Keeping an airport open during snow and ice is not simply a matter of sending a plough down the runway. Winter operations combine weather monitoring, rapid snow removal, chemical treatment, runway inspections, contamination measurement, friction awareness, air traffic coordination and a formal reporting system that tells flight crews what kind of braking and directional-control performance they should plan for. At major airports, a runway can be cleared repeatedly through a storm while teams simultaneously inspect taxiways, stands, lighting, signs and aircraft movement areas.[1][2]
The short answer
Airports keep winter operations safe by preventing contamination where possible, removing snow and slush quickly, treating surfaces against ice, inspecting runway thirds, assigning Runway Condition Codes under the ICAO Global Reporting Format, and publishing the resulting information so pilots can calculate takeoff and landing performance. The runway is not judged simply as “open” or “closed”; its condition is continuously assessed and can change several times during a single snow event.[1][3]
Why snow is such a serious runway problem
Aircraft tyres depend on friction and water displacement to generate braking and directional control. Dry snow, wet snow, slush, standing water, compacted snow and ice all behave differently under a tyre. Some reduce friction; others create drag, spray, hydroplaning risk or directional-control problems. The effect also depends on depth, temperature and whether another contaminant lies beneath the visible layer.
A runway can look clear and still be slippery
A thin transparent layer of ice can be more operationally serious than an obvious layer of dry snow. Airports therefore assess the actual surface condition rather than relying on appearance alone. Temperature trends, precipitation type and pilot braking reports can all contribute to understanding whether a seemingly clean surface is deteriorating.
The Global Reporting Format
ICAO introduced the Global Reporting Format, commonly called the GRF, to create a globally harmonised way of describing runway surface conditions. It became applicable internationally in November 2021. The central idea is that the airport reports a Runway Condition Code and contaminant description that flight crews can connect directly to aircraft performance information.[3][4]
Runway Condition Codes run from 6 to 0
Under the Runway Condition Assessment Matrix, a code of 6 represents a dry runway. Lower numbers represent progressively more adverse conditions. Code 5 covers conditions such as frost, wet surfaces and certain shallow snow or slush cases; code 3 can apply to more significant snow contamination or slippery-wet conditions; code 2 covers more than 3 mm of standing water or slush; code 1 applies to ice; and code 0 applies to the most severe combinations such as wet ice or water over compacted snow.[4]
Why the runway is divided into thirds
The condition can vary along the runway. One third may have been recently cleared while another has fresh snow or drifting contamination. The airport therefore assesses and reports each runway third separately. A report might contain three codes such as 5/5/3 rather than one overall number.[2][3]
Why direction matters
If the same physical runway is used in the opposite direction, the order of the thirds reverses. This matters because the first third after touchdown from one direction becomes the final third from the opposite direction. Operational information must therefore match the runway designation actually being used.
The Runway Condition Assessment Matrix
The RCAM links observable surface conditions with expected aircraft braking and directional-control categories. The airport begins with contaminant type, depth and temperature information, then assigns an initial code. Additional credible evidence, including pilot braking-action reports, can support upgrading or downgrading under defined procedures.[2][4]
Why friction numbers alone were not enough
Historically, airports used friction-measuring vehicles extensively to describe contaminated runway conditions. The UK CAA notes that attempts to link measuring-device friction values directly to actual aircraft braking performance proved misleading because different aircraft tyres, anti-skid systems and contaminants do not respond identically.[5] The GRF therefore focuses on observable runway condition and aircraft-relevant performance categories instead of pretending one friction number predicts every aeroplane.
Friction vehicles still have uses
Continuous friction measuring equipment can still be useful for pavement maintenance, rubber-removal assessment and trend monitoring. The key distinction is that airport maintenance information and real-time aircraft braking-performance information are not the same thing.
Snow and Ice Control Plans
The FAA requires certificated airports in relevant climates to maintain formal snow and ice control planning. AC 150/5200-30D provides guidance on staffing, equipment, priorities, runway-condition assessment, removal procedures and reporting.[1] Airports prepare before winter rather than inventing a response after the first storm begins.
