Swissair flight 306 was depart Zurich for Geneva at 7am the morning of September 4, 1963. In command of the Sud Aviation Caravelle that morning was Captain Eugene Holhi and First Officer Rudolph Widmel. Along with three flight attendants, there were 74 passengers on board that morning. Weather was good in the area, but morning fog was lying in the valley areas and the airport was still closed when 306's departure time came. Holhi asked the tower controller for permission to taxi out onto the runway so he could take a look at the visibility available. A guide vehicle led the aircraft to the runway and Holhli taxied the Caravelle about 4,000ft down the runway with the engines at high power. He then turned around and taxied back to the start of the runway.


Radioing the tower, he reported that the visibility varied along the runway and that the jet exhaust had blown away some of the fog. Holhli then asked for permission to take off and it was promptly granted. Shortly afterwards, 306 reported being in clear conditions above the fog and climbing through 1,700ft. The flight was then handed off to Zurich departure. Only a few minutes afterwards, the crew made a Mayday call, which was to be the last transmission from the aircraft. A farmer working on the mountainside saw the Caravelle in flight, trailing smoke from it's port side followed shortly by an outbreak of flames. The aircraft then began a left-turning descent, plunging back into the fog. Another person on the ground below the fog reported seeing the aircraft emerge from the fog in a steep dive, flames pouring out of the left side of the aircraft just before it impacted the ground on the outskirts of a local village. Wreckage was scattered around the impact site, damaging homes and setting structures on fire. No survivors were found.

Investigators were able to locate the FDR, but it provided no clues as to the cause of the accident. The only information they had to go on was the eyewitness reports of fire on the left side of the aircraft. Investigators found pieces of the aircraft's left side undercarriage, port wing, and rear fuselage along the last six miles of the aircraft's flight path. Back at the airport, investigators found part of the outer rim of the left inside wheel. Near this, there was blow-out stain and an earthing cable.

Along the wheel tracks after this stain were traces of hydraulic oil and and pieces of the inner port wheel. Investigators determined that excessive breaking had to be used to keep the aircraft slowed down while high engine power was used during taxiing. This excessive braking caused extremely high temperatures which led to the fracture of the outer rim. They further determined that this excessive heating could have ignited the then leaking hydraulic fluid. Further, once the gear was retracted after takeoff, the excessive heat could have further damaged fuel lines and other critical components in the undercarriage area, igniting the subsequent fire. In flight, this fire caused a weakening of the structural support of the wing and a loss of hydraulic fluid to the control systems.