Water cannon salutes are celebratory gestures typically deployed for special flights, such as the inaugural or final service on a given route. Occasionally, these will also be used to mark a pilot’s retirement. Spraying aircraft in such a manner is harmless, as long, that is, as water is what is sprayed. In 2015, a mixup at the UK’s Manchester Airport caused a Virgin Atlantic Airbus A330 to be sprayed with foam instead.