British Airways Flight 9 is the main reason why all flights were cancelled in Europe

British Airways Flight 9, sometimes referred to as the Speedbird 9 or Jakarta incident, was a scheduled British Airways flight from London Heathrow to Auckland, with stops in Bombay, Madras, Kuala Lumpur, Perth and Melbourne.
On 24 June 1982, the route was flown by a 747-236B registered G-BDXH. The aircraft flew into a cloud of volcanic ash thrown up by the eruption of Mount Galunggung (c. 180 km south-east of Jakarta, Indonesia), resulting in the failure of all four engines. The reason for the failure was not immediately apparent to the crew or ground control. The aircraft was diverted to Jakarta in the hope that enough engines could be restarted to allow it to land there. The aircraft was able to glide far enough to exit the ash cloud, and all engines were restarted (although one failed again soon after) allowing the aircraft to land safely.
248 pax and 15 crew lived to tell the tale. This is the [link] for the rest of the story.