Steepest glide slope for an international airport

The international airport with the steepest landing approach is London City Airport, which has a published Instrument Landing System (ILS) glide slope of 5.5 degrees. The plunging approach is required because of the airport's city-centre location, surrounded by tall structures, and its relatively short 1,508-m (4,948-ft) runway.

Modern airports guide pilots in for landings using what's called an Instrument Landing System. There are many components to this, but the most important are a pair of radio transmitters called the "localizer" and the "glide slope". These are positioned at the end of each runway, and generate signals that are beamed out at an angle to mark the ideal approach route.

Both are encoded in such a way that the signal shifts the further the receiver is from the centreline. Modern aircraft have equipment on board that decodes these signals, providing information to the pilots and autopilot systems about the plane's position relative to the ideal approach path. The localizer tells pilots whether they are too far to the left or right, while the glide slope tells them whether they're too high or too low.

Most airports have a glide slope of 3 degrees. There are a few with more extreme published approaches, mostly in the mountains of the Alps and Rockies, but none of these airports handle scheduled international flights.

When it originally opened in 1987, the runway at City Airport was just 1,080 m (3,543 ft) long, requiring a glide slope of 7.5 degrees. This meant that only a handful of fairly small aircraft could land there, and that passengers tended to find the experience alarming. The runway was extended in 1992, allowing a wider (though still limited) number of aircraft to operate there. Even with the upgraded runway, air crews require special training in steep approaches before they are allowed to fly into City.