Airport winter operations: runway clearing, braking action and snow plows

Overnight, twenty centimeters of fresh snow have fallen, the first long-haul jet is due just after six – and it still lands on time. Behind that is one of the most elaborate routines in airport operations: airport winter operations. They clear runways, taxiways and aprons, keep them free of ice and finally assess how well an aircraft can brake on the runway. This guide explains how the clearing works, which vehicles you see doing it, what is behind the runway condition code from 0 to 6 and how to plan a winter day at the fence sensibly.

Airport winter operations: the short answer

Winter operations have three jobs: remove snow, prevent ice and assess the condition of the surfaces. Clearing is done with convoys of plows, sweeper-blowers and snow blowers, and airport-grade deicers help against ice. Afterward, staff assess the runway and assign each third a runway condition code (RWYCC) from 0 to 6. Cockpit crews receive this report and use it to calculate whether and how they can take off or land.

The difference from a road is important: on a highway it is enough if the roadway is drivable. On a runway, an aircraft has to touch down at high speed and come to a stop within a calculated distance. Every bit of leftover snow and every sheet of ice changes that calculation. That is why airport winter operations are not a side job but part of flight safety.

Everything that has to be cleared

When you think of winter operations, you think of the runway. In reality it is only one part of the work. An airport has to keep several types of surface clear at the same time, and they have different priorities:

• Runways: Highest priority, because the highest speeds occur here. Besides the runway itself, the edge areas are included so that engines do not ingest chunks of snow and the lighting stays visible.
• Taxiways: They connect the runway and the apron. Without cleared taxiways, even the best runway is useless. How taxiways are named and signed is explained in the article Taxiways, holding points and signs.
• Apron and parking positions: Aircraft, tugs, fuel trucks and buses stand close together here. Clearing is often coordinated with ground handling, because positions are rarely free for long. More on this in the guide to gates and remote stands.
• Lighting and signs: In-pavement lights along the runway centerline and edge lights have to stay clear, otherwise there are no reference points in poor visibility. The article on runway and taxiway lighting shows which lights exist.
• Service roads and access roads: Fire and rescue services also have to be able to get everywhere at all times. The requirements for the airport fire service apply in winter just the same.

Airports with several runways have an advantage: they can clear one runway while flights continue on the other. At airports with only one runway, every clearing is a real interruption of operations. What closed runways mean for spotters is described in the article on runway closures and construction work.

The clearing vehicles: what you see at the fence

When a clearing convoy rolls onto the runway, you quickly see that these are no ordinary road vehicles. The machines are wider, heavier and built for high working speeds.

Vehicle type	Job	How to recognize it
Snow plow	pushes snow aside in a single pass	very wide, angled blade at the front
Sweeper-blower	brushes with a roller and blows residual snow away with a powerful airstream	plow at the front, a transverse brush roller under the vehicle, blower behind; often trails a cloud of snow
Snow blower	picks up snow banks and throws them far to the side into the field	rotating cutter drum at the front and a discharge chute with a tall plume of snow
Spreader truck	applies liquid or granular deicers	tank or hopper, spray bar or spreader disc at the rear
Measuring vehicle	checks runway condition and friction	usually a smaller vehicle, sometimes with a measuring wheel or measuring trailer

The sweeper-blowers are the real stars of airport winter operations. They combine plow, brush roller and blower in one vehicle and leave a very clean surface. The combination matters because even thin remnants of snow can freeze solid in frost.

A single machine cannot cover the width of a runway. Airport snow plows with wing extensions are far wider than road plows, but it still takes several vehicles to clear a runway more than 40 meters wide. That is why they work as an echelon: staggered diagonally one behind the other, with each vehicle taking over the snow from the one ahead and pushing it a bit further toward the edge.

How runway clearing works

Behind the clearing is precise coordination between the airport operator, air traffic control and airlines. At most airports the process follows a similar pattern.

In heavy, persistent snowfall, large airports sometimes alternate runways: while one is being cleared, flights use the other. For you at the fence, that means the active runway can change several times a day – similar to a change of runway direction in use, just for a different reason.

Deicers instead of road salt

On roads, salt is the go-to solution. At the airport it is taboo, at least on airside surfaces. Chlorides such as sodium, calcium or magnesium chloride are highly corrosive and would attack landing gear, brakes and structural components.

Instead, airports rely on agents such as potassium acetate or formates. They are far less corrosive and put less strain on soil than chlorides. They are applied as a liquid, as granules or in combination. Liquid agents work quickly and are well suited for prevention, while granules penetrate an existing layer of snow or ice better.

Do not confuse surface deicing with the deicing of the aircraft themselves. Aircraft have their own fluids and procedures on dedicated deicing pads. How that works and what colors the fluids have is explained in the article on aircraft deicing.

Braking action: from friction values to the runway condition code

For crews, one question counts in the end: How well does the aircraft brake on this runway? For a long time there were very different procedures for answering it. That has changed.

The old system: measured friction values

Many European airports used to report a measured friction coefficient. A measuring vehicle drove down the runway and determined the grip for each third. The values were translated into levels:

Friction value (old)	Braking action
0.40 and above	good
0.36 to 0.39	medium to good
0.30 to 0.35	medium
0.26 to 0.29	medium to poor
0.25 and below	poor

The procedure had weaknesses. Measuring devices from different manufacturers gave different values on the same surface. The measuring wheel is not an aircraft tire; it is lighter and travels slower than a landing aircraft. And a measurement only shows the condition at that moment – if snow starts falling again afterward, the value is quickly outdated.

