The Boeing 717 is a twin-engine, single-aisle jet airliner originally developed by McDonnell Douglas as the MD-95 and renamed after its merger with Boeing in 1997. The type entered service in 1999 and was built until 2006. Its cockpit altitude alerting system sounds a chime as the jet nears the altitude selected by the crew, a standard safety prompt in modern airliners. Flight simulator and aviation enthusiasts later isolated the short warning tone, sharing it online for realistic cockpit edits, training videos and aviation-themed memes.