Forecasting begins before snow reaches the airport
Airport operations teams monitor meteorological forecasts, pavement temperature and expected precipitation type. Snow beginning at -5°C can create a very different operational problem from rain falling onto a surface already below freezing. Advance warning lets the airport call in staff, fuel equipment and pre-position vehicles.
Pavement temperature matters more than air temperature alone
Ice forms on the runway surface, so pavement temperature is critical. A runway can remain above freezing while the air briefly falls below zero, or remain cold enough for freezing even after air temperature rises. Airports can use embedded or mobile sensors and local forecasts to understand this difference.
Pre-treatment
Where approved and environmentally appropriate, airports can apply anti-icing chemicals before freezing conditions develop. The purpose is to prevent or weaken the bond between ice and pavement, making later mechanical removal easier. Chemicals do not make a runway immune to heavy snowfall and must be compatible with aircraft and pavement materials.
Why ordinary road salt is not the standard answer
Chloride salts commonly used on roads can create corrosion concerns for aircraft and airport infrastructure. Airports therefore use approved airfield de-icing and anti-icing materials such as acetate- or formate-based products where suitable. Material selection follows aviation-specific standards rather than municipal road practice.
Mechanical removal is still the main tool
For significant snowfall, the fastest way to restore pavement is physically removing the snow. Major airports operate fleets of high-capacity ploughs, sweepers, blowers and spreaders. The vehicles can work in coordinated formations so a wide runway is cleared in relatively few passes.
Why one snowplough is not enough
A modern runway can be 45 or 60 metres wide and several kilometres long. A road-style plough clearing one narrow strip at a time would take too long. Airport snow teams use multiple vehicles in echelon formation, each offset from the one ahead, progressively moving snow toward the runway edge.
Echelon ploughing
In an echelon, several ploughs travel side by side but staggered longitudinally. The first moves snow sideways, the next receives and moves that windrow farther, and so on. The formation can clear much of the runway width in one coordinated movement while maintaining safe separation between vehicles.
Runway sweepers
Rotary brooms or high-speed sweepers remove the thin layer left behind by plough blades. This is important because compacted residue can become polished or freeze into a hard layer. Sweeping improves the final surface condition before assessment.
Snow blowers
Blowers are useful when snow banks accumulate along runway and taxiway edges. They collect and throw snow farther away or into trucks. This prevents banks from growing into obstacles, blocking signs or reducing wing and engine clearances.
Where does all the snow go?
Airports need designated snow-storage areas that do not obstruct aircraft operations or create drainage and environmental problems when melting begins. Contaminated snow can contain de-icing chemicals, rubber and fuel residues, so disposal and meltwater management can be regulated.
The runway cannot always remain open during clearing
Snow-removal vehicles need room to operate safely. Air traffic control therefore coordinates temporary runway closures or gaps between movements. A busy airport may alternate runways, clear sections in carefully planned windows or suspend operations briefly while the snow fleet makes a complete pass.
Runway occupancy matters
Ten large snow vehicles travelling in formation can occupy the runway for several minutes. Controllers need to know the location of the convoy and ensure every vehicle has vacated before releasing the runway to aircraft. Winter operations therefore demand close communication between airport operations and ATC.
Vehicle visibility in snow
Heavy snow can reduce visibility and obscure taxiway markings. Snow vehicles use high-intensity beacons, radios, transponders or surface-surveillance equipment where required. FAA winter-operations guidance specifically addresses the challenges airport vehicle drivers face during snow and ice operations.[6]
Runway lights must stay visible
Snow can cover inset centreline lights, edge lights and touchdown-zone lights or pile around elevated fixtures. Clearing operations therefore include the lighting system and surrounding areas, not just the tyre path. Lighting inspection becomes especially important in low visibility.
Signs and markings can disappear
A heavy snowfall can hide painted taxiway and runway markings. Airports rely more heavily on lighting, signs, known pavement geometry and surface guidance systems until markings are visible again. Clearing priorities therefore extend beyond the runway itself.
Taxiways can become the bottleneck
A perfectly cleared runway is useless if aircraft cannot reach it. Airports clear priority taxi routes, high-speed exits and access routes between terminals and runways. Lower-priority taxiways may remain closed while the core network is kept operational.
