The sound comes from real Airbus aircraft rather than a film or television show, and it is produced by the hydraulic power transfer unit that balances pressure between systems while the aircraft is on the ground. Plane spotters and aviation enthusiasts began sharing recordings of the distinctive bark because it sounds so unlike a normal machine noise, and clips soon circulated in travel videos, aviation explainers and short-form posts. It remains popular because it is instantly recognisable to frequent flyers, easy to drop into a joke, and a quick shorthand for anything related to flying.