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11.1 METARs, SPECI, TAFs & PIREPs
Airline Transport Pilot ATP
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1 Chapter 1: Advanced Aerodynamics & High-Speed Flight
1.1 Subsonic & Transonic Aerodynamics 1.2 Swept-Wing Aerodynamics & Stability 1.3 High-Altitude Mach Phenomena & High-Speed Buffet 1.4 Stall Aerodynamics & Transport Category Recovery
2 Chapter 2: Multi-Engine Aerodynamics & Performance
2.1 Asymmetric Thrust & Critical Engine Factors 2.2 Minimum Control Speeds 2.3 Multi-Engine Inoperative Flight & Drift Down
3 Chapter 3: Turbine Engine Principles & Systems
3.1 Gas Turbine Theory & Turbofan Architecture 3.2 Engine Control, FADEC & Fuel Delivery 3.3 Engine Starting, Operating Limits & Malfunctions 3.4 Thrust Reversers & Auxiliary Power Units
4 Chapter 4: Transport Category Aircraft Systems
4.1 Hydraulic & Pneumatic Power Distribution 4.2 Electrical Power Generation & Distribution 4.3 Pressurization, Environmental Control & Oxygen Systems 4.4 Ice & Rain Protection and Fire Detection/Extinguishing
5 Chapter 5: Flight Instruments, Air Data & Primary Flight Displays
5.1 Pitot-Static Systems & High-Altitude Errors 5.2 Gyroscopic, Inertial Navigation & Attitude Reference Systems 5.3 Electronic Flight Displays & Flight Director Systems
6 Chapter 6: Advanced Navigation, Avionics & Automation
6.1 Flight Management Systems (FMS) & VNAV/LNAV 6.2 Performance-Based Navigation (PBN) & RNP/RNAV 6.3 Autoflight, Autothrottle & Automation Management 6.4 Surveillance & Warning Systems
7 Chapter 7: Airman Certification & General Operating Regulations
7.1 Part 61 ATP Certification Requirements & Privileges 7.2 Medical Standards, Pilot Impairment & Reporting 7.3 Part 91 Operating & Equipment Rules for Transport Aircraft
8 Chapter 8: Part 117 Flight and Duty Limitations & Rest Requirements
8.1 Flight Duty Period (FDP) Limits & Rest Concepts 8.2 Augmented Flightcrews & Rest Facilities 8.3 Cumulative Duty/Flight Limits & Fatigue Risk Management
9 Chapter 9: Part 121 Domestic, Flag & Supplemental Operations
9.1 Part 121 Operational Structure & Dispatch Control 9.2 Domestic & Flag Fuel Requirements 9.3 Dispatch Minimums & Alternate Airport Selection 9.4 Takeoff Minimums, Takeoff Alternates & Part 121/135 Comparisons
10 Chapter 10: Aviation Meteorology & Atmospheric Hazards
10.1 Atmospheric Structure, Pressure Systems & Fronts 10.2 Convective Hazards, Thunderstorms & Microbursts 10.3 Structural & Induction Icing 10.4 Turbulence & Mountain Wave Dynamics
11 Chapter 11: Aviation Weather Reports, Forecasts & High-Altitude Charts
11.1 METARs, SPECI, TAFs & PIREPs 11.2 Significant Weather Charts (SIGWX) & Inflight Advisories 11.3 Constant Pressure Charts, Upper-Air Winds & Tropopause Analysis
12 Chapter 12: Transport Category Aircraft Performance & Flight Planning
12.1 Transport Category Takeoff Performance & V-Speeds 12.2 Climb Segments & Obstacle Clearance 12.3 Landing Performance, Contaminated Runways & Approach Speeds 12.4 Transport Category Weight & Balance
13 Chapter 13: High-Altitude Navigation, ETOPS, CRM & Safety
13.1 High-Altitude Operations, RVSM & Oceanic Procedures 13.2 Extended-Range Twin-Engine Operations (ETOPS / EDTO) 13.3 Crew Resource Management (CRM) & Threat and Error Management (TEM) 13.4 Aeromedical Factors & High-Altitude Physiology 13.5 Safety Management Systems (SMS) & NTSB 830 Accident Reporting
11.1 METARs, SPECI, TAFs & PIREPs
Key Takeaways Explain This Topic AI
METAR and SPECI reports encode surface weather and operational safety elements, including low-level wind shear below 2,000 ft AGL (WS020/24045KT), Runway Visual Range (e.g. R04R/2600FT, R22L/P6000FT, R16C/1000V2000FT), and standardized present weather descriptors.
