Callsign RUK is Ryanair UK
WHAT AIRLINE IS RUK?
RUK is the ICAO three-letter callsign prefix for Ryanair UK. When a radio scanner, flight tracker or radar scope shows a flight like RUK123 or RUK45XY overhead, that's a Ryanair UK aircraft talking to air traffic control.
Spot one yourself: open the live scope, enter your postcode, and tap any blip whose callsign starts with RUK for its type, registration, route and photo.