Aprons and stands
Terminal areas contain parked aircraft, ground equipment, fuel pits and passenger bridges, making snow removal more difficult than on an open runway. Snow teams may use smaller equipment and coordinate closely with airlines to prevent ploughed snow from blocking stand guidance or service routes.
Engine ingestion risk
Loose snow and ice near running engines can be ingested or blown into surrounding equipment. Airports and airlines manage snow piles and engine-power use during ground movement to reduce foreign-object and visibility hazards.
Aircraft de-icing is a separate operation
Clearing the runway does not remove snow or ice from the aircraft itself. An airliner must also have critical aerodynamic surfaces free from unsafe contamination before takeoff. Aircraft de-icing and anti-icing are performed by airline or contracted ground teams using approved fluids and procedures.
Why the clean-aircraft concept matters
Even a small amount of rough frost or ice can reduce lift and increase drag. Ground icing rules therefore require crews to ensure wings and other critical surfaces satisfy the aircraft’s approved condition before departure. A clean runway does not compensate for contaminated wings.
Holdover time
Anti-icing fluid provides temporary protection against accumulating precipitation. Its expected protection period is described by holdover guidance that depends on fluid type, concentration, temperature and precipitation. If conditions change or the time expires, the aircraft may need another inspection or treatment.
Airport snow removal and aircraft de-icing interact
A flight can be fully de-iced and ready to leave but then wait for a runway-clearing cycle. That delay consumes holdover time. Airports therefore coordinate de-icing pads, departure queues and runway availability to reduce unnecessary repeat treatment.
Runway contamination depth
The depth of water, slush or snow affects aircraft performance. Under the GRF, 3 mm is an important threshold for several contaminants. For example, more than 3 mm of standing water or slush maps to a Runway Condition Code 2 in the standard matrix.[4]
Why slush is particularly demanding
Slush combines liquid water and ice particles. Tyres have to displace it, creating significant drag and spray. It can reduce acceleration during takeoff and braking during landing while also creating ingestion and directional-control concerns.
Standing water
Water deeper than the tyre can efficiently disperse can lead toward dynamic hydroplaning, where part of the tyre loses direct contact with the pavement. Grooved pavement helps drainage, but deep water can still reduce braking substantially.
Compacted snow
Compacted snow behaves differently depending on temperature. ICAO’s matrix distinguishes colder compacted snow from warmer compacted snow because the friction characteristics change as the surface approaches melting conditions.[4]
Ice
Plain ice is associated with Runway Condition Code 1 under the standard matrix, corresponding to poor braking. Wet ice and certain layers of water or snow over ice can result in code 0, indicating minimal or uncertain braking and directional control.[4]
Code 0 is extremely restrictive
A runway condition code of 0 represents the most adverse category in the GRF and can make normal aircraft operations impractical or prohibited depending on aircraft performance and operator limitations. Airports work aggressively to remove or treat those conditions rather than simply report them indefinitely.
Pilot braking-action reports
Flight crews can report how braking and directional control actually felt after landing. Reports use standard terms such as GOOD, GOOD TO MEDIUM, MEDIUM, MEDIUM TO POOR and POOR. These observations provide real aircraft feedback that airport operations can use when reassessing the surface.[4][5]
Why pilot reports are not perfect measurements
A braking report depends on aircraft type, landing weight, brake use, reverse thrust, touchdown point and pilot perception. One aircraft may not use maximum braking at all. The report is therefore valuable operational evidence but not a laboratory friction coefficient.
Downgrading a runway condition code
If credible evidence indicates braking is worse than the surface-description-based code suggests, the airport can downgrade the reported code using the approved process. This protects crews from relying on an optimistic assessment when real-world braking has deteriorated.
Upgrading is more controlled
Because an unjustified upgrade could overstate runway performance, the GRF sets specific conditions for upgrading. Airports need supporting evidence rather than simply deciding that a runway “feels better.”