Advanced METAR remarks contain critical flight planning data: sea level pressure in tenths of hPa (SLP142 = 1014.2 hPa, SLP982 = 998.2 hPa), high-precision temperature/dewpoint T-groups (T00441011 = +4.4°C / -1.1°C), peak winds (PK WND 28045/15), and variable ceilings (CIG 002V004).
Terminal Aerodrome Forecasts (TAFs) cover 24-hour or 30-hour periods; rapid permanent changes are forecast using FM groups (From), temporary fluctuations lasting <1 hour and covering <50% of the period use TEMPO groups, and domestic FAA TAFs use PROB30 (30% probability) rather than PROB40 or BECMG.
Pilot Weather Reports (PIREPs) are classified as Routine (UA) or Urgent (UUA); mandatory UUA criteria include severe or extreme turbulence, severe icing, hail, low-level wind shear (LLWS) with airspeed losses/gains of 10+ knots within 2,000 ft AGL, volcanic ash, and tornadoes/funnel clouds.
Icing intensities (Trace, Light, Moderate, Severe) and turbulence classifications (Light, Moderate, Severe, Extreme) require standardized cockpit reporting; severe icing or severe turbulence mandates immediate operational diversion.
Last updated: August 2026
METARs, SPECI, TAFs & PIREPs
Core Airline Transport Principle: Accurate tactical and strategic flight planning in air carrier operations depends on absolute fluency in decoding aviation weather reports, forecasts, and pilot reports. Under 14 CFR Part 121, operating decisions—ranging from takeoff alternate requirements and derived landing minimums to enroute diversions—hinge upon specific meteorological values encoded in METARs, TAFs, and PIREPs.
1. METAR & SPECI Syntax, Structure & Issuance Criteria
A METAR (Aviation Routine Weather Report) is the standard international surface observation code generated hourly between 45 and 55 minutes past each hour. A SPECI (Aviation Selected Special Weather Report) is an unscheduled report issued immediately whenever specific, operationally significant weather changes occur between routine hourly reports. +-----------------------------------------------------------------------------+
- | ANATOMY OF A TRANSPORT METAR / SPECI |
- | |
- | METAR KJFK 161851Z 32024G38KT 280V350 3/4SM R04R/2600FT +TSRAGS FG |
- | BKN008 OVC015CB 18/16 A2982 WS020/28055KT RMK AO2 PK WND 31048/42 |
- | SLP098 T01780161 56012 P0018 $ |
- | |
- | [KJFK] Station Identifier (ICAO 4-letter code) |
- | [161851Z] Date/Time: 16th day of month at 1851 UTC (Zulu) |
- | [32024G38KT] Wind: 320° True at 24 kts, Gusting to 38 kts |
- | [280V350] Variable Wind Direction: Between 280° and 350° (speed >= 6 kts)|
- | [3/4SM] Prevailing Visibility: 3/4 Statute Mile |
- | [R04R/2600FT] Runway Visual Range: Runway 04 Right is 2,600 feet |
- | [+TSRAGS FG] Present Weather: Heavy Thunderstorm, Rain, Small Hail/Pellets, Fog|
- | [BKN008 OVC015CB] Sky Condition: Broken 800 ft, Overcast 1,500 ft CB |
- | [18/16] Temperature/Dewpoint: +18°C / +16°C |
- | [A2982] Altimeter Setting: 29.82 inHg |
- | [WS020/28055KT] Wind Shear: At 2,000 ft AGL, Wind 280° at 55 knots |
- | [RMK ...] Remarks Section: Detailed sensor, pressure, and thermal data |
- +-----------------------------------------------------------------------------+
- Mandatory SPECI Issuance Thresholds
Automated observing systems (ASOS/AWOS) and human observers must immediately transmit a SPECI when any of the following operational parameters are breached:
Ceiling Changes: A ceiling forms, disappears, or crosses above or below critical approach minimum thresholds: 3,000 ft, 1,500 ft, 1,000 ft, 500 ft, 200 ft (CAT I decision height), or the lowest published airport IFR landing minimum.
Visibility Changes: Prevailing visibility decreases or increases across key regulatory milestones: 3 SM, 2 SM, 1 SM, 3/4 SM, 1/2 SM, or the lowest published landing minimum.
