A significant and recurring operational criticism of Sofia Airport has concerned its historical lack of all-weather operations capability. Though the new runway was designed for ICAO Category 3 operations, in 2007 it emerged that radio interference from security fencing, and most significantly from a large newly built lorry park, prevented certification (and hence use) of the associated radio navigational aids. During the winter months, the airport, located on a high alluvial plain surrounded by mountains, suffers from very significant and frequent fog precipitation. In such circumstances, flights are redirected to diversion airports in Bulgaria or neighbouring countries, lengthening journeys by many hours.