According to the Swiss news service ATS, a Corsair Boeing B747 flying from Paris to Mauritius on Sunday, dropped 70 tonnes of fuel in Swiss and Italian airspace.
The aircraft, bound for Mauritius, had technical problems and had to return to Paris to land.
Certain aircraft, such as the Boeing B747, have a maximum landing weight lower than their maximum take off weight. At the start of long haul trips requiring lots of fuel, maximum landing weight is often exceeded. Landing unexpectedly early on in a long flight requires fuel dumping to reach a safe landing weight.
The Mauritius bound Corsair flight needed to make a u-turn back to Paris while flying over northern Italy. On its return it dropped 70 tonnes of fuel over the Alps in Italian and Swiss airspace at altitudes between 6,700 and 9,400 metres.
Fuel dumped at high altitude dissipates before reaching the ground. The photograph below shows fuel being dumped from an A340-600 over the Atlantic.
According to Skyguide, the Geneva-based air traffic control company, the Corsair aircraft successfully landed in Paris.