An Air France Boeing 777 obliged to dump some of its fuel above the famous forest of Fontainebleau on the outskirts of Paris. This story made the headlines on 25th September. Yet this unusual procedure is in fact a classic solution to aircraft experiencing technical problems.
The fuel is dumped via drainage taps situated at the end of each of the wing, enabling them to get rid of roughly a tonne of fuel per minute. And while it’s the pilots that decide the quantity of fuel to jettison, it’s air control, which authorises it to be carried out.
The minimal altitude for fuel dumping is usually around 6,000 feet (1,800 metres), considered by air authorities to be the altitude allowing 90% of the kerosene to be evaporated before touching the ground. Thus allowing a minimal impact on the environment.
This system of kerosene dumping, which only exists on long-haul planes, is proposed as an option for air companies. If the apparatus is not suited to this, there exists – as a last resort - an emergency “heavy landing” procedure.