Definition
A standard approach lighting system installed at the approach end of an instrument runway, consisting of a row of medium-intensity steady white lights extending outward from the runway threshold along the extended runway centerline, combined with a set of sequenced flashing lights (the Runway Alignment Indicator Lights, or RAIL) that pulse toward the runway. MALSR provides visual guidance to pilots transitioning from instrument flight to visual references during the final stages of an instrument approach.
Plain English
A line of bright white lights leading up to the runway, with extra flashing lights that appear to chase toward the runway. They help a pilot find and line up with the runway when breaking out of cloud near the end of an approach.
Context Anchor
Seen on instrument approach procedure charts and airport information when a runway has this type of approach lighting installed.
Derivation
The name describes the system itself: 'Medium Intensity' refers to the brightness level (between low and high intensity systems), 'Approach Lighting System' is the row of lights leading to the runway, and 'Runway Alignment Indicator Lights' are the sequenced flashers that visually point toward the runway. Knowing the parts of the name tells you exactly what you're looking at out the window.
Why Pilots Care
Allows a pilot to transition from instruments to a stabilized visual landing in marginal weather, reducing the risk of misalignment or controlled flight into terrain.
Grounding Statement
On final approach in haze or low clouds, MALSR gives a lighted path pointing toward the landing runway.
Intuition Check
MALSR is not the instrument approach procedure itself. It is the lighting system near the runway that helps you see and align with the runway at the end of the approach.
Example Sentence 1
The approach plate showed a MALSR serving Runway 27, so the crew briefed that they would look for the sequenced flashers and white centerline lights as they approached minimums.
Example Sentence 2
After breaking out at minimums, the pilot used the MALSR lights to confirm runway alignment before landing.