Winter Operations in Aviation
Deicing, holdover time, runway contamination · Sources: FAA · EASA · NOAA · ICAO Annex 6 · SAE AMS
Winter flying introduces three big variables: contamination on the aircraft (frost, snow, ice on wings and control surfaces), contamination on the runway (snow, slush, ice — affecting braking and takeoff performance), and visibility / approach minima (snow, freezing fog). The aviation system absorbs these with codified procedures: deicing with Type I fluid, anti-icing with thickened Type II / III / IV fluids, holdover time tables published annually by the FAA, runway condition reports under the global RCAM (Runway Condition Assessment Matrix), and performance penalties for contaminated runways. The result is more delay, not more risk — but every minute on the deicing pad is a minute the gate is held.
Why aircraft need deicing
Frost, snow, or ice on the wings disrupts airflow. Even a thin layer can degrade lift by 30% or more, increase stall speed, and change pitch behavior at rotation. The principle is captured in the "clean aircraft concept" — codified in FAA AC 120-60 and EASA AMC 25-9 — which prohibits takeoff with any frozen contaminant on critical surfaces (wings, control surfaces, propellers, engine intakes, tail).
Two distinct operations:
- →Deicing — remove contamination already on the aircraft. Usually heated Type I fluid sprayed at pressure.
- →Anti-icing — apply a thicker fluid (Type II / III / IV) that adheres to surfaces to prevent ice forming during taxi and pre-takeoff. The fluid sheds at rotation speed.
Deicing fluid types
| Type | Color | Function | Holdover |
|---|---|---|---|
| I | Orange | Heated, Newtonian (no thickener). Used for deicing. | 1–22 min |
| II | Yellow / straw | Thickened. Anti-icing, sheds at rotation. Higher-rotation aircraft. | up to ~80 min |
| III | Yellow / amber | Thickened, optimized for lower-rotation aircraft (~60 kt). | varies |
| IV | Green | Thickened, the longest-protection anti-icing fluid in common use. | 9–160 min |
All fluids are glycol-based (propylene or ethylene). They meet SAE AMS specifications (AMS1424 for Type I; AMS1428 for Types II/III/IV).
Holdover Time (HOT)
Holdover Time is the time, after application of an anti-icing fluid, during which the fluid is expected to keep the protected surfaces free of frost, ice, or snow accumulation. HOT depends on:
- →Fluid type and concentration (100/0, 75/25, or 50/50 fluid/water)
- →Outside Air Temperature (OAT)
- →Type and intensity of precipitation (very light snow, snow, heavy snow, freezing rain, freezing drizzle, freezing fog)
The FAA Holdover Time Guidelines (Winter 2025-2026), published August 12, 2025, provide the official tables crews use. Each cell gives a time range — the crew uses the lower bound under heavy precipitation, the upper bound under lighter conditions.
If the holdover expires before takeoff, the aircraft must be re-treated. A "pre-takeoff contamination check" by the crew is required regardless: visual confirmation that critical surfaces remain clean.
Two-step deicing — when one pass isn't enough
For heavy contamination or low temperatures, operators use a two-step procedure:
- Step 1 — Deice with hot Type I (or water/Type I mix) to remove contamination.
- Step 2 — Anti-ice with Type II/III/IV (often within 3 minutes of Step 1) to protect the aircraft during taxi.
A combined "one-step" with Type II/III/IV alone is used when only anti-icing protection is needed.
Runway contamination and RCAM
A contaminated runway changes both braking action and takeoff performance. ICAO standardized the global reporting framework in 2021: the Runway Condition Assessment Matrix (RCAM). Airports report a Runway Condition Code (RWYCC) from 6 (dry) to 0 (less than poor braking).
| Code | Surface | Braking |
|---|---|---|
| 6 | Dry | Good |
| 5 | Wet / frost | Good |
| 4 | Slush / wet snow ≤3 mm | Good to medium |
| 3 | Compacted snow / dry snow >3 mm | Medium |
| 2 | Slush / standing water / wet ice with sand | Medium to poor |
| 1 | Ice | Poor |
| 0 | Wet ice / water on compacted snow / dry snow over ice | Less than poor — operations may stop |
Reported in the RCR (Runway Condition Report). Crews use it as an input to performance calculations.
Takeoff and landing performance penalties
Aircraft performance tables include separate columns for contaminated runways. Penalties accumulate quickly:
- →Takeoff distance increases — slush adds rolling friction; the aircraft accelerates slower
- →V1 (decision speed) is reduced to keep stopping distance within runway length
- →Landing distance can roughly double on a contaminated runway versus dry
- →Crosswind limits are reduced; some airlines publish dedicated wet/snow crosswind tables
On a marginal day a flight may be weight-restricted (offloading cargo or passengers) or the dispatch may select a different runway or destination.
Why winter causes ground delays
The visible "deicing delay" is the sum of several inputs:
- →Deicing pad capacity — limited number of bays, limited trucks
- →Holdover constraint — must depart within the HOT window or return for retreat
- →Runway switches and plowing — sweepers and brooms run between rolls of departures
- →Reduced acceptance rates — ATC reduces departure/arrival flow under low-visibility procedures (LVPs / CAT II / III)
- →Crew time — duty-time limits triggered by long ground holds
The "perfect storm" is a busy hub with snow, low visibility, and only some runways open: arrivals back up, departures queue for deicing, and downstream cancellations propagate through the day's rotations.
Major winter-hub procedures
Centralized deicing pads adjacent to runways. Lake-effect snow events drive ground stops; FAA Ground Delay Programs are routine in heavy events.
Nor'easters bring heavy wet snow and freezing rain. Gate-side and remote pad deicing both in use; long taxi distances stress HOT windows.
Centralized deicing infrastructure with high throughput; one of Europe's largest winter-ops operations. Routine LVPs in winter fog.
Alpine inversion fog and snow. Strict deicing pad sequencing; ATC flow regulations from EUROCONTROL Network Manager.
Two parallel runways with dedicated deicing positions. Heavy snowfall events drive cancellations rather than long holds.
Canadian airports operate among the largest centralized deicing facilities in the world; Toronto Pearson's Central Deicing Facility (CDF) has 12 bays.
What passengers see vs what's happening
The aircraft is going to a dedicated deicing area, not directly to the runway. Adds 15–60 minutes typically.
Working as designed. The fluid is doing its job; it sheds during takeoff roll.
Holdover time expired before takeoff, or a contamination check revealed accumulation. Standard procedure.
A different runway may have been cleared or has more favorable wind for performance on a contaminated surface.
Sources
- FAA Holdover Time Guidelines Winter 2025-2026 — original issue 12 August 2025
- FAA AC 120-60 — Ground Deicing and Anti-Icing Program
- EASA AMC 25-9 — Subsonic Aeroplanes, Aerodynamic Stability and Control
- ICAO Annex 6 Part I — operator deicing and contaminated-runway requirements
- ICAO Doc 9981 — PANS-Aerodromes (RCAM / RWYCC framework)
- SAE AMS1424 (Type I) and AMS1428 (Type II/III/IV) — fluid specifications
- NOAA NWS — winter aviation weather products (TAFs, AIRMET ZULU)
- NBAA — operator-side guidance on deicing program updates