What is the difference between CIP and FIP icing products?

The Current Icing Product (CIP) is a real-time, hourly-updated three-dimensional analysis of current icing conditions, fusing radar, satellite, pireps, and model data. The Forecast Icing Product (FIP) uses the same output fields but is derived solely from numerical weather prediction models, providing icing forecasts out to 12 hours in hourly increments. Dispatchers use CIP to assess conditions at departure and CIP/FIP together to anticipate icing along the planned route.

Can an aircraft certified for flight into known icing legally fly through supercooled large droplet (SLD) conditions?

Not necessarily. Standard FAA FIKI certification under 14 CFR Part 25, Appendix C, does not include SLD environments such as freezing drizzle or freezing rain. An aircraft must have a separate SLD certification evaluated under Appendix O of Part 25 to be approved for those conditions. Dispatchers must verify SLD-specific approval before releasing a flight into forecast SLD icing.

How do dispatchers use icing forecasts when making a flight release decision?

Dispatchers layer CIP, FIP, AIRMETs, SIGMETs, and pireps to build a three-dimensional picture of icing along the proposed route and compare that picture against the aircraft's certification (FIKI and SLD approval), MEL status of ice protection equipment, available alternate altitudes or routes, and fuel reserves needed for anti-ice system operation. If forecast icing exceeds the aircraft's certification or equipment capability—especially severe icing or SLD without Appendix O approval—the dispatcher must reroute, select an alternate altitude, or decline to release the flight.

Icing Forecasts, FIP and CIP Products, and Anti-Ice Dispatch Considerations

Icing is one of the most insidious hazards in aviation. Unlike turbulence or thunderstorms, structural ice can accumulate silently and rapidly, degrading lift, increasing drag and weight, and degrading control authority—sometimes before the flight crew realizes a serious threat exists. For the aircraft dispatcher, icing is not just a weather awareness issue; it is a legal and operational one. Dispatchers share authority and responsibility for the safety of each flight under 14 CFR Part 121, which means they must understand what icing forecast products are saying and how to apply that information to release decisions.

Modern icing forecasting relies on two complementary gridded products—the Current Icing Product (CIP) and the Forecast Icing Product (FIP)—issued by the Aviation Weather Center (AWC). Together these products replace older, more qualitative pirep-only methods with three-dimensional, probability-based guidance that dispatchers can cross-check against aircraft certification, route altitude, and time of arrival. This article explains how CIP and FIP work, what their outputs mean operationally, and how dispatchers apply anti-icing considerations to flight release decisions.

How Structural Icing Forms

Before examining forecast products, a dispatcher must understand what drives icing. Structural icing occurs when an aircraft flies through visible moisture—cloud droplets, freezing rain, or freezing drizzle—at temperatures at or below 0°C (32°F). The FAA Aviation Weather Handbook (FAA-H-8083-28B) identifies three main types of structural ice: rime ice, which forms when small, supercooled droplets freeze almost instantly on contact and create a rough, opaque, relatively light accretion; clear (glaze) ice, which results from large droplets or freezing rain that spread before freezing, producing a dense, transparent, highly aerodynamically disruptive layer; and mixed ice, a combination of both. Clear ice is generally the most hazardous because it is harder to detect, heavier, and adheres more strongly to airframe surfaces.

The severity of icing is described as trace, light, moderate, or severe. At severe intensity, ice accumulates faster than anti-icing or de-icing equipment can handle it, and immediate exit from the conditions is required. FAA-H-8083-28B also emphasizes Supercooled Large Droplets (SLD)—freezing drizzle (FZDZ) and freezing rain (FZRA)—as a particularly dangerous sub-category because these larger drops can impinge on areas of the airframe that are not protected by standard ice protection systems, such as the aft portion of a wing or horizontal stabilizer. Freezing drizzle is generally associated with droplet diameters greater than 50 microns, while freezing rain droplets are typically larger still, often exceeding 100 microns and ranging up to several hundred microns.

Current Icing Product (CIP) and Forecast Icing Product (FIP)

The AWC's Current Icing Product (CIP) is a real-time, three-dimensional analysis of the icing environment. It fuses multiple data streams: METAR surface observations, radiosonde balloon data, satellite imagery, radar reflectivity, and pireps. The algorithm converts these inputs into a gridded field updated hourly at multiple flight levels from the surface up to approximately FL390. CIP outputs include:

Icing probability — expressed as a percentage (0–100%) that icing conditions exist at a given altitude and location at the analysis time.
Icing severity — a categorical estimate (trace through severe) where probabilities exceed a threshold.
SLD potential — a separate probability field specifically flagging the likelihood of supercooled large droplet conditions.

The Forecast Icing Product (FIP) uses the same output fields but is derived from the Rapid Refresh (RAP) numerical weather prediction model rather than real-time observations. FIP is generated for forecast periods out to 12 hours in hourly increments, giving dispatchers a time-evolving, three-dimensional picture of expected icing along a proposed route. Because FIP is model-based, it should always be compared with current pireps and CIP to identify model biases—models sometimes underpredict icing extent in shallow, orographically induced cloud layers.

