From CNN:

Officials from the Adolfo Suárez-Madrid Barajas airport are trying to find the owners of a plane that has been parked on the tarmac, without moving, for years.
Airport director Elena Mayoral submitted an official notice to the Boletín Oficial del Estado, the official gazette of the Kingdom of Spain, informing the nation of a plane in an “obvious state of abandonment” at the airport.

Once the official notice goes out, the owner has three months to get in touch with the airport otherwise the plane will be sold off at auction.