At Ruzyně, fog hid the end of the runway, yet landing was still allowed

01Runway

In fog, what matters is which way the aircraft approaches the runway

A precision approach guides the aircraft by instruments, both sideways and vertically. The categories CAT I, II and III set how low an aircraft may descend with this guidance and what minimum runway visual range (RVR) it needs.

Prague Airport lists CAT III B for runway 24, while runways 06, 12 and 30 have only CAT I. Runways 06 and 24 are one and the same concrete runway, and the numbers only say from which end aircraft approach it. CAT III therefore applies only to approaches in the 24 direction.

When choosing the runway in use, Prague Airport gives preference to runway 24, followed by runways 06, 30 and 12. The highest category and the highest preference therefore fall on the same direction.

02Approach

The pilot only needs to see the runway at decision height

Three steps to touchdown

1. 01

   ILS guidance

   The instruments keep the aircraft on the runway centreline and on the glide path, even when almost nothing is visible from the cockpit.

2. 02

   Descent to decision height

   For CAT II and III, decision height is measured by a radio altimeter, that is, directly above the ground. Without a reported runway visual range, the crew may not fly such an approach.

3. 03

   The landing decision

   If the crew sees runway lights or markings at decision height, it continues to land. Otherwise it starts a missed approach and climbs again.

The visibility in a METAR report applies to the surroundings of the airport. Runway visual range (RVR) tells how far a pilot on the runway centreline can see its markings or lights. RVR takes precedence when the minima are assessed, and below the minimum the crew will usually not start a precision approach at all.

Instruments do not measure runway visual range directly, a system calculates it. The calculation takes in the clarity of the air, the faintest light the eye can still detect and the intensity of the runway lights.

In a CAT III approach, the aircraft can land by itself. The crew monitors the automatic system and abandons the approach if problems arise. Besides an equipped runway, the aircraft and its crew must also hold the necessary approval.

03History

Without an equipped runway, fog stops Ruzyně

How much fog restricts traffic depends on which runway the airport can use at the time. Two earlier mornings at Ruzyně show this, in April 2008 and in April 2025.

On the morning of 16 April 2025, the main runway 06/24 was under repair and aircraft used the secondary runway 12/30, which does not allow operations in reduced visibility. According to Novinky.cz, air traffic control did not permit take-offs or landings at an RVR below 550 metres at any measuring point. The airport stopped arrivals and departures at around 5:00, and the restriction lasted five hours.

By 10:00, according to the airport's spokeswoman, the fog had affected 24 arrivals and six flights were cancelled outright. At 9:30, runway 12/30 still had a runway visual range of only 275 metres, and by 10:00 the visibility according to ATIS was 2000 metres.

On the morning of 5 November 2026, the METAR for runway 24 reported an RVR of 325 metres at 8:00 CET, below the 550 metre limit from April 2025. For CAT II, however, 300 metres is enough, and according to Letiště Praha runway 24 has an even higher category. Fog with such a runway visual range does not in itself rule out landing there.

04Fog

The fog over the airport was not equally thick everywhere

Fog is often patchy. On the morning of 5 November 2026, the METAR at Ruzyně reported it alternately as patches of fog (BCFG) and, at its thickest, as freezing fog (FZFG). Freezing fog is made of water droplets that stay liquid below zero.

Instruments determine runway visual range at several points along the runway, for a CAT III runway at the touchdown zone, the midpoint and the end. Every runway has different surroundings, so patchy fog can wrap one runway while leaving another almost clear.

At 5:00 CET the report gave the runway visual range for runway 06, and from 5:30 CET for runway 24, which is the opposite direction of the same runway. A value above 2000 metres for runway 30 does not mean aircraft were landing on it, only that visibility there was better.

At 8:30 CET the METAR reported a visibility of only 200 metres, yet the runway visual range on runway 24 was already 1600 metres and rising. The difference shows how little the visibility in a report says about conditions on the runway.

05Journey

Before you head to the airport

Fog can delay flights even on a well-equipped runway. Before you travel, check your flight status with the airline or on the airport website, and look at the weather expected where you are.

The local Fakt počasí forecast shows temperature, precipitation and wind with gusts hour by hour, and humidity and dew point in the current conditions. When the temperature gets close to the dew point, the air is almost saturated with water vapour. The forecast does not, however, announce fog itself.