page_title: 1948 Northwood mid-air collision
section_title: Collision
hierarchical_section_title: 1948 Northwood mid-air collision / Collision
caption_attribution_description: English: Scandinavian Airways (SAS) taking off from Heathrow in 1955. Back in 1955, you watched from Queen's Building this kind of piston-engined aircraft. This is a Douglas DC-6, employed by SAS in the late 1950s.
context_page_description: The 1948 Northwood mid-air collision took place on 4 July at 15:03 when a Douglas DC-6 of Scandinavian Airlines System and an Avro York C.1 of the Royal Air Force 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.
  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 Norholt. 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 decided to divert to Amsterdam and to leave the stacking.
context_section_description: Upon arrival in the Northolt area both aircraft were placed in a stacking pattern, which in addition to the two involved aircraft included two other aircraft at higher altitudes. Each stack had an intermediate distance of 500 feet. The stacking was regulated by the air traffic control of Metropolitan Zone. Any aircraft entering the stack had to follow orders from air traffic control, which indicated their altitudes and route, and issued gates allowing the aircraft to enter and leave. Air traffic control issued atmospheric pressure measurements (QFE), allowing the aircraft to synchronise their altimeters.
  At 14:12, the York was given permission to enter the Metropolitan Zone at 5,000 feet over Woodley, near Reading. It was at 14:38 told to circle Northolt at 5,000 feet. Air traffic control then gave the Swedish aircraft permission at 14:45 to descend to 2,500 feet. The RAF aircraft was cleared at 14:50 to descend to 4,000 feet. At 14:52 the DC-6 reported "just passed 2,500 feet; going down". The controller reminded the pilot that he was only cleared to 2,500 feet and was not to descend.
  Three minutes after the DC-6 report at 2,500 feet, at 14:54, the York was cleared down to 3,000 feet. The DC-6 decided to divert to Amsterdam at 14:59 and informed the tower; it was cleared to leave the area at 2,500 feet at 15:03 although this was not acknowledged by the DC-6. Nothing was heard from the York after 14:45 and it did not acknowledge further clearance down to 1,500 ft at 15:05.
  The permission for the York to descend was given at least a minute or two after the DC-6 was cleared from the area, but neither aircraft acknowledged the last messages. At 15:03 the two aircraft collided about 6.4 kilometres (3.5 nmi; 4.0 mi) north of Northolt Aerodrome. An investigation officer from the Ministry of Civil Aviation later reported that the York was above the DC-6, which was climbing. The starboard wing of the DC-6 penetrated the York on the starboard side behind the freight door and detached the York's tail unit.
  Both aircraft crashed into a wood, bursting into flames on impact. After fire and rescue crews put out the fires, the Avro York was found to be completely destroyed by the crash and the only part of the DC-6 that was still intact was the rudder and tailplane, with the rest of the DC-6 also being destroyed by the fire. All seven passengers and crew of the Avro York died and all thirty-two passengers and crew of the DC-6 also died, bringing the total number of deaths to thirty-nine.
  The collision was at the time the most lethal aviation accident in the United Kingdom and is still the most fatal mid-air collision. It now ranks as the fifteenth-most fatal accident in Britain. The accident was SAS's first fatal accident. It was the fourth loss of a DC-6 and the third-most fatal at the time.
caption: A SAS Douglas DC-6 similar to the one in the collision
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