Definition
A high-intensity approach lighting system installed at runways serving Category II and Category III precision instrument approaches. It consists of a centerline bar of steady-burning white lights extending 2,400 feet from the runway threshold, a 1,000-foot crossbar, red side row barrettes for the final 1,000 feet, a green threshold bar, and a series of sequenced flashing white lights that travel rapidly toward the runway, giving the pilot a strong visual lead-in during low-visibility approaches.
Plain English
It is the most capable runway approach lighting layout. As the pilot breaks out of cloud near the runway, a long line of bright white lights — with a moving 'rabbit' of flashes running toward the runway — points the way to touchdown.
Context Anchor
Seen on instrument approach charts, airport lighting information, and runway descriptions for airports equipped for low-visibility arrivals.
Derivation
The 'sequenced flashing' part comes from the lights firing one after another in a fast sequence rather than all at once. Pilots commonly call this effect 'the rabbit' because the flash appears to run along the ground toward the runway.
Why Pilots Care
Provides essential visual guidance for runway alignment and safe touchdown when the runway itself may not yet be visible.
Grounding Statement
On final approach in poor visibility, the sequenced flashing lights appear to move toward the runway, drawing the pilot’s eyes to the runway threshold.
Intuition Check
Do not picture random flashing lights. In ALSF-2, the lights flash in a planned order toward the runway to guide the pilot’s eyes in the correct direction.
Example Sentence 1
The captain briefed that the runway was equipped with ALSF-2, so they could expect a strong visual lead-in even in low visibility.
Example Sentence 2
Airport maintenance confirmed the ALSF-2 system was operational before the Category II approach began.