Definition
A medium-intensity approach lighting system installed at the approach end of a runway, consisting of a row of steady white lights extending outward from the threshold along the extended runway centerline, with sequenced flashing lights added in the outer portion. The flashers fire in rapid succession from the far end toward the runway, producing a visible 'ball of light' that travels toward the threshold to guide pilots to the runway during instrument approaches in reduced visibility.
Plain English
A line of approach lights at the start of a runway, set at medium brightness, with some lights that flash one after another in a running pattern pointing toward the runway. The running flash helps the pilot find the runway when visibility is poor.
Context Anchor
You may see MALSF listed on instrument approach charts, airport lighting information, or airport notices about runway light systems being out of service.
Why Pilots Care
Provides reliable visual cues for runway alignment and threshold location, especially at night or in marginal visibility.
Grounding Statement
Picture a line of lights stretching out from the runway end, with flashes running toward the runway to draw your eyes in the right direction.
Intuition Check
“Medium intensity” means a brightness category, not that the system is of medium importance. “Sequenced flashers” means the flashing lights fire in order toward the runway, not randomly.
Example Sentence 1
The approach plate showed MALSF serving Runway 27, so the crew briefed the sequenced flashers as their primary cue for acquiring the runway environment.
Example Sentence 2
ATC reported the MALSF was operational, giving the arriving aircraft clear visual guidance to the threshold.