How do planes dump fuel?

Answers to your questions about the news.
Sept. 22 2005 6:38 PM

How Do You Dump Fuel From a Plane?

Just turn on your fuel dumping system.

Planes must lighten their load to land. 
Click image to expand.
Planes must lighten their load to land

A plane operated by JetBlue made an emergency landing in Los Angeles Wednesday night, after air-traffic controllers noticed that its landing gear was twisted to the side. The pilots first circled for three hours, to burn off fuel and lighten the aircraft. If they'd been flying a different kind of plane, they might have been able to dump the fuel instead. How do planes dump fuel?

Daniel Engber Daniel Engber

Daniel Engber is a columnist for Slate

It's as easy as flipping a switch. Many commercial airplanes (and almost all military aircraft) have a built-in fuel-dumping system that uses pumps and valves to release fuel from the wings and sometimes the tail. These systems, controlled from the cockpit, typically allow a plane to eject several thousand pounds of fuel per minute; a standard fuel-dumping operation could take around 10 minutes to complete.

Advertisement

Why would you need to dump fuel? A plane that lands too heavy risks structural damage (particularly to its landing gear), so manufacturers assign each model a maximum landing weight based on the sturdiness of its parts. Since planes burn fuel and get lighter as they fly, most are designed to carry much less weight at landing than take-off. A 747 that's fully gassed up for a long trip might burn through hundreds of thousands of pounds of jet fuel before it landed.

If the 747 were forced to land well ahead of schedule, it would be far too heavy for a safe touchdown. An overweight plane probably won't break apart when it hits the ground, but it may become unsafe for future flights. Airline mechanics would have to give it a thorough inspection, perhaps even dismantling parts of the plane, before allowing it to fly again. These hassles can be avoided, though, if the pilot just flips on the dumping system.

Dumped fuel flows out behind the plane like a contrail, and then most of it evaporates before it reaches the ground. Exactly how much of the fuel plume evaporates depends on several factors, including altitude, air temperature, and dumping pressure. In general, at least half of the fuel—and sometimes more than 99 percent of it—will dissipate. Fuel dumped from a high altitude in warm weather disperses best.

The Federal Aviation Administration's dumping policy prescribes a minimum altitude for dumping, and a five-mile separation from other aircraft. Air traffic controllers try to direct dumping planes away from populated areas and toward large bodies of water. (Experts guess that more than 15 million pounds of jettisoned fuel rained down into the oceans from civilian and military aircraft during the 1990s.)

Explainer thanks Al Dickinson of the University of Southern California and Cass Howell of Embry-Riddle Aeronautical University.

TODAY IN SLATE

Politics

Smash and Grab

Will competitive Senate contests in Kansas and South Dakota lead to more late-breaking races in future elections?

Stop Panicking. America Is Now in Very Good Shape to Respond to the Ebola Crisis.

The 2014 Kansas City Royals Show the Value of Building a Mediocre Baseball Team

The GOP Won’t Win Any Black Votes With Its New “Willie Horton” Ad

Sleater-Kinney Was Once America’s Best Rock Band

Can it be again?

Technocracy

Forget Oculus Rift

This $25 cardboard box turns your phone into an incredibly fun virtual reality experience.

One of Putin’s Favorite Oligarchs Wants to Start an Orthodox Christian Fox News

These Companies in Japan Are More Than 1,000 Years Old

Trending News Channel
Oct. 20 2014 6:17 PM Watch Flashes of Lightning Created in a Lab  
  News & Politics
Politics
Oct. 20 2014 8:14 PM You Should Be Optimistic About Ebola Don’t panic. Here are all the signs that the U.S. is containing the disease.
  Business
Moneybox
Oct. 20 2014 7:23 PM Chipotle’s Magical Burrito Empire Keeps Growing, Might Be Slowing
  Life
Dear Prudence
Oct. 21 2014 9:18 AM Oh, Boy Prudie counsels a letter writer whose sister dresses her 4-year-old son in pink tutus.
  Double X
The XX Factor
Oct. 20 2014 6:17 PM I Am 25. I Don't Work at Facebook. My Doctors Want Me to Freeze My Eggs.
  Slate Plus
Tv Club
Oct. 20 2014 7:15 AM The Slate Doctor Who Podcast: Episode 9 A spoiler-filled discussion of "Flatline."
  Arts
Brow Beat
Oct. 21 2014 10:10 AM Where Do I Start With Sleater-Kinney?
  Technology
Future Tense
Oct. 21 2014 9:39 AM The International-Student Revolving Door Foreign students shouldn’t have to prove they’ll go home after graduating to get a visa.
  Health & Science
Bad Astronomy
Oct. 21 2014 7:00 AM Watch the Moon Eat the Sun: The Partial Solar Eclipse on Thursday, Oct. 23
  Sports
Sports Nut
Oct. 20 2014 5:09 PM Keepaway, on Three. Ready—Break! On his record-breaking touchdown pass, Peyton Manning couldn’t even leave the celebration to chance.