Summary

  • Dumping fuel mid-flight is a last resort for commercial airlines, only done when no other options are available to reduce landing weight and ensure safe landings.
  • Pilots try to avoid populated areas and other aircraft when dumping fuel, following strict guidelines. Incidents requiring fuel dumping are rare and have limited environmental impact.

Amid the often high costs of aviation fuel, the question arises as to why commercial airlines occasionally find it necessary to dispose of this valuable resource mid-flight. The answer to this seemingly puzzling situation lies in the considerations of landing weight and safety. Aircraft are meticulously engineered to touch down at or below predetermined weight thresholds, which are notably lower than their takeoff weights. This precaution is taken to minimize the risk of a forceful impact upon landing, which could potentially result in structural damage.

Dumping fuel is only done when no other options are available

Before a commercial airliner ever leaves the ground, a flight planner calculates how much fuel is needed for a particular flight. Unlike refueling a car, where one can simply top off the tank and continue driving, aircraft fueling follows a distinct process. Fuel put on aircraft is not measured in gallons or liters but pounds and kilos (since volume changes at varying flight temperatures). This is because when it comes to taking off and landing, weight is everything. The amount of fuel on a plane is calculated to have been burned off with a little to spare when the aircraft reaches its destination.

A LOT Boeing 787 Dreamliner receiving fuel
Photo: Stanislaw Tokarski/Shutterstock.

Fuel disposal through dumping is a measure reserved for situations where no alternatives remain feasible. Unless a flight has a severe problem or a medical emergency that requires the plane to land immediately, the pilots would rather keep flying in circles to burn off fuel rather than dump it.

If no choice is available, modern fuel jettisoning systems can dump thousands of pounds of fuel in seconds, allowing the aircraft to get to an allowable landing weight in less than 15 minutes. By using a combination of pumps and valves, fuel is diverted to the wingtips, where it is then expelled into the air. There is also a safety measure to ensure that the pilots don’t dump all the fuel but just enough so that it is safe to land.

Pilots try to avoid populated areas when dumping fuel

When a pilot decides to dump fuel, the Federal Aviation Administration (FAA) dictates that the aircraft must be 2,000 feet above the highest obstacle on its route, five miles from any other aircraft, and away from populated areas or water bodies.

Upon opting to release fuel mid-flight, airplane pilots initiate the process by flicking a switch within the cockpit. Subsequently, pumps are engaged to propel the fuel through nozzles situated in the wings. The dispensed fuel is spread out over a sufficiently large expanse, causing its particles to evaporate, transforming into a delicate mist.

This mist essentially transitions into a gaseous state, gradually blending into the atmospheric gases and becoming indistinguishable. Incidents involving the need to dump fuel are quite rare and is why environmental groups have not taken as much issue with it as one might expect.

Some planes don’t have fuel jettisoning systems

Depending upon the severity of the problem, pilots have three options:

  • Fly in circles to burn off excess fuel.
  • Jettison or dump fuel
  • Perform a hard landing

Of the three choices, the first two are self-explanatory, while the third choice of landing the plane heavy presents options. As we move away from four-engine aircraft like the Boeing 747, the Airbus A350, and the A380, many smaller twin-engine aircraft have no fuel jettisoning systems installed. This leaves them with two options (burn or land hard), rather than three. Did you know, for example, that the Boeing 757 can't dump fuel?

If a heavy landing is required, planes are inspected for damage before being allowed to fly again. One aircraft you never have to worry about with heavy landings is the Boeing 757, which has a similar takeoff and landing rating. While fuel dumping is an imperfect solution, its limited environmental repercussions underscore its occasional necessity to ensure safe landings.

However, the inability of some smaller planes to dump fuel can also create issues. For instance, Aeroflot's 2019 accident in which a Sukhoi Superjet 100 made an emergency landing in Moscow while still heavy with unburned fuel shows the dangers of not being able to dump fuel. Flames quickly engulfed the aircraft, leading to 41 people dying of the 78 onboard.

Have you ever been on a flight that had to jettison fuel? Let us know in the comments.