TCAS, the Traffic Collision Avoidance System fitted to commercial aircraft, monitors nearby transponder equipped traffic and issues resolution advisories when a collision risk develops. Increase climb is one of those advisories, telling the crew to climb at a greater vertical speed than first instructed. Recordings and simulator recreations of the voice have circulated among aviation enthusiasts, flight simulation communities and cockpit video editors. Online, the clip survives because the phrasing is so specific and authoritative that viewers recognise an in-flight emergency even without seeing an aircraft.