Definition
SALS and SALSF are two related runway approach lighting systems installed on the approach end of certain instrument runways. SALS consists of a configuration of steady-burning white lights extending outward from the runway threshold for 1,500 feet, providing visual guidance to pilots transitioning from instrument to visual flight on final approach. SALSF is the same physical layout as SALS but adds sequenced flashing lights -- a series of lights that flash in rapid succession toward the runway threshold, creating a visual 'rabbit' that helps the pilot identify the approach path. Both systems are referenced in the FAA's inoperative components table, which specifies the increase in approach minimums required when these lights are not working.
Plain English
Two versions of a shorter approach light system that sits just before the runway. SALS is a line of steady white lights that points the pilot to the runway. SALSF is the same line of lights plus a chain of flashing lights that pulse toward the runway one after another, like a moving arrow guiding you in.
Context Anchor
Seen on instrument approach charts and in inoperative component tables when checking what runway lights are available or out of service for an approach.
Derivation
The names are simply built from their function: 'Short' because the lighting array is shorter than the longer ALSF systems; 'Approach Lighting System' because the lights guide the aircraft on the final approach; and 'Sequenced Flashing' in SALSF because the added lights flash one after another in sequence.
Why Pilots Care
An inoperative SALS or SALSF raises the published visibility or ceiling required to continue the approach, which can prevent landing.
Grounding Statement
On final approach in low visibility, SALS/SALSF gives the pilot a lighted path leading to the runway end.
Intuition Check
Do not treat SALS/SALSF as ordinary runway edge lighting. It is an approach lighting system placed before the runway to help you find and align with the runway during the last part of the approach.
Example Sentence 1
The approach chart noted that the runway was equipped with SALSF, so the pilot expected to see the sequenced flashing lights leading to the threshold as she broke out of the clouds.
Example Sentence 2
With SALSF inoperative the approach required an extra quarter mile of visibility.