1948 Northwood mid-air collision

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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 (then in Middlesex). 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.

The DC-6, registration SE-BDA and named Agnar Viking, was on an international scheduled flight from Stockholm via Amsterdam to London's RAF Northolt. The Avro York of the 99 Squadron, with serial number MW248, was on a flight from RAF Luqa in Malta to RAF Northolt. The aircraft were two of four participating in a stacking at Northolt. At the time of the accident, the SAS aircraft was holding at 2,500 feet while the RAF aircraft was holding at 3,000 feet. However, due to an error in the setting of the atmospheric pressure compensation of the RAF aircraft, it may have been lower. At the time of the collision the DC-6 was ascending, as the pilots had minutes before having to decide to leave the stacking and divert to Amsterdam.