The 1948 Northwood mid-air collision took place on 4 July at 15:03 when a Douglas DC-6 of Scandinavian Airlines System (SAS) and an Avro York C.1 of the Royal Air Force (RAF) collided in mid-air over Northwood in London, UK. All thirty-nine people aboard both aircraft were killed. It was SAS's first fatal aviation accident and was at the time the deadliest civilian aviation accident in the UK. It is still the deadliest mid-air collision in British history.