Plain English Meaning

ALSF-1 is a specific layout of bright runway approach lights, including a row of fast-flashing lights that appear to race toward the runway, used to help pilots see and line up with a Category I precision runway as they break out of the clouds.

Full Definition

A high-intensity approach lighting system installed at the approach end of a Category I precision instrument runway. It consists of a 2,400- to 3,000-foot centerline bar of steady white lights extending outward from the runway threshold, a 100-foot crossbar of steady lights located 1,000 feet from the threshold, a green threshold light bar, red terminating bars near the threshold, and a series of sequenced flashing white lights (often called the '') that rapidly toward the runway to give a strong -in during the of an .