 | This article needs additional citations for verification .(October 2020) |
Fuel dumping (or a fuel jettison) is a procedure used by aircraft in certain emergency situations before a return to the airport shortly after takeoff, or before landing short of the intended destination (emergency landing) to reduce the aircraft's weight.
Aircraft have two major types of weight limits: the maximum takeoff weight and the maximum structural landing weight, with the maximum structural landing weight almost always being the lower of the two. This allows an aircraft on a normal, routine flight to take off at a higher weight, consume fuel en route, and arrive at a lower weight.
It is an abnormal, non-routine flight where landing weight can be a problem. If a flight takes off at the maximum takeoff weight and then must land well before its destination, even returning immediately after takeoff to the departure airport (for example, because of mechanical problems or a passenger medical problem), it will contain more fuel than was intended for landing. If an aircraft lands at more than its maximum allowable weight, it might suffer structural damage or even break apart on landing.
As jets began flying in the US in the late 1950s and early 1960s, the FAA rule in effect at the time mandated that if the ratio between an aircraft's maximum structural takeoff weight and its maximum structural landing weight was greater than 1.05, the aircraft had to have a fuel-dump system installed. Aircraft such as the Boeing 707 and 727 and the Douglas DC-8 had fuel dump systems. Any of those aircraft needing to return to a takeoff airport above the maximum landing weight would jettison an amount of fuel sufficient to reduce the aircraft's weight below that maximum landing weight limit, and then land.
During the 1960s, Boeing introduced the 737, and Douglas introduced the DC-9, the original models of each being for shorter routes; the 105% figure was not an issue, thus they had no fuel-dump systems installed. During the 1960s and 1970s, both Boeing and Douglas "grew" their respective aircraft as far as operational capabilities were concerned via Pratt & Whitney's development of increasingly powerful variants of the JT8D engines that powered both aircraft series. Both aircraft were now capable of longer duration flights, with increased weight limits, and complying with the existing 105% rule became problematic due to the costs associated with adding a fuel-dump system to aircraft in production. Considering the more powerful engines that had been developed, the FAA changed the rules to delete the 105% requirement, and Federal Aviation Regulations 25.1001 was enacted stating a jettison system was not required if the climb requirements of FAR 25.119 (Landing Climb) and FAR 25.121 (Approach Climb) could be met, assuming a 15-minute flight. In other words, for a go-around with full landing flaps and all engines operating, and at approach flap setting and one engine inoperative, respectively.
Since most twin jet airliners can meet these requirements, most aircraft of this type such as the Boeing 737 (all models), the DC-9/MD80/Boeing 717, the A320 family and various regional jet ("RJ") aircraft do not have fuel dump systems installed. In the event of an emergency requiring a return to the departure airport, the aircraft circles nearby in order to consume fuel to get down to within the maximum structural landing weight limit, or, if the situation demands, simply land overweight without delay. [4] Modern aircraft are designed with possible overweight landings in mind, but this is not done except in cases of emergency, and various maintenance inspections are required afterwards.
Long-range twin jets such as the Boeing 767 and the Airbus A300, A310, and A330 may or may not have fuel dump systems, depending upon how the aircraft was ordered, since on some aircraft they are a customer option. Three- and four-engine jets like the Lockheed L-1011, McDonnell Douglas DC-10 / MD-11, Boeing 747 and Airbus A340 usually have difficulty meeting the requirements of FAR 25.119 near maximum structural takeoff weight, thus most of those have jettison systems. A Boeing 757 has no fuel-dump capability as its maximum landing weight is similar to the maximum take-off weight.
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, AGL), 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. [5]
It is difficult to quote specific dump rates even for specific types of aircraft since the dumped fuel is not pumped but delivered by gravity feed so as to be more independent of electrical systems, which might be unavailable in a fuel-dump scenario. This means the actual rate depends on the pressure exerted by the fuel head: the more fuel on board, the higher the rate at which it flows out. This also means that the dump rate is not constant, but decreases while dumping because the fuel head and its pressure decrease.
As a rule of thumb for the Boeing 747, pilots either quote dump rates ranging within 1–2 tons per minute or reference a thumb formula of dump time = (dump weight / 2) + 5 in minutes. [6] In 2009, an Airbus A340-300 returning to its airport of departure shortly after takeoff [7] dumped 53 tons of fuel in 11 minutes. [8]
The average rate of descent of the dumped fuel is approximately 500 feet per minute (2.5 m/s). Air traffic control, after receiving information from the pilots executing the dumping procedure, usually separates other traffic by 2,000 feet (610 m) vertically and 5 nautical miles (9.3 kilometres) laterally, since the dumped vapours if ingested by a jet engine might cause serious problems to the engine's normal operation.
