GCA stands for "Ground Control Approach". It refers to the radar
and the Air Traffic Controllers that use it to guide aircraft to a landing
at an airport. The radar that I worked on had enough resolution that you
could see the individual lights at the edge of the runway as two parallel
rows of dots:
Some Air Traffic Controllers in Germany used to say that GCA really stood for "God's Chosen Airmen" but some of the more cynical or sarcastic pilots claimed that it really meant "Gonna Crash Anyway" which amused some of the Air Traffic Controllers and annoyed some of them severely.
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