Low-flying aircraft or sudden aircraft noise may occur nearby; stay alert and avoid being startled.
The sign warns of aircraft passing low over the road, often near an airfield. Sudden noise may be distracting, so keep your attention on the road.
The United Kingdom 558 shows a black aircraft inside a red-bordered white triangle. Poland A-26 uses an aircraft symbol inside a red-bordered yellow triangle.
Official sign in each country; the code is its number in the national rules. Signs that come in two directions show the left and the right version.
Sign images from Wikimedia Commons, used under their licences.
