Use 6.2 Ground-Based Navigation Aids & Standard Service Volumes 6.3 Area Navigation (RNAV), GNSS/GPS, PBN & RNP Fundamentals 6.4 En Route Airways, SIDs, STARs & Chart Interpretation 6.5 Earth Coordinates, UTC, Chart Projections, and Flight Instruments 6.6 North Atlantic, Pacific, RVSM, and Global Navigation Differences
7 Chapter 7: Instrument Approaches, Minimums & Airport Operations
7.1 Precision Approach Systems: ILS Categories & Tolerances 7.2 Non-Precision Approaches, RNAV & Decision Minimums (MDA/DA) 7.3 Takeoff Minimums, Lower-Than-Standard & Takeoff Alternates 7.4 Holding Procedures: Patterns, Speed Limits & Timing
8 Chapter 8: Subsonic Aerodynamics & Jet Aircraft Performance
8.1 Subsonic Jet Aerodynamics: Lift, Drag & Flight Regimes 8.2 High-Altitude Flight: Mach Number, Buffet & Coffin Corner 8.3 Transport Turbine Engines: Thrust, Specific Fuel & Bleed Air
9 Chapter 9: Transport Category Takeoff & Landing Runway Analysis
9.1 Takeoff Performance Speeds & Balanced Field Concept 9.2 Takeoff Climb Segments & Obstacle Clearance Gradients 9.3 Landing Performance: Field Lengths, 60% Rule & Contamination
10 Chapter 10: En Route Performance, Driftdown Profiles & ETOPS Operations
10.1 One/Two-Engine-Inoperative En Route Net Profiles & Driftdown 10.2 Extended-Range Operations (ETOPS): Philosophy & Regulations 10.3 ETOPS En Route Alternates: Adequate vs. Suitable & Critical Fuel
11 Chapter 11: Aircraft Weight & Balance, Center of Gravity, and Loading
11.1 Transport Aircraft Structural Weight Limits: Definitions & Rules 11.2 Center of Gravity Computations: Datum, Arm, Moment & Index 11.3 Mean Aerodynamic Chord (%MAC) Computations & Stability 11.4 Payload-Range Analysis, Zero Fuel Weight Tradeoffs & Loading
12 Chapter 12: Destination Alternate Airport Selection & Weather Rules
12.1 Destination Alternate Selection: 91.169 & Part 121 1-2-3 Rule 12.2 Flag & Supplemental Operations Destination Alternate Rules 12.3 Derived Alternate Minimums: 1-Nav and 2-Nav Facility Rules
13 Chapter 13: Part 121 Fuel Planning, Reserves & En Route Re-Release
13.1 Part 121 Domestic Fuel Requirements: Reserves & Calculations 13.2 Part 121 Flag Fuel Requirements: 10% Reserve & Island Rules 13.3 Supplemental Fuel Requirements & Holding Fuel Management 13.4 Redispatch and En Route Re-release Procedures
14 Chapter 14: Transport Systems, Pressurization & MEL/CDL Procedures
14.1 Transport Jet Auxiliary Power, Electrical, Hydraulic & Pneumatic Systems 14.2 Cabin Pressurization, Rapid Decompression & Oxygen Requirements 14.3 Master Minimum Equipment List (MMEL), MEL & CDL Procedures 14.4 Flight Controls, Autoflight, Fuel, Oil, Brakes, and Fire Protection
15 Chapter 15: Hazardous Materials, Duty Regulations & Emergency Procedures
15.1 Dangerous Goods Carriage by Air (49 CFR Part 175) & NOTOC 15.2 Dispatcher Duty Limitations, Rest Requirements & Fatigue 15.3 Emergency Authority, Declaration & Diversion Decision-Making 15.4 NTSB Part 830 Accident Reporting & Wreckage Preservation 15.5 Security, Overdue Aircraft, and FAA Emergency Services
16 Chapter 16: Communications, ATC, and Flight Plan Procedures
16.1 Voice, Data Link, Position Reports, and Lost Communications 16.2 ATC Facilities, Separation, ICAO Flight Plans, and Traffic Management
17 Chapter 17: Human Factors and Practical Dispatch Applications
17.1 Dispatch Resource Management, Human Error, and Risk Decisions 17.2 Manual Flight Planning, PIC Briefing, Flight Watch, and Postflight Closeout
4.4 In-Flight Advisories: AIRMETs, SIGMETs & Convective SIGMETs
Key Takeaways Explain This Topic AI
CONUS text AIRMETs retired January 27, 2025; G-AIRMET forecast snapshots must be interpreted across time.
CONUS non-convective SIGMETs are unscheduled and valid up to four hours.
Convective SIGMET bulletins are issued hourly at H+55 and valid two hours or until superseded.
A CWA is a short-term center advisory; an MIS supports longer-range planning.
§ 121.629(a), aircraft limitations, and actual conditions govern unsafe-icing decisions; § 121.341 has a different equipment and applicability scope.
Last updated: October 2026
Inflight Advisories: Products, Timing, and Dispatch Decisions
An inflight weather advisory identifies hazardous weather affecting a region, altitude layer, and period. Its polygon is a useful overview, but the text, movement, vertical limits, and validity times matter. Dispatchers compare the advisory with the proposed route and each active flight, then combine observations, forecasts, imagery, and PIREPs. Neither absence of an advisory nor location just outside its drawn boundary proves that conditions are safe.