Wind Shift: Wind direction changes by 45 ∘ 45^\circ 4 5 ∘ or more in less than 15 minutes, with sustained wind speeds of at least 10 knots.
Hazardous Present Weather: Inception, cessation, or change in intensity of:
Tornado, funnel cloud, or waterspout.
Thunderstorm ( T S TS TS ).
Freezing precipitation (freezing rain − F Z R A / F Z R A -FZRA/FZRA − FZR A / FZR A , freezing drizzle F Z D Z FZDZ FZ D Z ).
Ice pellets ( P L PL P L ) or hail ( G R / G S GR/GS GR / GS ).
Squall ( S Q SQ SQ ).
Runway Visual Range (RVR): RVR decreases below or increases above 2,400 feet (1/2 SM equivalent) on any active instrument runway within a 10-minute period.
- 2. Low-Level Wind Shear & Runway Visual Range (RVR) Encoding
- Low-Level Wind Shear in the Body
When non-convective low-level wind shear is detected by terminal sensors (such as Low-Level Wind Shear Alert System [LLWAS] or Terminal Doppler Weather Radar [TDWR]) along the runway approach or departure corridor up to 2,000 feet AGL, it is encoded in the main body: WS [ Altitude in hundreds of ft AGL ] / [ Wind Direction ] [ Speed ] KT \text{WS}[\text{Altitude in hundreds of ft AGL}]/[\text{Wind Direction}][\text{Speed}]\text{KT} WS [ Altitude in hundreds of ft AGL ] / [ Wind Direction ] [ Speed ] KT
Example: WS020/24045KT indicates wind shear at 2,000 feet AGL with a wind vector of 240 ∘ 240^\circ 24 0 ∘ True at 45 knots.
Example: WS010/18050KT indicates wind shear at 1,000 feet AGL with a wind vector of 180 ∘ 180^\circ 18 0 ∘ True at 50 knots. +-----------------------------------------------------------------------------+
- | RUNWAY VISUAL RANGE (RVR) SYNTAX MATRIX |
- | |
- | Encoded Format Operational Translation |
- | ----------------------------------------------------------------------- |
- | R04R/2600FT Runway 04 Right RVR is constant 2,600 feet. |
- | R22L/P6000FT Runway 22 Left RVR exceeds 6,000 feet (P = Plus). |
- | R16C/M0600FT Runway 16 Center RVR is below 600 feet (M = Minus).|
- | R28/1000V2000FT Runway 28 RVR is variable between 1,000 & 2,000 ft.|
- | R01L/1200V2400V0800FT Variable RVR across touchdown, mid, and rollout. |
- | R09/2200U ICAO: Runway 09 RVR 2,200 meters, upward trend (U).|
- | R27/1400D ICAO: Runway 27 RVR 1,400 meters, downward trend (D)|
- | R33/1800N ICAO: Runway 33 RVR 1,800 meters, no change (N). |
- +-----------------------------------------------------------------------------+
RVR Measurement Systems: Transmissometers or forward-scatter meters measure visual range at Touchdown (TDZ), Mid-Point (MID), and Rollout (RO). In US operations, values are reported in hundreds of feet; internationally, values are in meters with trend indicators ( U U U = upward, D D D = downward, N N N = no change).
3. Present Weather Qualifiers, Descriptors & Obscurations
Present weather is constructed using a systematic combination of Intensity/Proximity , Descriptor , and Phenomena codes. +-----------------------------------------------------------------------------+
- | PRESENT WEATHER CODE CONSTRUCTION |
- | |
- | [Intensity / Proximity] + [Descriptor] + [Precipitation / Obscuration] |
- | |
- | Examples: |
- | - -FZDZ = Light Freezing Drizzle |
- | - +TSRASN = Heavy Thunderstorm with Rain and Snow |
- | - VCBCHZ = Patches of Haze in the Vicinity (5 to 10 SM from airport) |
- | - +BLSN = Heavy Blowing Snow (lifted >= 2 meters / 6 feet above ground)|
- | - MIFG = Shallow Fog (depth < 2 meters / 6 feet above ground) |
- | - PRFG = Partial Fog (covers part of the aerodrome) |
- | - BCFG = Patches of Fog (random fog patches across aerodrome) |
- | - FZFG = Freezing Fog (supercooled water droplets at temp <= 0°C) |
- +-----------------------------------------------------------------------------+
- Comprehensive Present Weather Matrix
Category Code Meaning Operational Notes
Intensity / Proximity - Light Minimal rate of accumulation or reduction in visibility.
