What Causes Aircraft To Need To Dump Fuel?

From time to time, we hear about an incident in which an aircraft has had to dump some of its fuel inflight. With jet fuel being an expensive commodity, this is not an action that is taken on a whim. As such, it only takes place under certain circumstances. But what are these?

Fuel Dump
Dumping fuel can help prevent an aircraft from landing overweight. Photo: Bobmil42 via Wikimedia Commons

Preventing overweight landings

The most common reason for aircraft to dump fuel is to keep them from landing above their maximum permitted weight. This will generally occur in instances when a flight needs to return to the airport shortly after departure. When making such a landing, the aircraft would otherwise still be laden with the extra weight of the fuel that it should have burned off en route to its destination.

This practice typically occurs when an aircraft needs to return to its origin, but time is not a critical factor. Such an incident took place last September when a New York-bound British Airways Boeing 777 squawked 7700 while over the Bristol Channel. At this point, it entered a hold at 10,000 feet and dumped fuel in the sea before returning to London Heathrow.

Stay informed: Sign up for our daily and weekly aviation news digests!

The nose of a Delta Air Lines Boeing 777-200ER dedicated to
A Delta 777 made headlines last year when it dumped fuel over an urban area. Photo: Getty Images

The BA incident was typical for a fuel dump in the sense that it did so over water. However, in January 2020, a Shanghai-bound Delta Air Lines 777 dumped fuel over urban Los Angeles after a compressor stall forced it to return to LAX. This saw Delta hit the headlines for the wrong reasons, as people on the ground were injured after coming into contact with the fuel.

Fuel dumping in the event of engine failures

It is also thought that, in years gone by, dumping fuel has improved the performance of aircraft that have suffered engine failures in emergencies. Nowadays, modern airliners are very well equipped to deal with such incidents. However, in earlier eras, engine failures made for a more threatening proposition.

As such, dumping fuel in these instances helped the aircraft to shed weight. This, in turn, is said to have made it easier for it to gain vital altitude, even under the power of one engine fewer than normal. The increased altitude would have given pilots more time to deal with the issue, and assess their options in the circumstances.

British Airways, Boeing 747, Bermuda
A British Airways Boeing 747 once flew from Los Angeles to Manchester on three engines. In not dumping its fuel and returning to LAX, it saved BA around $30,000 Photo: Vincenzo Pace | Simple Flying

When is fuel not dumped?

There are also some situations in which pilots have elected not to dump fuel, despite this being an option. One of these occurred in February 2005, involving a British Airways Boeing 747 flying from Los Angeles International (LAX) to London Heathrow (LHR).

In this instance, the aircraft suffered an engine fire shortly after takeoff. This would normally result in the flight returning to the airport, having dumped enough fuel to land at a safe weight.

However, as a Boeing 747 can safely fly on three engines, the pilots elected to continue their journey. The flight ultimately made it safely to the UK, although it landed in Manchester rather than London as a precaution, due to crew concerns about running out of fuel. Not dumping the fuel is said to have saved BA around $30,000.

The Boeing 757 cannot, but does not need to be able to, dump fuel. Photo: Vincenzo Pace | Simple Flying

There are also some aircraft on which dumping fuel is not an option in the first place. One of these is Boeing’s twin-engine 757 family. This is because the 757’s maximum landing weight is similar to its maximum takeoff weight. As such, there would be no need for the aircraft to lose weight before returning to an airport after takeoff in an emergency. This is why the aircraft is not equipped with the means to dump fuel.

Have you ever been on a flight where an aircraft has needed to dump fuel? If so, what was the reason for this? Let us know your thoughts and experiences in the comments.