The MALSR is a medium-intensity approach lighting system (ALS) installed in airport runway approach zones along the extended centerline of the runway. MALSRs consist of a combination of steady burning light bars and flashers that provide pilot's visual information on runway alignment, height perception, roll guidance, and horizontal references to support the visual portion of an instrument approach.
The MALSR system consists of a Threshold Light, Steady Burning Light, and Sequenced Flasher. The threshold light array consists of 18 to 33 aviation green steady burning lights depending on runway width, arranged in a line at and parallel to the threshold of the runway. The steady burning light array consists of nine (9) sets of five (5) aviation white steady burning light sources called light bars. Seven (7) of the light bars are located at 200-foot intervals, in the direction of the approach and along the extended runway centerline, starting beyond the runway threshold. The remaining two steady burning light bars are offset to the left and right of the extended centerline at the 1,000-foot bar. The threshold light array and steady burning light array are collectively referred to as the approach light field. The sequenced flasher array consists of five (5) white flashing lamps, commonly referred to as flashers. The flasher are located at 200-foot intervals, in the direction of the approach and along the extended runway centerline, starting at 200 feet beyond the last steady burning light bar beginning at 1600 feet from the runway threshold. The collective flashing of all lights in the sequenced flasher array gives the appearance of a ball of light traveling toward the runway.