Definition
A medium-intensity approach lighting system installed on the extended runway centerline before the threshold, consisting of steady-burning white light bars and a row of sequenced flashing lights that fire in rapid succession from the outermost light toward the runway. The sequenced flashers create a visible 'rabbit' of light running toward the threshold, helping the pilot identify the approach path and align the aircraft during the transition from instrument to visual flight.
Plain English
A line of approach lights leading up to the runway, with some of the lights flashing one after another in a fast pulse that points toward the runway. It is dimmer than the brightest systems and is used at runways where extra help picking out the approach path is needed.
Context Anchor
Seen on instrument approach charts and during the final part of an approach to a runway served by this lighting system.
Derivation
The name describes the system directly: 'medium intensity' refers to the brightness category (between basic and high-intensity systems), and 'sequenced flashing lights' refers to the rapid one-after-the-other firing pattern. The pilot community nickname 'the rabbit' comes from the way the flash appears to run along the ground toward the runway.
Why Pilots Care
Gives pilots a reliable visual reference to the runway threshold in low visibility or at night, reducing the chance of misalignment during landing.
Intuition Check
“Medium intensity” does not mean the system is less important. It describes the brightness category of the lights, not the operational value of the system.
Example Sentence 1
Breaking out of the clouds at minimums, the pilot identified the MALSF and continued the approach to landing.
Example Sentence 2
Many non-towered airports use MALSF because it offers good guidance without the higher cost of a full high-intensity system.