Buzz
What would prompt a pilot to purposely release an airplane's fuel? See more flight images.
©iStockphoto.com/sharply_doneMain Points
- Airplanes might need to release fuel before landing in emergency situations or due to maintenance concerns to reduce weight.
- Not every aircraft has a fuel-dumping system; it’s generally found on larger, wide-body planes as required by the FAA.
- Most of the dumped fuel evaporates before it reaches the ground, especially when released at higher altitudes or in warm weather, making fuel-dumping a safe but rarely necessary procedure.
With growing concerns about resource scarcity and rising oil prices, it seems odd that airplane pilots would intentionally release their fuel. What’s even more surprising is that they do it while in the air. Why is this considered acceptable, and even wise? Isn’t it dangerous to release fuel, potentially sparking a fire on the aircraft? And should we be worried about gasoline rain every time a plane flies overhead?
Although it may sound concerning, a fuel dump (formally referred to as fuel jettison) is a safe and well-reasoned procedure. It's also not as wasteful as it appears. In some cases, airlines find that dumping fuel is actually more cost-effective than not doing so. However, it's not something pilots do regularly. We spoke to Alison Duquette, a spokesperson for the Federal Aviation Administration (FAA), who confirmed that it's a rare occurrence.
It all boils down to the fact that certain aircraft are designed to be much lighter when landing than when taking off — sometimes by over 200,000 pounds (90,909.1 kilograms) [source: Boeing]. This might seem counterintuitive; you might think that taking off with a heavy load would be more difficult than landing with the same weight. However, landing places more strain on a plane. A plane that lands too heavy can hit the ground too hard, risking damage to the aircraft.
Fortunately, this issue often resolves itself. During the initial takeoff of a long-haul flight, a large commercial plane can carry tens of thousands of gallons of fuel, which at about 6.7 pounds per gallon can add up to hundreds of thousands of pounds of fuel [source: Conte]. However, throughout the flight, the aircraft consumes fuel, gradually losing weight. Aircraft manufacturers account for this in the design, ensuring the plane is light enough to land safely by the time it reaches its destination.
However, in some cases, an emergency may force a plane to land sooner than expected. This is when fuel dumping becomes necessary.
The Fuel Dumping Process
As previously mentioned, the difference between the maximum takeoff weight and maximum landing weight for a large commercial airplane can exceed 200,000 pounds. Imagine, soon after takeoff, a passenger experiences a medical emergency requiring an immediate landing, or the captain learns of a maintenance issue that needs urgent attention. Both of these situations are not unusual.
The pilot has several options. One option is to fly around, burning off fuel. The pilot can extend the landing gear or flaps to accelerate fuel consumption (or ‘dirty up the airplane’) [source: Getline]. However, this method is less than ideal in the case of a medical emergency.
Another option is to jettison fuel. This can be done with the flip of a switch in the cockpit. The system includes pumps and valves that allow fuel to be ejected from nozzles located on the aircraft’s wings. This system can eject thousands of pounds of fuel per minute, and the release appears similar to a contrail [source: Scott].
Not all airplanes are equipped with this advanced system, however. FAA spokesperson Alison Duquette mentions that narrow-body aircraft, such as the Airbus A320 or Boeing 757, are not designed with fuel dumping systems. On the other hand, larger wide-body planes like the Boeing 777 and 747, which have additional fuel tanks, are capable of fuel dumping. In fact, the FAA mandates that certain aircraft include fuel jettison systems [source: GPO].
Fortunately, most of the fuel will evaporate before it even reaches the ground. This is more likely when the aircraft is at higher altitudes, ideally above 5,000 feet (1,524 meters), and especially on warmer days. Since fuel jettison is rare and typically occurs in emergencies, Duquette notes that the FAA doesn’t have strict regulations for it. However, air traffic controllers assist pilots throughout the process, ensuring they are safely separated from other aircraft.
The final option in an emergency is to land the aircraft overweight. In fact, Boeing asserts that neither landing overweight nor fuel dumping has resulted in any accidents [source: Colella]. When time is critical during an emergency, landing overweight may be the best solution. However, if there is time, the damage to the aircraft (and the subsequent inspections and repairs) might prove more costly than fuel dumping. Ultimately, the decision rests on the pilot’s judgment in the given circumstances.
Although the fuel is likely to evaporate before it reaches the ground, it is true that it remains suspended in the atmosphere for a time. Boeing highlights that this can lead to an unpleasant odor and that the vaporized fuel will eventually settle to the ground. [source: Colella].