Dispatchers access CIP and FIP through the AWC website and through most computerized flight planning systems. Outputs are typically displayed as horizontal cross-sections at selected pressure levels (e.g., FL080, FL140, FL180, FL240) or as vertical cross-sections along a route of flight. A dispatcher planning a coastal departure at FL180 in December, for example, would layer the FIP probability and SLD products for that level and time period over the route, identify any ≥40% probability corridors, and cross-check with recent pireps and AIRMETs.

AIRMETs and SIGMETs as Complementary Products

CIP and FIP provide probabilistic, gridded detail that older text products cannot match, but dispatchers still rely on AIRMET Sierra (IFR) and AIRMET Zulu (icing) as regulatory and operational benchmarks. AIRMET Zulu is issued for moderate icing and freezing levels and is typically the floor for dispatch concern. A SIGMET for severe icing not associated with a thunderstorm is issued when conditions are more extreme and carries greater urgency. Under 14 CFR Part 121, a flight release into a forecast of severe icing requires specific aircraft certification—not all transport-category airplanes are approved for flight into known icing (FIKI), and none are approved for intentional flight into severe icing.

Aircraft Certification and Anti-Ice Equipment Basics

A dispatcher cannot assess icing risk in isolation from the specific aircraft on the release. FAA approval for flight into known icing (FIKI) is spelled out in the aircraft's type certificate data sheet and flight manual (AFM). An airplane with FIKI approval has demonstrated, through FAA certification testing under 14 CFR Part 25, Appendix C, that its ice protection system can handle the icing environment defined there. Aircraft with an SLD certification extension (evaluated against Appendix O of Part 25) have additional approval for freezing drizzle and freezing rain environments.

Ice protection systems fall into two broad categories:

Anti-icing systems — prevent ice from forming in the first place. Examples include bleed-air thermal wing leading-edge systems, electrically heated windshields, pitot heat, and heated engine inlets. These systems must be ON before entering icing conditions.
De-icing systems — remove ice after it has already formed. Pneumatic boot systems on smaller turboprops are the classic example; they periodically inflate to crack and shed accreted ice. Some systems are cycled, meaning the crew must allow a small ice buildup before activating to prevent ice bridging, though this practice is aircraft-specific per the AFM.

Dispatchers must know which system type their aircraft carries and confirm that all ice protection equipment is serviceable prior to release. A MEL deferral of a wing anti-ice channel may prohibit flight into known icing entirely, or restrict it to certain conditions—the dispatcher must read the applicable MEL limitation carefully and apply it to the forecast icing environment on the proposed route and altitude.

Dispatch Decision-Making in Icing Conditions

When CIP, FIP, pireps, AIRMETs, and METARs collectively indicate icing along a route, the dispatcher's decision framework involves several questions:

Is the aircraft certified for flight into known icing? If not, the flight may not be released into forecast icing conditions.
Does the forecast include SLD conditions? If so, does the aircraft carry SLD certification? If not, routing or altitude adjustments are mandatory.
Is icing forecast at severe intensity? No transport-category aircraft is approved for intentional penetration of severe icing—an alternate route or altitude must be found.
Are all anti-ice and de-ice components MEL-serviceable for the expected conditions?
Is there a reasonable alternate route or altitude where icing is absent or the aircraft can climb above the icing layer? FIP's vertical cross-section view is invaluable here.
What are the fuel implications of carrying anti-ice bleed air or routing around ice? Bleed-air anti-ice can significantly increase fuel burn—dispatchers must account for this in fuel calculations.

Part 121 dispatchers issue a dispatch release that acknowledges known hazards. If conditions deteriorate en route, the dispatcher has continuing responsibility to communicate updated weather to the crew and, if necessary, amend the release.

Key Numbers and Rules

0°C to −20°C: primary temperature range for structural icing; greatest accumulation rates typically occur between 0°C and −10°C where supercooled liquid water content is highest.
−40°C: approximate temperature below which water droplets spontaneously freeze (homogeneous nucleation); structural icing risk is minimal below this temperature.
SLD droplet threshold: freezing drizzle generally exceeds 50 micrometers median volumetric diameter, while freezing rain droplets are typically larger, often exceeding 100 micrometers up to several hundred micrometers; Appendix O of 14 CFR Part 25 governs SLD certification.
AIRMET Zulu: moderate icing and freezing levels, updated every 6 hours (amendments as needed).
CIP update cycle: hourly.
FIP forecast horizon: up to 12 hours, hourly increments.
Severe icing: no aircraft approved for intentional flight into severe icing; immediate exit required.

Common Test Traps

Confusing CIP and FIP: CIP is an analysis of current conditions; FIP is a model-based forecast. Exams may ask which product to consult for current icing versus forecast icing.
Assuming FIKI approval covers SLD: Standard Part 25 Appendix C FIKI certification does NOT cover SLD (Appendix O). A dispatcher must verify SLD-specific approval separately.
Treating severe icing as manageable: No aircraft is certified for intentional penetration of severe icing. Exam questions sometimes imply that a well-equipped aircraft can handle it—it cannot legally or safely.
Overlooking MEL impacts: A deferred ice protection component can restrict the entire flight from known icing regardless of aircraft FIKI status. Always check the MEL limitation, not just the base certification.
Ignoring fuel burn for anti-ice: Bleed-air thermal anti-icing significantly increases engine fuel flow. Dispatch fuel calculations must account for extended operation of these systems.