The main reason planes dump fuel is to reduce their weight, which is especially important when it comes to landing safely.

Airplanes have a safe landing weight, the same way they have a safe takeoff weight. Landing above this weight may result in structural damage when landing, which would put everyone on the plane in danger.

Airplanes also commonly dump fuel before emergency landings because they need to rapidly reduce their weight before landing.

Jettisoning airplane fuel is effective since airplane fuel is heavy, weighing up to 6 pounds per gallon.

Airplanes jettison fuel using a system of pumps and valves that release the fuel from the plane’s wingtips.

The ejected fuel then evaporates in the air and doesn’t reach the ground, so it has a negligible environmental impact. 

Why Planes Dump Fuel Before Landing

Planes dump fuel before landing to lower the plane’s weight.

Lowering the plane’s weight decreases the stress with which the plane lands, making the landing safer.

Planes only dump fuel immediately before they’re about to land.

Airplane fuel weighs as much as 6 pounds per gallon. So, a plane that holds 5,000 gallons of fuel carries up to 30,000lbs of extra weight. 

Why Planes Dump Fuel Before an Emergency Landing

Planes dump fuel before an emergency landing to quickly achieve the safe weight needed to land the plane without suffering from structural damage.

Normally, a plane achieves this safe weight by reducing its weight immediately before landing, but, during an emergency, the plane may not have been in the air long enough to burn enough fuel.

As a result, the plane would have too much weight to safely land.

So, the flight crew has to quickly remove the excess weight by dumping the fuel before the plane makes an emergency landing.

How Planes Dump Fuel

Planes have fuel jettisoning systems that can dump thousands of pounds of fuel per second.

The pilot activates the jettisoning fuel system via controls in the cockpit.

The fuel jettisoning system usually consists of a set of pumps and valves that divert fuel to the tip of the wing’s planes. 

The fuel then streams from the plane’s wingtips like a contrail.

The pilot also has failsafe systems that prevent jettisoning all the fuel at once.

These fuel jettisoning systems usually also have precise measurements about how much fuel has been released and how much remains, so pilots easily monitor their fuel situation. 

Not all planes can dump fuel. though.

Most large planes, like the Boeing 747 and Airbus A380, can, but smaller planes either land overweight or carry less fuel. 

Planes Will Rarely Dump Fuel

Commercial airplanes rarely dump fuel in large amounts.

Most of the time, they dump fuel only during emergencies.

Airplanes also dump fuel immediately before landing if their overall weight exceeds the safe landing weight.

A Plane Can Still Land When it’s Overweight

The alternative to dumping fuel is to land the plane while it’s overweight.

The FAA consider both landing overweight and jettisoning fuel as safe procedures, but, it’s dangerous to land an overweight plane with an engine failure or other technical issues. 

That being said, it could also be dangerous to delay landing a plane with an engine failure or other technical issues, to reduce the plane’s weight.

So, most pilots choose to land the aircraft overweight instead of dumping fuel. 

Negligible Environmental Impact From Fuel Dumping

The environmental impact of airplanes dumping fuel is negligible, as most aircraft fuel is highly volatile and quickly evaporates.

Pilots also only dump fuel when the plane reaches a high enough altitude.

An IPPC report states that even the occasional introduction of hydrocarbons in the environment by jettisoning fuel at lower altitudes has a negligible effect on the atmosphere. 

Theoretically, the liquid fuel would cause environmental damage if it reached the ground.

Routine dumping of aircraft fuel on water resources would cause environmental degradation, water pollution, and crop damage. 

Jet fuel contains different hydrocarbons, including benzene, which harms the environment and causes cancer.

Benzene exposure would decay plants and contaminate groundwater.

Thankfully, these negative repercussions don’t occur because aircraft fuel evaporates instead of reaching the ground. 

In conclusion:

  • Airplanes dump fuel before landing because they need to lower the weight of the plane.
  • Planes have a safe maximum landing weight that they shouldn’t exceed so not to cause structural damage to the plane.
  • Dumping fuel is a very efficient way of reducing weight because aircraft fuel is heavy, weighing up to 6 pounds per gallon.
  • Airplanes also dump fuel before emergency landings because they need to rapidly reduce their weight before landing.
  • Most planes have a jettisoning fuel system in their wings that can be activated from the cockpit.
  • The system includes pumps and valves that remove the fuel like a contrail.
  • The jettisoned fuel has a negligible environmental impact because it evaporates before reaching the ground.

Helen Krasner holds a PPL(A), with 15 years experience flying fixed-wing aircraft; a PPL(H), with 13 years experience flying helicopters; and a CPL(H), Helicopter Instructor Rating, with 12 years working as a helicopter instructor.

Helen is an accomplished aviation writer with 12 years of experience, having authored several books and published numerous articles while also serving as the Editor of the BWPA (British Women Pilots Association) newsletter, with her excellent work having been recognized with her nomination of the “Aviation Journalist of the Year” award.

Helen has won the “Dawn to Dusk” International Flying Competition, along with the best all-female competitors, three times with her copilot.