SNOWTAM and operational reporting
Runway condition information is distributed through structured aeronautical information including SNOWTAM where applicable and airport/ATC systems. The report can include runway condition codes, contaminant coverage, depth and additional information relevant to flight operations.[3]
ATIS
Important runway condition information can also be broadcast through the airport’s Automatic Terminal Information Service. Pilots receive current runway, weather and operational information before arrival or departure and use it in performance calculations.
Takeoff performance changes
Contamination can increase rolling resistance and reduce acceleration. It can also affect the distance needed to stop after a rejected takeoff. Crews therefore use aircraft performance data matched to the reported runway condition rather than assuming the dry-runway calculation remains valid.
Landing performance changes
Lower braking action increases stopping distance. Airlines may apply operational landing-distance factors beyond certified performance, and the required margins depend on regulation and aircraft type. A runway that remains physically open can therefore be unusable for a particular flight if performance requirements cannot be met.
Crosswind limits can decrease
Directional control becomes more difficult when tyre friction is poor. Aircraft manufacturers and operators can therefore impose lower crosswind limits on contaminated runways. A runway long enough for braking may still be operationally unsuitable because of wind and surface condition together.
Why airports sometimes close before the runway looks terrible
The airport may need an uninterrupted period to clear the surface properly, visibility may be too low for safe snow-vehicle operation, braking may have fallen below acceptable levels, or snow banks may be approaching limits. A proactive closure can restore a safer surface faster than trying to operate continuously through deteriorating conditions.
Snow banks can become obstacles
Ploughed snow cannot simply be pushed indefinitely toward the runway edge. High banks can interfere with wings, engines, signs and navigational equipment. Airports manage maximum snow-bank profiles and remove accumulated snow as necessary.
ILS and navigation equipment
Instrument Landing System critical and sensitive areas contain antennas that cannot be damaged or blocked by snow-removal activity. Crews working near navigation aids need defined routes and restrictions. Snow can also cover equipment access roads used by technicians.
Runway end safety areas and shoulders
Snow removal extends beyond the central pavement. Shoulders, runway ends and safety areas may need treatment so an aircraft that deviates from the centreline does not encounter an abrupt snow ridge. Airports define priorities according to local layout and operating needs.
Drainage remains important in winter
Snow eventually melts. Poor drainage can turn cleared snow into standing water and then refreeze it later. Runway grooves, transverse slope and drainage systems therefore remain part of winter safety even after the ploughs have finished.
Refreezing
A runway can deteriorate after precipitation stops. Meltwater may refreeze as temperature falls, especially around shaded areas, joints or low spots. Continued inspection is therefore required even during apparently improving weather.
Freezing rain
Freezing rain can create a rapid glaze of ice on runways, taxiways, aircraft and ground equipment. It is among the most challenging conditions because contamination can reform quickly after treatment. Operations may be heavily restricted until the weather changes.
Blowing and drifting snow
Strong wind can move previously cleared snow back onto the runway. Drifts can form unevenly and reduce visibility. Snow fences, repeated patrols and continued ploughing may be required even when fresh snowfall has stopped.
Why major airports invest heavily in snow fleets
Every prolonged runway closure can disrupt hundreds of flights, passenger connections and aircraft rotations. High-capacity snow equipment is expensive but can pay for itself by reducing closure time during major winter events. Airports in cold climates therefore maintain specialised fleets far beyond what an ordinary road authority would use on one strip of pavement.
Staffing is part of capacity
A fleet of 30 vehicles is useless without trained drivers, mechanics, supervisors and operations inspectors. Airports maintain winter rosters and recurrent training so enough qualified personnel are available during storms that may last through the night.
Equipment reliability
Snowploughs operate in cold, corrosive and high-load conditions. Preventive maintenance, spare blades, tyres, hydraulic parts and fuel reserves are part of winter readiness. Airports test equipment before the season because breakdowns during a heavy storm immediately reduce clearing capacity.
Training drivers for the movement area
Snow crews may work on active runways and taxiways where navigation mistakes can create runway incursions. Drivers need radio competence, airfield familiarity and understanding of ATC phraseology. The FAA highlights winter vehicle operations as a specific airfield-driver training concern.[6]
Surface surveillance
At equipped airports, surface radar or multilateration can help controllers track snow vehicles during poor visibility. This does not replace radio discipline, but it adds situational awareness when visual observation from the tower is limited.
