The one hundred callout comes from the radio altitude announcements used in Boeing commercial aircraft, where the ground proximity warning system reads out height above terrain during approach and landing. The voice is a standard cockpit alert, designed to be unmistakable and calm under pressure, and it has become familiar to anyone who watches cockpit videos or flies in simulators. Aviation creators reuse it because it instantly places a scene in a real airliner cockpit, without needing narration to explain how close the aircraft is to the runway.