When you develop a STANDARD that means whatever the heck it is happens a lot. Why is dumping fuel IN AN EMERGENCY so frequent?

You are thinking of that fuel that showered a school playground full of children? (It was reported on the BBC News.)

It is not worth the risk of taking off with any less than full tanks. You can't assume that because a certain aeroplane uses a certain number of gallons of fuel for a regular flight week after week, it will always need only that.

The fuel consumption for flying a particular plane and its load purely by distance is known, but the flight itself may be against headwinds that have the effect of increasing the distance, or tail-winds that have the reverse effect. Weather or other problems may enforce a long holding pattern or even a detour, possibly of a few hundred miles. So no taking chances with only part-filled tanks. 

So if the aircraft approaches its destination still with plenty of fuel on board the pilot may decide for safety reasons to drain a lot of that off. If nothing else it lessens the landing weight. Now, they are supposed to dump fuel in designated areas well away from anywhere like homes and schools; so something went wrong in the Californian case; but as far I understood it the aircraft was not in some emergency situation.

Obviously it is not for us to speculate why the fuel was jettisoned where it was, but one question I would ask if investigating the incident, would be if someone miscalculated the wind speed and direction so the spray was blown across an urban area. 


[ One of the earliest so-called 'Bermuda Triangle' disappearances, in the 1930s I think, highlighted the headwind problem. An airliner flying from Britain to the Southern USA vanished over the ocean. Investigations revealed it was owned by a small airline not too thorough with maintenance; the plane should have been refuelled in the Azores but was not; and meteorological records showed it would have met strong headwinds over the Western Atlantic.  It almost certainly simply ran out of fuel and fell into the sea, taking all on board with it. ]