(none) Moderate Standard precipitation rate.
+ Heavy Significant accumulation, severe reduction in visibility.
VC Vicinity Weather phenomenon observed between 5 and 10 SM from station.
Descriptors MI Shallow Less than 2 meters (6 feet) deep.
PR Partial Substantial part of aerodrome covered.
BC Patches Irregular patches over aerodrome.
DR Low Drifting Lifted by wind less than 2 meters above ground.
BL Blowing Lifted by wind 2 meters or more above ground.
SH Showers Convective precipitation with rapid starts and stops.
TS Thunderstorm Lightning / thunder detected within past 15 minutes.
FZ Freezing Supercooled liquid droplets freezing on impact.
Precipitation DZ Drizzle Very small droplets (diameter < 0.5 mm), slow fall speed.
RA Rain Droplets diameter ≥ 0.5 mm \ge 0.5\text{ mm} ≥ 0.5 mm .
SN Snow Hexagonal ice crystals, aggregates, or flakes.
SG Snow Grains Very small, white, opaque grains of ice (equivalent of drizzle).
IC Ice Crystals Diamond dust, unbranched ice crystals floating in cold air.
PL Ice Pellets Frozen raindrops (sleet); indicates freezing rain aloft.
GR Hail Hailstones diameter ≥ 5 mm \ge 5\text{ mm} ≥ 5 mm (1/4 inch).
GS Small Hail / Snow Pellets Diameter < 5 mm < 5\text{ mm} < 5 mm (graupel).
UP Unknown Precip Automated sensor detected precipitation of undetermined type.
Obscurations FG Fog Visibility < 5 / 8 SM < 5/8\text{ SM} < 5/8 SM ( < 1 , 000 m < 1,000\text{ m} < 1 , 000 m ), RH ≈ 100 % \approx 100\% ≈ 100% .
BR Mist Visibility 5 / 8 SM 5/8\text{ SM} 5/8 SM to 6 SM 6\text{ SM} 6 SM , RH ≥ 80 % \ge 80\% ≥ 80% .
FU Smoke Suspended combustion particles.
VA Volcanic Ash Extremely abrasive pulverized rock; flight hazard.
DU Widespread Dust Finely divided earth particles in suspension.
SA Sand Sand particles suspended in the atmosphere.
HZ Haze Dry particulate suspension, RH < 80 % < 80\% < 80% .
PY Spray Water droplets torn from wave crests by gale-force winds.
Other SQ Squall Wind increase ≥ 16 kts \ge 16\text{ kts} ≥ 16 kts , sustained ≥ 22 kts \ge 22\text{ kts} ≥ 22 kts for ≥ 1 min \ge 1\text{ min} ≥ 1 min .
FC Funnel Cloud Tornado or waterspout ( +FC = tornado/waterspout touching surface).
SS / DS Sandstorm / Duststorm Visibility < 5 / 16 SM < 5/16\text{ SM} < 5/16 SM in blowing sand or dust.
PO Dust/Sand Whirls Well-developed dust devils.
