aviation aficionados, the idea that aircrafts sometimes dump fuel just after the take-off or right before they land might come as a surprise. But it turns out that the practice of “fuel dumping” or “fuel jettison” is a fairly well-established procedure used by planes primarily in certain emergency situations to reduce the aircraft’s weight.
While such overriding safety concerns are not as common an occurrence, a large-scale fuel dumping occurred on September 11, 2001, when U.S. airspace was closed due to the September 11 attacks.
Sometimes, this same concept of fuel dumping is used in what is called “a dump-and-burn” when fuel is ignited intentionally using the plane’s afterburner to create a spectacular flame for air shows or as a finale to fireworks 1.
Barring the circumstances when fuel is dumped and burnt for entertainment reasons, the practice of “fuel dumping” occurs when for one reason or the other an aircraft needs to land but its weight exceeds the maximum structural landing weight.
This could happen if the aircraft needs to change course or return to its point of departure. In such a situation, the aircraft is unlikely to have burn off enough fuel to make it lighter and for its weight to be within the maximum structural landing weight. As such, landing with that extra weight could cause damage to the aircraft. To avoid this and maximise passenger safety, some aircrafts can dump excess fuel.
Jets flying with US airlines in the 1950s and early 1960s tended to have fuel dump systems but today, a lot of planes do not have this feature as they are designed with possible overweight landings in mind. For example, a Boeing 757 has no fuel dump capability as its maximum landing weight is similar to its maximum take-off weight.
When there is a need and capacity to proceed with fuel dumping this is coordinated with air traffic control, and precautions are taken to keep other aircraft clear of such areas. Moreover, fuel dumping usually takes place at a high enough altitude so that the fuel will dissipate before reaching the ground. The speed with which fuel can be dumped varies but as an indication it is worth bearing in mind that the Boeing 747 dump rate for fuel ranges from one to two tonnes per minute1.
What is more if a fuel dump operation needs to occur, air traffic controllers are instructed to direct planes away from populated areas and over large bodies of water as much as possible. The same applies to military aircraft with most air bases only permitting fuel dumping in specified areas2.
Is fuel dumping safe for the environment?
While according to British Airways estimates quoted in the Inter-Governmental Panel on Climate Change (IPPC) report on “Aviation and the Global Atmosphere” published in 1999 “only a very small percentage (on the order of 0.01%) of fuel used by the aviation industry each year is jettisoned” 3, the US Environmental Protection Agency also regards fuel dumping as a very rare occurrence that airlines do not promote as it is not economically prudent to waste fuel. In contrast, US Air Force dumps fuel about 1,000 times a year with 7000 metric tons of fuel released to the atmosphere each year5.
The good news is that aircraft fuel, in particular what is used by the US Air Force, is highly volatile so it evaporates quickly. So, as analysis has shown, the effect of the evaporated fuel vapours in the atmosphere is negligible assuming the fuel is highly volatile and both pilot and air traffic controllers have ensured that fuel dumping does not happen unless a specific altitude has been reached.
According to the IPPC report, even if aircrafts also occasionally introduce hydrocarbons by jettisoning fuel at low altitudes in the troposphere, there is only a small increase of hydrocarbons in the region as the fuel evaporates3. But if the liquid fuel reaches the ground, there is a potential for negative environmental consequences such as crop damage or water pollution5.
Jet fuel is made up of various toxic hydrocarbons including benzene, which has been linked to cancer, but it also contains a number of additives including biocides to control bacterial and fungal growth in aircraft fuel systems. So there would be several risk if these kind of chemical mixtures came into contact with water resources, farmland or even urban greenspace. Exposure to benzene alone could affect plants by slowing their growth or even leading to their decay; it can also easily break down contaminate groundwater6.
Observed impacts of fuel dumping
If jet fuel were to routinely hit the ground it would pollute water resources and land, as well as damage crops and biodiversity. The impacts of some fuel reaching the ground were immediately visible to the population of Memphis in the United States who reported that “tiny dots appear to have burned onto leaves of all types of plants, and they appear different depending on the plant” while “on other plants, a white dust speckles the leaves and then destroys the green life underneath” 7.
The source of this damage even led to rumours that the BP Mexico Gulf spill might have created some sort of “toxic rain”. It was however eventually disclosed that FedEx, headquartered in Memphis, admitted to dumping jet fuel over the affected area dumping as much as 10,000 pounds of fuel onto the farmland7.
Critically, this is not the only known instance of fuel dumping that seems to have caused concerns among local residents. In May 2010, a Continental airplane encountered a malfunction and needed to return to Newark Airport so it had to dump 170,000 pounds of jet fuel over part of New Jersey. The Congressman representing that area called for an investigation into the environmental and health implications.
In 2009, a similar event took place after Asiana Airlines dumped about 5,000 gallons of fuel over Puget Sound, a sound along the north-western coast of the U.S. State of Washington. An oil sheen was seen on the water following the incident which led the State of Washington to open an investigation about the incident7.
What is perhaps most disappointing is that the State decided not to fine the airline even though its ecology department said some of the 5,000 gallons of fuel released from the plane reached the water8. Maybe this has something to do with the fact that the US EPA does not regulate the dumping of fuel during the course of a flight4.