A dump-and-burn is a fuel dump in which the fuel is ignited, intentionally, using the plane's afterburner. A spectacular flame combined with high speed makes this a popular display for air shows or as a finale to fireworks. Dump-and-burns are also referred to as "torching" or "zippos".
The General Dynamics F-111 Aardvark's dump and burn is so powerful that it can set a runway on fire, as the flame burns rubber from skid marks. [9] The aircraft has been used for this purpose in Australia during the closing ceremony of the 2000 Summer Olympics [10] and (until 2010) regularly at Brisbane's Riverfire and the Australian Grand Prix. The F-111 is ideally suited to perform the dump-and-burn maneuver, as its fuel dump nozzle is located between the engine exhausts.
The Boeing 777, commonly referred to as the Triple Seven, is an American long-range wide-body airliner developed and manufactured by Boeing Commercial Airplanes. The 777 is the world's largest twinjet and the most-built wide-body airliner. The jetliner was designed to bridge the gap between Boeing's other wide body airplanes, the twin-engined 767 and quad-engined 747, and to replace aging DC-10 and L-1011 trijets. Developed in consultation with eight major airlines, the 777 program was launched in October 1990, with an order from United Airlines. The prototype was rolled out in April 1994, and first flew in June. The 777 entered service with the launch operator United Airlines in June 1995. Longer-range variants were launched in 2000, and first delivered in 2004.
The McDonnell Douglas DC-10 is an American trijet wide-body aircraft manufactured by McDonnell Douglas. The DC-10 was intended to succeed the DC-8 for long-range flights. It first flew on August 29, 1970; it was introduced on August 5, 1971, by American Airlines.
The Airbus A340 is a long-range, wide-body passenger airliner that was developed and produced by Airbus. In the mid-1970s, Airbus conceived several derivatives of the A300, its first airliner, and developed the A340 quadjet in parallel with the A330 twinjet. In June 1987, Airbus launched both designs with their first orders and the A340-300 took its maiden flight on 25 October 1991. It was certified along with the A340-200 on 22 December 1992 and both versions entered service in March 1993 with launch customers Lufthansa and Air France. The larger A340-500/600 were launched on 8 December 1997; the A340-600 flew for the first time on 23 April 2001 and entered service on 1 August 2002.
The Airbus A330 is a wide-body aircraft developed and produced by Airbus. Airbus conceived several derivatives of the A300, its first airliner from the mid-1970s. Then the company began development on the A330 twinjet in parallel with the A340 quadjet and launched both designs with their first orders in June 1987. The A330-300, the first variant, took its maiden flight in November 1992 and entered service with Air Inter in January 1994. The slightly shorter A330-200 variant followed in 1998.
A wide-body aircraft, also known as a twin-aisle aircraft and in the largest cases as a jumbo jet, is an airliner with a fuselage wide enough to accommodate two passenger aisles with seven or more seats abreast. The typical fuselage diameter is 5 to 6 m. In the typical wide-body economy cabin, passengers are seated seven to ten abreast, allowing a total capacity of 200 to 850 passengers. Seven-abreast aircraft typically seat 160 to 260 passengers, eight-abreast 250 to 380, nine- and ten-abreast 350 to 480. The largest wide-body aircraft are over 6 m (20 ft) wide, and can accommodate up to eleven passengers abreast in high-density configurations.
A jet airliner or jetliner is an airliner powered by jet engines. Airliners usually have two or four jet engines; three-engined designs were popular in the 1970s but are less common today. Airliners are commonly classified as either the large wide-body aircraft, medium narrow-body aircraft and smaller regional jet.
The McDonnell Douglas MD-11 is an American tri-jet wide-body airliner manufactured by American manufacturer McDonnell Douglas (MDC) and later by Boeing. Following DC-10 development studies, the MD-11 program was launched on December 30, 1986. Assembly of the first prototype began on March 9, 1988. Its maiden flight occurred on January 10, 1990, and it achieved Federal Aviation Administration (FAA) certification on November 8. The first delivery was to Finnair on December 7 and it entered service on December 20, 1990.
