Definition
A medium-intensity approach lighting system installed at the approach end of a runway, consisting of a centerline of steady-burning white lights extending outward from the runway threshold, plus a sequence of flashing lights (the Runway Alignment Indicator Lights, or RAIL) that pulse in sequence toward the runway. MALSR is a standard FAA approach light configuration used to help pilots transition from instrument flight to visual references during the final stages of an instrument approach, and its presence affects the visibility minimums published for the approach.
Plain English
A line of lights leading up to the start of a runway. Some of the lights are steady; others flash one after another, pointing the way to the runway. They help pilots see and line up with the runway when breaking out of cloud or low visibility.
Context Anchor
Seen on instrument approach charts, airport information, and operations specifications when a procedure or authorization depends on the runway lighting available.
Derivation
‘Approach lighting’ describes the function — lights that guide you on approach. ‘Medium intensity’ distinguishes it from higher-powered systems used at busier or lower-minimums runways. The ‘R’ stands for Runway Alignment Indicator Lights, the sequenced flashing portion that visually pulls the eye toward the runway.
Why Pilots Care
Allows pilots to transition from instrument to visual flight safely during approach in marginal weather conditions.
Intuition Check
Do not read “medium intensity” as a casual description meaning “somewhat bright.” In this term, it is the FAA name for a specific type of approach lighting system, and the “R” refers to runway alignment indicator lights.
Example Sentence 1
After breaking out of the clouds at minimums, the pilot identified the sequenced flashers of the MALSR and continued the approach to landing.
Example Sentence 2
Helicopter operations specifications often require MALSR availability for certain instrument procedures at night.