Highest altitude mid-air collision

The highest altitude at which two aircraft are known to have collided is 11,582 m (38,000 ft). The incident occurred in the early hours of 5 February 1958, when a US Air Force B-47 bomber collided with a F-86 fighter on a training flight over Georgia, USA.

Mid-air collisions typically occur at low altitudes in the congested airspace around airports, so collisions such as this one – involving two aircraft at cruising altitude – extremely rare.

The B-47, from the 19th Bombardment Wing, was taking part in an exercise known as a Unit Simulated Combat Mission. It had left its base in Florida the previous day, and was now returning from a practice bombing run on the town of Radford, Virginia. To make sure the training exercise was as realistic as possible, the aircraft was carrying a real Mk-15 thermonuclear bomb (minus its plutonium detonator core).

At around 00:30, the crew of the B-47 – which comprised Howard Richardson (commander), Robert Lagerstrom (co-pilot) and Leland Woolard (navigator) – heard a loud bang and the whole plane began to shake violently. They looked across to their starboard wing and saw that the wing-mounted fuel tank had been ripped away; the control surfaces were partially destroyed, and the outboard engine was bent upwards, held on by only a few shreds of bodywork.

Unknown to them, an F-86 Sabre from the 444th Fighter-Interceptor Squadron – also on a training mission – had crashed into their wing in the darkness. This was a vanishingly unlikely event considering that the two aircraft were on different missions, and flying out of different air bases hundreds of miles apart.

The F-86's pilot, Clarence Stewart, ejected safely from his disintegrating aircraft, but his parachute opened early, forcing him to endure a long slow descent through the frigid upper atmosphere. He landed in the middle of a swamp in South Carolina with frostbitten hands, but survived to fly again.

After a rapid descent to around 6,000 m (20,000 ft), Richardson and his crew managed to regain control of the aircraft. They were now faced with the prospect of a hard landing with a 3,450 kg (7,600 lb) nuclear bomb mounted directly behind the cockpit. Concerned that it would break free and crush the crew compartment on landing, Richardson requested permission to ditch the bomb.

With permission granted, the crew jettisoned the bomb and watched it splash down with no explosion just off the coast of Tybee Island, Georgia. They then swung the damaged plane around for an emergency landing at Hunter Air Force base in nearby Savannah.

The crew all survived, and Howard Richardson was awarded the Distinguished Flying Cross for his actions, but efforts to recover the bomb were not successful. In April 1958, Navy divers declared it "irretrievably lost". To this day, the incomplete hydrogen bomb, which contains a large quantity of conventional high explosives and a even larger quantity of weapons-grade uranium, remains hidden in the silt of the Wassaw Sound, around 20 km (12.4 mi) from the city of Savannah, Georgia.