4. Advanced Remarks (RMK) Decoding
The remarks section contains precision meteorological data critical for transport category operations, altimetry, density altitude, and frontal tracking. +-----------------------------------------------------------------------------+
- | PRECISION REMARKS DECODING GUIDE |
- | |
- | Remark Code Decoded Operational Information |
- | ----------------------------------------------------------------------- |
- | AO1 / AO2 Station type: AO1 = without precip discriminator; |
- | AO2 = with liquid/frozen precip discriminator. |
- | |
- | PK WND 28045/15 Peak Wind: 280° at 45 kts occurred at 15 past hour. |
- | |
- | WND DATA EST Wind data estimated due to sensor malfunction. |
- | |
- | CIG 002V004 Ceiling variable between 200 ft and 400 ft AGL. |
- | |
- | CIG 005 RWY16 Ceiling 500 ft AGL specifically over Runway 16 sensor.|
- | |
- | SLP142 Sea Level Pressure: 1014.2 hPa (14.2 -> 1014.2). |
- | SLP982 Sea Level Pressure: 998.2 hPa (98.2 -> 998.2). |
- | * Rule: If 1st digit is 0-5, prefix with 10 (1000s). |
- | * Rule: If 1st digit is 6-9, prefix with 9 (900s). |
- | |
- | T00441011 Precision Temp/Dewpoint: +4.4°C / -1.1°C. |
- | * Format: T[sn][TTT][sn][TTT] |
- | * sn = 0 (Positive) or 1 (Negative / Subzero). |
- | * T0044 -> +4.4°C; T1011 -> -1.1°C. |
- | * T10281056 -> Temp -2.8°C, Dewpoint -5.6°C. |
- | |
- | 56012 3-Hour Pressure Tendency: Code 5 (decrease then steady|
- | or decrease), fell 1.2 hPa in past 3 hours. |
- | |
- | P0018 Hourly Precipitation Accumulation: 0.18 inches. |
- | 60045 3- or 6-Hour Precipitation Accumulation: 0.45 inches. |
- | 70120 24-Hour Precipitation Accumulation: 1.20 inches. |
- | |
- | PRESRR / PRESFR Pressure Rising Rapidly / Pressure Falling Rapidly |
- | (>= 0.06 inHg or 2.0 hPa per hour). |
- | |
- | FROPA Frontal Passage occurred during observation interval. |
- | VIRGA Precipitation aloft evaporating before reaching ground|
- | CB DSNT NW MOV E Cumulonimbus distant northwest, moving east. |
- | $ Maintenance indicator (sensor requires servicing). |
- +-----------------------------------------------------------------------------+
- 5. Terminal Aerodrome Forecasts (TAF): Architecture & Rules
A TAF is a concise statement of expected meteorological conditions at an airport within a 5-statute-mile radius of the center of the runway complex. TAFs are issued 4 times daily (0000Z, 0600Z, 1200Z, 1800Z) by National Weather Service Weather Forecast Offices (WFOs). +-----------------------------------------------------------------------------+
- | TAF ANATOMY & STRUCTURE |
- | |
- | TAF KORD 161730Z 1618/1724 20015G25KT 5SM HZ BKN030 |
- | WS020/22045KT |
- | FM162200 24018KT 3SM +TSRA BKN015CB OVC030 |
- | TEMPO 1623/1702 1/2SM +TSRAGS FG BKN005 OVC010CB |
- | FM170300 32014KT P6SM SKC |
- | PROB30 1708/1712 2SM BR BKN010 |
- | |
- | - Validity Period: 1618/1724 = Valid from 16th at 1800Z to 17th at 2400Z |
- | (30-hour validity window for high-density international hub). |
- | - Base Forecast: 200° at 15G25KT, 5 SM Haze, Broken 3,000 ft, |
- | Low-level wind shear at 2,000 ft AGL from 220° at 45 kts. |
- +-----------------------------------------------------------------------------+
- Validity Periods: 24-Hour vs. 30-Hour TAFs
24-Hour TAFs: Standard for regional, domestic, and non-hub aerodromes.
30-Hour TAFs: Issued for designated major international gateways (e.g., KORD, KJFK, KLAX, KDFW, KATL) to support long-haul international flight dispatch under 14 CFR Part 121 Flag and Supplemental operations.
Change Group Rules & Definitions +-----------------------------------------------------------------------------+
- | TAF CHANGE GROUPS COMPARISON |
- | |
- | Group Code Duration & Probability Operational Rules |
- | ----------------------------------------------------------------------- |
- | FMddhhmm Permanent, rapid change - Full weather transition in |
- | (From) occurring in < 1 hour. less than 60 minutes. |
- | - Completely overwrites all |
- | previous forecast lines. |
- | - Requires 2-digit minute time|
- | (e.g., FM162200). |
- | |
- | TEMPO Temporary fluctuations - Each instance lasts < 1 hr. |
- | ddhh/ddhh expected for < 50% of the - Total duration < 50% of the |
- | specified time window. prescribed TEMPO window. |
- | - Only modified elements are |
- | listed; unmentioned elements|
- | revert to prevailing base. |
- | |
- | PROB30 30% Probability of - Represents 30% to 39% chance|
- | ddhh/ddhh hazard or precipitation. of convective/IFR conditions|
- | - Prohibited in first 9 hrs |
- | of domestic US TAFs. |
- | - Under standard Part 121, |
- | PROB30 conditions alone do |
- | not disqualify dispatch if |
- | main body is above minimums.|
- | |
- | PROB40 / BECMG International / Military - PROB40 and BECMG are NOT |
- | (Becoming) codes. used in domestic FAA TAFs. |
- | - Used extensively in ICAO |
- | TAFs across Europe and Asia.|
- +-----------------------------------------------------------------------------+
Important
FAA Domestic TAF Policy on PROB40 and BECMG: In domestic United States NWS TAFs, the PROB40 group is never used; if the probability of a phenomenon reaches 40% or greater, it must be forecast as a prevailing condition or within a TEMPO or FM group. Furthermore, BECMG (Becoming) is not authorized in standard domestic FAA TAFs (except for military aerodromes), ensuring unambiguous, discrete transition times for commercial air carrier dispatch.