Thrust reversal, also called reverse thrust, is the temporary diversion of an aircraft engine's thrust for it to act against the forward travel of the aircraft, providing deceleration. Thrust reverser systems are featured on many jet aircraft to help slow down just after touch-down, reducing wear on the brakes and enabling shorter landing distances. Such devices affect the aircraft significantly and are considered important for safe operations by airlines. There have been accidents involving thrust reversal systems, including fatal ones.
In aviation, hot and high is a condition of low air density due to high ambient temperature and high airport elevation. Air density decreases with increasing temperature and altitude. The lower air density reduces the power output from the aircraft's engine and also requires a higher true airspeed before the aircraft can become airborne. Aviators gauge air density by calculating the density altitude.
A deadstick landing, also called a dead-stick landing, is a type of forced landing when an aircraft loses all of its propulsive power and is forced to land. The "stick" does not refer to the flight controls, which in most aircraft are either fully or partially functional without engine power, but to the traditional wooden propeller, which without power would just be a "dead stick". When a pilot makes an emergency landing of an aircraft that has some or all of its propulsive power still available, the procedure is known as a precautionary landing.
A twinjet or twin-engine jet is a jet aircraft powered by two engines. A twinjet is able to fly well enough to land with a single working engine, making it safer than a single-engine aircraft in the event of failure of an engine. Fuel efficiency of a twinjet is better than that of aircraft with more engines. These considerations have led to the widespread use of aircraft of all types with twin engines, including airliners, fixed-wing military aircraft, and others.
A takeoff/go-around switch is a switch on the autothrottle of modern large aircraft, with two modes: takeoff (TO) and go-around (GA). The mode is dependent on the phase of flight; usually, on approach to land, the autopilot will be set to approach mode, therefore if the TO/GA switch is pressed it will activate the go-around mode of the autothrottle (about 90–92% N1, if pressed again, go around thrust will increase to full ; conversely, when takeoff is set on the autopilot, the switch activates takeoff mode of the autothrottle. On Boeing aircraft TO/GA modes are selected by a separate button near the throttle levers, but on Airbus aircraft it is activated by advancing the thrust levers forward to the TO/GA detent.
A turbine engine failure occurs when a turbine engine unexpectedly stops producing power due to a malfunction other than fuel exhaustion. It often applies for aircraft, but other turbine engines can fail, like ground-based turbines used in power plants or combined diesel and gas vessels and vehicles.
Emirates Flight 407 was a scheduled international passenger flight operated by Emirates from Auckland to Dubai with a stopover in Melbourne, operated by an Airbus A340-500 aircraft. On 20 March 2009, the flight failed to take off properly at Melbourne Airport, hitting several structures at the end of the runway before climbing and then returning to the airport for a safe landing. Although no fatalities or injuries resulted, damage to the aircraft was severe enough for the event to be classified by Australian Transport Safety Bureau as an "accident". It was subsequently determined that a data-entry error resulted in insufficient engine thrust during take off. It has been described "as close as we have ever come to a major aviation catastrophe in Australia" by aviation officials.
The aircraft gross weight is the total aircraft weight at any moment during the flight or ground operation.
The maximum landing weight (MLW) is the maximum aircraft gross weight due to design or operational limitations at which an aircraft is permitted to land. The MLW is set in order to ensure safe landings; if an aircraft weighs too heavy during touchdown, it may suffer structural damage or even break apart upon landing. Aircraft also have a maximum take-off weight, which is almost always higher than the maximum landing weight, so that an aircraft can weigh less upon landing due to burning fuel during the flight.
A four-engined jet, sometimes called a quadjet, is a jet aircraft powered by four engines. The presence of four engines offers increased power, allowing such aircraft to be used as airliners, freighters, and military aircraft. Many of the first purpose-built jet airliners had four engines, among which stands the De Havilland Comet, the world's first commercial jetliner. In the decades following their introduction, their use has gradually declined due to a variety of factors, including the approval of twin-engine jets to fly farther from diversion airports as reliability increased, and an increased emphasis on fuel efficiency.
Delta Air Lines Flight 89 was a scheduled flight from Los Angeles International Airport (LAX) to Shanghai Pudong International Airport (PVG). On January 14, 2020, the Boeing 777-200ER conducting the flight had engine problems shortly after takeoff; while returning to the origin airport for an emergency landing, it dumped fuel over populated areas adjacent to the city of Los Angeles, resulting in skin and lung irritation in at least 56 people on the ground and triggering a Federal Aviation Administration (FAA) investigation. The aircraft landed safely with no injuries to passengers or crew.
