Plain English Meaning

A row of approach lights leading up to the runway, set at medium brightness, with flashing lights at the far end that pulse one after another in a wave pointing toward the runway. The wave of flashes shows the pilot which way the runway is and helps them line up with it as they break out of the clouds.

Full Definition

A medium-intensity approach lighting system installed at the approach end of a runway, consisting of steady-burning white light bars extending outward from the runway threshold along the extended centerline, plus a series of sequenced flashing lights in the outer portion that fire one after another toward the runway. The sequenced flashers create a visible 'ball of light' that appears to travel down the lighting array toward the , helping the pilot align with and the runway during an .