6. Pilot Weather Reports (PIREP): Routine (UA) vs. Urgent (UUA)
Pilot reports provide ground meteorologists, dispatchers, and following flight crews with real-time verification of atmospheric conditions aloft. PIREPs are transmitted in standard coded format: +-----------------------------------------------------------------------------+
- | PIREP CODING ELEMENTS MATRIX |
- | |
- | Field Code Element Name Example Encoding |
- | ----------------------------------------------------------------------- |
- | /OV Location /OV JFK 120025 (JFK VOR 120° at 25NM)|
- | /TM Time (UTC) /TM 1942 |
- | /FL Flight Level / Altitude /FL330 (or /FL020 for 2,000 ft MSL) |
- | /TP Type Aircraft /TP B77W (Boeing 777-300ER) |
- | /SK Sky Cover /SK OVC012-TOP085 / BKN180-TOP240 |
- | /WX Weather / Visibility /WX FV02SM +RA FG |
- | /TA Air Temperature (°C) /TA -48 |
- | /WV Wind Velocity /WV 270110KT |
- | /TB Turbulence /TB SEV CAT FL310-350 |
- | /IC Icing /IC SEV CLR 040-080 |
- | /RM Remarks /RM LLWS +/- 18KT ON FINAL RWY 04R |
- +-----------------------------------------------------------------------------+
- Mandatory Urgent PIREP ( UUA ) Reporting Triggers
A PIREP must be classified and immediately broadcast as Urgent (UUA) when any of the following extreme atmospheric hazards are reported:
Severe or Extreme Turbulence (including Clear Air Turbulence [CAT]).
Severe Icing (ice accumulation rate exceeds deicing/anti-icing capability; immediate diversion required).
Hail of any size (or ≥ 3 / 4 \ge 3/4 ≥ 3/4 inch in diameter).
Volcanic Ash Clouds (airframe abrasion, engine flameout hazard).
Low-Level Wind Shear (LLWS) with airspeed fluctuations of 10 knots or greater within 2,000 feet AGL.
Tornadoes, Funnel Clouds, or Waterspouts .
Any other weather phenomenon deemed by the PIC or ATC to present an immediate hazard to flight safety . +-----------------------------------------------------------------------------+
- | TURBULENCE & ICING CLASSIFICATION MATRIX |
- | |
- | Classification Operational Definition & Airframe Impact |
- | ----------------------------------------------------------------------- |
- | [TURBULENCE] |
- | Light Slight erratic changes in altitude/attitude. Unsecured |
- | objects displace slightly. Walking effortless. |
- | Moderate Rapid bumps/jolts. Definite strain against seatbelts. |
- | Unsecured objects dislodged. Walking difficult. |
- | Severe Large, abrupt changes in altitude/attitude. Aircraft |
- | temporarily out of control. Occupants forced violent- |
- | ly against seatbelts. Unsecured objects tossed about. |
- | Extreme Aircraft violently tossed, practically impossible to |
- | control. Structural damage possible. Immediate declare.|
- | Chop vs. Turb Chop = rapid, rhythmic bumpiness without altitude/ |
- | attitude variations. Turb = erratic structural motion. |
- | |
- | [ICING] |
- | Trace Ice becomes perceptible; rate of accumulation slightly |
- | greater than rate of sublimation. No hazard. |
- | Light Accumulation rate may create hazard if flight prolonged|
- | (> 1 hour). Occasional deicing equipment cycles needed.|
- | Moderate Accumulation rate requires continuous/frequent deicing.|
- | Potentially hazardous; diversion necessary if failed. |
- | Severe Accumulation exceeds capability of anti-ice/deicing |
- | equipment. Ice builds on unprotected surfaces. |
- | MANDATORY IMMEDIATE EMERGENCY DIVERSION. |
- +-----------------------------------------------------------------------------+