Current AIRMET formats
Traditional alphanumeric CONUS text AIRMETs were retired January 27, 2025 . Current contiguous-U.S. planning uses G-AIRMETs . These present hazards at discrete forecast times, ordinarily no more than three hours apart, out to twelve hours. A snapshot is not a promise that a hazard exists only at that instant: evaluate changes between snapshots and defined onset/end times. Text AIRMETs remain applicable in Alaska and Hawaii under their regional formats and issuance rules.
The familiar hazard families remain useful:
- Family Principal hazards
- Sierra IFR ceilings/visibility and extensive mountain obscuration
- Tango Moderate turbulence, strong sustained surface winds, non-convective low-level wind shear
- Zulu Moderate icing and freezing-level information
The 2026 Aviation Weather Handbook identifies CONUS IFR advisory thresholds as ceilings below 1,000 feet and/or visibility below 3 SM. Non-convective LLWS concerns the layer below 2,000 feet AGL. The handbook's CONUS strong-surface-wind criterion is greater than 30 knots; regional text descriptions should be read in their own scope. Do not present every AIRMET everywhere as a six-hour text bulletin. AIRMET-level weather is relevant to transport airplanes, especially during diversion, descent, approach, and ground operations.
CONUS non-convective SIGMETs
A SIGMET addresses significant hazards to aircraft, not just light aircraft. In the CONUS, non-convective criteria include severe or greater turbulence, severe icing, widespread dust or sand storms, and volcanic ash. These are unscheduled products with validity up to four hours . A continuing phenomenon is reissued as necessary. Read the top and bottom altitudes, movement, and expected continuation beyond the current bulletin.
International SIGMETs and tropical-cyclone/volcanic-ash products outside the CONUS have their own formats and validity provisions, including some periods up to six hours. Applying that six-hour value to every CONUS ash bulletin is incorrect. Identify the issuing meteorological watch office and flight information region before importing a domestic mnemonic into an oceanic briefing.
Convective SIGMETs
CONUS Convective SIGMET bulletins are issued hourly at 55 minutes past the hour for eastern, central, and western regions. They are valid for two hours or until superseded. A “NONE” bulletin is issued if the criteria are not met. Any Convective SIGMET implies severe or greater turbulence, severe icing, and LLWS associated with the convection.
Routine criteria include a line of thunderstorms at least 60 miles long with thunderstorms affecting at least 40 percent of its length; an area of active thunderstorms with significant impact, at least 40 percent coverage and a strong radar/satellite/lightning signature; and embedded or severe thunderstorms expected for more than 30 minutes. Special criteria include tornadoes, surface hail at least 3/4 inch , or surface wind gusts at least 50 knots , with the time and forecaster-judgment provisions described in the handbook. Do not invent a universal 3,000-square-mile requirement for every current Convective SIGMET.
That 3/4-inch aviation advisory criterion is distinct from the National Weather Service's general severe-thunderstorm warning hail criterion and from urgent PIREP categorization, where reported hail is urgent without that size cutoff. Questions mixing these products require attention to the actual product named.
Center Weather Advisories and planning outlooks
A Center Weather Advisory (CWA) is a short-term, unscheduled advisory from a Center Weather Service Unit supporting its ARTCC. It can address conditions meeting or approaching national advisory criteria, conditions not adequately covered by another product, or hazards needing a prompt local update. Its validity is up to two hours. A Meteorological Impact Statement (MIS) supports longer planning, with validity up to 48 hours; it is not a tactical penetration clearance.
During flight watch, a CWA can reveal developing weather before a broader bulletin is updated. Brief the crew promptly, assess the affected altitude and time, and check whether a reroute, delay, or diversion is needed. A new CWA does not automatically cancel every release in the center, and a dispatcher's duty does not depend on waiting for a particular product to be issued.
Icing and the correct legal rule
Section 121.629(a) prohibits dispatch, release, continued enroute operation, or landing when, in the applicable PIC/dispatcher opinion, icing expected or encountered might adversely affect safety. Section 121.341 supplies icing-equipment requirements and particular restrictions for the non-transport airplanes described in paragraph (c). It is not a universal wording that bans every transport-category flight inside every forecast severe-icing polygon.
A severe-icing SIGMET along the planned altitude is a serious planning issue. Verify the aircraft's certified envelope, AFM limitations, actual weather information, and carrier procedures. If the plan exposes the flight to unsafe icing, change altitude or route, delay, or cancel. A generic belief that thermal anti-ice makes any forecast harmless is equally incorrect. The required decision connects the hazard to the airplane and proposed operation.
Worked flight-watch exercise
A hypothetical flight is planned at FL320. A SIGMET describes severe icing between FL280 and FL360 across a segment it will reach at 0210Z. The dispatcher first checks the bulletin's validity and movement, then compares current imagery and PIREPs with the route. A southern reroute adds 20 minutes; a lower route introduces terrain and additional fuel considerations. Evaluate both options using approved performance and fuel data, brief the PIC, and record the chosen amendment. Send timely safety information under § 121.601 rather than merely archiving the bulletin.
For thunderstorms, FAA guidance recommends at least 20 NM avoidance for severe or intense cells, with additional care downwind and around anvils. This is weather-avoidance guidance, not a universal legal dBZ/flight-level formula. Current radar polygons move and data links have latency. Plan a viable strategic corridor while the crew uses appropriate real-time information and ATC clearance for tactical deviations.
Official References
Source check: 2026-10-12 . 2026 FAA Aviation Weather Handbook ; Current NWS TAF policy (October 2024) ; AWC current products ; Dispatcher weather information § 121.601 . For operational use, apply current issued authorizations and the assigned aircraft’s approved data.