The new system: Global Reporting Format

Since November 4, 2021, ICAO’s Global Reporting Format (GRF) has applied worldwide. The start was originally planned a year earlier but was postponed because of the COVID-19 pandemic. The core of the GRF is a uniform assessment: trained staff assess each runway in three sections and assign each third a Runway Condition Code (RWYCC) from 0 to 6. The basis is a globally agreed assessment matrix, the Runway Condition Assessment Matrix (RCAM).

The codes depend mainly on the type and depth of the contaminant, plus the temperature. Roughly, the scale can be read like this:

Code	Typical surface	Braking action
6	dry	–
5	wet or with a very thin layer of frost, snow or slush	good
4	compacted snow at very low temperatures	good to medium
3	slippery when wet, compacted snow, deeper snow	medium
2	standing water or slush of significant depth	medium to poor
1	ice	poor
0	wet ice, water on top of compacted snow, snow on top of ice	less than poor

The table summarizes the matrix in simplified form. In practice, staff can adjust a code based on further observations, such as pilot reports on braking action. Together with the type, depth and coverage of the contaminant, the three codes make up the Runway Condition Report (RCR).

How the report gets to the cockpit

The Runway Condition Report reaches crews in several ways: through the SNOWTAM, a special NOTAM message for snow, ice, slush and water on airside surfaces, through the automatic broadcast ATIS and, if needed, directly by radio. How such messages are structured is shown in the guides Reading NOTAMs and ATIS explained. Pilots compare the codes with their aircraft’s performance data and use them to calculate whether the available runway length is enough. Weather reports such as METAR also contain hints about snowfall and visibility – how to decode them is covered in the guide Reading METAR and TAF.

For heavy long-haul jets, a low code can mean they take off only with a reduced payload or divert to a longer runway. With a crosswind it gets tighter still, because a slippery runway offers less lateral control. Why that is so is explained in the article on crosswind landings.

Airports with winter experience

How well an airport copes with snow depends heavily on its experience. Airports in northern Europe such as Helsinki, Oslo or Stockholm Arlanda have long winters and correspondingly large clearing fleets and well-rehearsed procedures. Snow is normal operations there, not a state of emergency. The same applies to airports such as Rovaniemi in Lapland or Anchorage in Alaska.

In the Alps and southern Germany, snow days are also part of winter, for example at Munich Airport or Zurich Airport. It often gets harder where snow rarely falls: an airport that is only properly snowed in every few years generally keeps less equipment on hand. When the snow does come, delays and cancellations are more likely.

Wherever the airport is, the runway alone does not decide whether operations run. The deicing of aircraft, cleared apron positions and ground staff all have to play along. Often aircraft deicing is the real bottleneck, not the runway.

What winter operations mean for your spotting day

For spotters, a snow day is an opportunity and a challenge at the same time. The key points at a glance:

Whether your spot works on a snow day depends mainly on the runway direction in use and on which runway is currently free. An elevated vantage point such as the Munich Airport visitors’ hill (Besucherhügel) or a terrace such as Observation Deck B in Zurich has the advantage that you overlook a larger part of the airport and can follow clearing convoys better. How to protect yourself and your camera against the cold is covered in the guide Plane spotting in winter. General tips for gloomy days are in Plane spotting in bad weather.

What to watch out for

• Check the weather forecast and read the METAR. Snowfall, temperature and wind decide whether and when clearing happens. Map services help with the assessment – tips are in the article on Windy and other weather maps.
• Expect runway changes. When a runway is cleared, traffic can switch to another one at short notice. Plan a backup spot.
• Keep your distance from clearing vehicles. Even outside the fence, winter service vehicles travel on service and access roads. Do not park on clearing routes or in front of gates.
• Stay on the right side of the fence. Snow banks can make fences look lower. Entering the grounds is still prohibited and can be expensive, as the article on trespassing on airport grounds shows.
• Take the cold seriously. Waiting for hours in snow and wind chills you quickly. Keep spare batteries warm and plan breaks in the car or terminal.
• Factor in slippery paths. Spotter hills and dirt tracks are often not cleared at all. Sturdy shoes with good tread are a must.

Common misconceptions

“The airport is shut when it snows.” In most cases it is not. Large airports keep clearing continuously even in persistent snowfall and maintain operations at reduced capacity. Delays more often come from aircraft deicing and ground processes than from the runway itself.

“A cleared runway is a dry runway.” Even after clearing, remnants, moisture or ice can remain. That is exactly why the runway condition code exists. A code of 5 means good braking action, but not a dry runway.

“Braking action is purely a measured quantity.” In the old system, friction values were the focus. In the GRF, the code is based on a standardized assessment of the surface. Measurements and pilot reports feed in as additional information.

“Clearing is quick.” A clearing convoy does move briskly, but closing, clearing, follow-up treatment and assessment take time. In heavy snowfall, a runway that has just been finished often has to be cleared again after a short time.

Conclusion

Airport winter operations are a well-rehearsed system of clearing convoys, airport-grade deicers and a standardized condition assessment. Since 2021, a worldwide uniform code from 0 to 6 describes for each runway third how well an aircraft can brake. For you as a spotter, that means: clearing phases bring breaks and runway changes, but they also offer subjects you never get in summer. If you check the weather, runway direction in use and accessibility of your spot beforehand, you turn a snow day into a special spotting day.