The German Flight Safety Authority reported the incident on Thursday.
The Cargolux 747-4R7F, en route to Johannesburg, climbed to a height of around 5 kilometres before dumping the fuel, which — at this altitude — evaporates in the atmosphere.
Airplanes release kerosene in emergencies to reduce weight before landing.
It is unclear what led to issues with the engine which necessitated the offloading.
