Not every approach ends in a landing. Sometimes the pilot climbs away, comes around and tries again. Pilots call this a go-around. The procedure they fly is the missed approach.
Why would a pilot go around?
There are a few common reasons:
- The pilot cannot see the runway. On an approach through cloud, fog or heavy rain there is a point, shown on the approach chart, where the pilot must see the runway clearly enough to land. If they cannot, they go around.
- The runway is not clear. The aircraft ahead has not yet left it.
- The approach is not stable. The aircraft is too high, too fast or not lined up, and the safe thing is to start again.
- The wind. A strong gust or a sudden change in the wind close to the ground.
- Air traffic control tells them to.
A go-around is not an emergency. It is uncommon, and it is routine: every pilot trains for it, and every instrument approach has one published.
A track like any other
The missed approach is a published track, printed on the approach chart. It tells the pilot which way to fly and how high to climb, usually to 3,000 or 4,000 feet, and where to wait for air traffic control to bring them back around. It can go straight ahead or turn. Each runway has its own.
Two parallel runways
An airport with two parallel runways can land aircraft on one while it launches aircraft from the other. Now think about a go-around on the landing runway. The aircraft climbs away just as another aircraft takes off from the runway beside it. Both are climbing, side by side.
ICAO, the UN’s civil aviation body, sets out how to do this safely in its manual on parallel runways. The two tracks must split apart: the departure track must diverge “immediately after take-off, by at least 30 degrees, from the missed approach track of the adjacent approach”.
Think of it as a 30 degree budget. The rule sets the size of the split, not who pays for it. The departure can take all of it, the missed approach can take all of it, or the two can share it. At most airports with parallel runways, all of it goes on the missed approach.
How that choice was made at Dublin is in Motorway in the Sky and in the story How a safety rule became a turn aimed at Ratoath.