The Reason Why Fuel Dumped From an Airplane Doesn't Reach the Ground

Here’s a little-known fact about airplanes. To land safely, they typically need to be lighter upon landing than they were during take-off. That’s easy enough to accomplish, since they burn hundreds of thousands of gallons of fuel during flights.

In emergency situations, however, it’s possible that a pilot will need to plan an urgent landing, at which point fuel jettisoning becomes a priority. Thousands of gallons will be discarded—yet we never hear of towns being deluged by a storm of airplane fuel. Here’s why.

When an airplane is high up in the atmosphere—typically at 5000 feet or above—discarded fuel will simply evaporate. Pilots who eject fuel use caution to make sure no aircraft is nearby to be caught in the fuel shower, and systems are in place to prevent them from draining all their fuel (as that would obviously create a different set of problems). Some planes have systems to spray fuel from nozzles located on the wings and can dump thousands of pounds of fuel per second.

Of course, just because liquid fuel doesn’t begin raining over a population doesn’t mean it disappears entirely. Some fuel will remain suspended in the atmosphere, and some of the vapor will wind up sinking to the ground. Picked up by wind, it might even wind up contributing to smog.

Dumping fuel is a rare event reserved for when pilots need to make a prompt landing owing to medical or maintenance issues but don’t want excess weight straining the aircraft. If there’s time, they can fly around to burn fuel, dropping the gear or flaps to help use more of it. But if discarding fuel is the only option, you can rest assured it won’t be staining your clothes.

[h/t HowStuffWorks]