You may have heard about a plane “dumping fuel” before. The definition of it is pretty self-explanatory…the plane has X amount of fuel and it throws out, or “dumps” (although the official term is “jettisons”) a certain amount while it’s in the air. It’s usually in conjunction with some sort of emergency landing.
So why do they do it?
In most cases, it’s to decrease the plane’s weight.
As we’ve mentioned before, airlines have thought of all sorts of crazy ways to decrease a plane’s weight. However that’s only to lower fuel costs…the less a plane weighs, the more efficiently it burns fuels. Just like how a 2021 Honda Civic, which weighs about 3,000 pounds, can get up to 42mpg but my 2017 Jeep Wrangler, which weighs over 4,000 pounds, gets half that (but, in her defense, my purple Jeep’s a whole lot cooler than a Honda Civic. No offense to you Honda Civic owners out there).
When it comes to planes though, they have two types of weight limits: the maximum takeoff weight and the maximum structural landing weight. Again, they’re both pretty self-explanatory: the former is the most that the plane can weigh so it will take off successfully, and the latter is the most weight the plane can be when it lands (Landing puts more stress on an airplane than taking off does. If the plane weighs less than the maximum structural landing weight, there’s little to no chance that the plane will suffer structural damage or break apart when landing [because yes, it could happen if the plane weighs too much]).
The maximum structural landing weight is always lower than the maximum takeoff weight. That’s because the plane will have been burning fuel the whole time it’s been in the air, which will decrease its weight (at a rate of roughly 6 pounds per gallon).
But let’s say there’s an emergency on the plane and the pilot determines or is instructed that they have to land NOW – maybe someone is having a heart attack or other major medical emergency, or perhaps it’s one of these more bizarre reasons that caused a plane to landed earlier than expected. Whatever the case, the plane will still have much more fuel than it normally would upon its expected landing, which could make it heavier than the maximum structural landing weight.
They have to get rid of the extra fuel to decrease the plane’s weight, so they dump it while they’re in the air.
From Wikipedia:
Fuel-dumping operations are coordinated with air traffic control, and precautions are taken to keep other aircraft clear of such areas. Fuel dumping is usually accomplished at a high enough altitude (minimum 6,000 feet above ground level), where the fuel will dissipate before reaching the ground. Fuel leaves the aircraft through a specific point on each wing, usually closer to the wingtips and farther away from engines, and initially appears as more liquid than vapor. Specific areas have been designated where fuel dumping is allowed to avoid damage or harm where the fuel may drop; generally speaking, this is above seas or unpopulated areas above land. Delta Air Lines Flight 89 is an example of fuel dumping that violated established regulations: on 14 January 2020, it dumped more than 10,000 gallons of fuel at a low altitude over a populated area in Los Angeles, causing injuries to 56 people including school children below.
From an environmental and health safety point of view, dumping fuel is not ideal. However because the fuel tends to get dumped at high levels in the atmosphere, and especially because it doesn’t happen very often, it’s not considered a major environmental or health hazard.
Feature Photo: Piqsels
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This post first appeared on Your Mileage May Vary
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