1991 Los Angeles runway collision

On the evening of Friday, February 1, 1991, USAir Flight 1493, a Boeing 737-300, collided with SkyWest Airlines Flight 5569, a Fairchild Swearingen Metroliner turboprop aircraft, upon landing at Los Angeles International Airport (LAX). As Flight 1493 was on final approach, the local controller was distracted, though air traffic was not heavy at LAX, by a series of abnormalities, including a misplaced flight progress strip and an aircraft that had inadvertently switched off the tower frequency.

Source: Wikipedia — 1991 Los Angeles runway collision (CC BY-SA 4.0)