What happened
On the morning of 5 March 1966, British Overseas Airways Corporation (BOAC) Flight 911 departed from Tokyo Haneda Airport. The aircraft, a Boeing 707-436 with registration G-APFG, was operating a segment of its round-the-world service destined for London Heathrow via Hong Kong and Karachi.
Shortly after lifting off, the jet encountered severe clear-air turbulence while climbing through the airspace near Mount Fuji. The atmospheric disturbance caused the aircraft to break apart mid-flight. There were no distress signals received from the cockpit, and the wreckage was scattered across a wide area in the mountains. All 124 individuals on board—comprising 113 passengers and 11 crew members—perished in the incident.
Investigation
Japanese authorities conducted an extensive search and recovery operation to locate debris from the flight. The investigation focused heavily on determining why a modern jetliner would fail structurally without warning. Investigators examined weather reports for the region, noting that while no thunderstorms were present, strong upper-level winds were recorded at the altitude of the accident.
The lack of radar echoes and the absence of storm activity led investigators to conclude that the aircraft had struck clear-air turbulence. This type of turbulence is invisible to standard meteorological radar and difficult for pilots to detect visually until it is encountered.
Findings
The official inquiry determined that the primary factor was the encounter with severe clear-air turbulence. The structural loads generated by the sudden atmospheric forces exceeded the design limits of the airframe, leading to immediate catastrophic failure. This tragedy highlighted the dangers of high-altitude wind shear and contributed to later advancements in turbulence detection and reporting protocols.