Butter has long been flight simulator slang for an exceptionally smooth landing, where the aircraft touches down softly with minimal bounce. Swiss001, a Swiss flight simulation creator, helped popularise the term through landing challenges and attempts at demanding airports. London City is a favourite test because its steep approach and short runway leave little room for error, especially in a larger jet like the Airbus A320. Clips labelled Swiss001 butter are now shared among aviation and simulator fans as shorthand for nailing a difficult touchdown cleanly.