Why winter capacity falls even when the airport stays open
Runways need periodic clearing, taxi speeds may be lower, aircraft require de-icing, runway exits may be unavailable and greater spacing may be used. The result is fewer aircraft movements per hour. An airport can therefore remain technically open while schedules experience significant delay.
Airline schedule recovery
When capacity falls below scheduled demand, airlines may cancel selected flights rather than allow every flight to accumulate uncontrolled delay. This creates space for the remaining operation and helps prevent aircraft and crews from becoming stranded throughout the network.
Why a cleared runway can close again 20 minutes later
Heavy snowfall can cover the surface rapidly. A runway assessed as code 5 after clearing may deteriorate as new snow accumulates. Airports repeatedly inspect and reassess the surface, meaning a condition report has a limited useful life during active precipitation.
Continuous monitoring
The GRF is not a once-per-shift report. Airport operators are expected to reassess when conditions change and report updated information without undue delay.[2][3] Pilots therefore seek the most recent report rather than relying on conditions from an earlier arrival.
Why winter operations are a system problem
A snowy runway affects airport operations, ATC, aircraft performance, airline dispatch, ground handling and passenger schedules simultaneously. The safest result depends on every part of that chain using the same current description of the surface and coordinating around the same clearing plan.
The engineering lesson
The important fact is that airports do not try to create an abstract “perfectly dry” runway at all times. They manage contamination as a measurable operational condition. Mechanical equipment removes as much contamination as practical, chemical treatment prevents or weakens ice, inspectors classify what remains, and the GRF translates that physical surface into information aircraft crews can use for performance.
Conclusion
Snow and ice operations are one of the clearest examples of an airport functioning as an engineering system rather than simply a place with a runway. Fleets of ploughs and sweepers may clear kilometres of pavement repeatedly through a storm, but the physical cleaning is only half the job. The airport must then assess each runway third, assign condition codes, publish contaminant information and keep monitoring as weather changes. Pilots use that report to calculate whether their aircraft can safely take off or land. The result is a continuous loop: observe, clear, assess, report and repeat until the winter weather finally moves on.
Sources / Technical References
- [1] FAA, AC 150/5200-30D — Airport Field Condition Assessments and Winter Operations Safety — https://www.faa.gov/airports/resources/advisory_circulars/index.cfm/go/document.current/documentNumber/150_5200-30
- [2] UK Civil Aviation Authority, CAP 2174 — Assessment, Measurement and Reporting of Runway Surface Conditions for Licensed Aerodromes — https://www.caa.co.uk/data-and-publications/publications/documents/content/cap2174/
- [3] ICAO, Global Reporting Format for Runway Surface Conditions — https://www.icao.int/new-global-reporting-format-runway-surface-conditions
- [4] ICAO, Global Reporting Format Runway Condition Assessment Matrix — https://www.icao.int/safety/SiteAssets/Pages/GRF/RCAM%20Poster_v1.0.pdf
- [5] UK CAA, Contaminated Runway Reporting System / Global Reporting Format — https://www.caa.co.uk/commercial-industry/aerodromes/aerodrome-safety/runways/contaminated-runway-reporting-system/
- [6] FAA, Airfield Drivers — Winter Operations Safety — https://www.faa.gov/airports/runway_safety/airfield_drivers
- [7] Unsplash, Illán Riestra Nava, “an airport tarmac covered in snow next to a runway” — free to use under the Unsplash License; selected as this article’s unique feature photograph — https://unsplash.com/photos/an-airport-tarmac-covered-in-snow-next-to-a-runway-7MASRJ31BUw
Disclaimer: Cockpit King provides general aviation education and reference information. Winter operations, runway-condition assessment, chemical treatment, aircraft de-icing and performance limitations vary by airport, aircraft, operator and jurisdiction. Current approved airport procedures, aircraft performance data, NOTAM/SNOWTAM information and regulatory requirements always take precedence. This article is not winter-operations or flight-performance instruction.