Dutch investigators have disclosed that a Boeing 777-200 operated by KLM nearly struck a weather balloon during high-altitude climb out of Amsterdam.
The twinjet (PH-BQL) had been operating a transatlantic service to Atlanta and had been passing over the North Sea when the incident occurred.
In a brief bulletin the Dutch Safety Board states that the 777 had been climbing through 15,000ft when it encountered the balloon.
It states that the pilots estimated the horizontal separation to be 8m (26ft) and the vertical separation to be just 1m.
There were no injuries among the 286 passengers on board. The event occurred on 16 February this year, at around 17:15.
In its bulletin the Dutch Safety Board has classified the incident as "serious" but says the service continued without further interruption. It has not given the source of the balloon.