Fuel dumping
The fuel dumping (literally: unloading of fuel) is a technique which consists in emptying the fuel tanks of a plane in flight in the event of urgency whereas it has just taken off and must land as fast as possible.
In a general way, a plane has two types of limitation of weight. The first is the maximum mass on takeoff, the second the maximum mass with the landing, which is always smallest of both. In normal weather, that makes it possible a plane to take off with maximum mass, to consume fuel in flight and to arrive at destination with a less weight (there are other variables influence the maximum masses, but they will not be taken into account here for more simplicity).
It is during a flight which leaves the routine that the maximum mass with the landing can pose problem. If a plane takes off with maximum mass and must face an unspecified situation which obliges it to turn over to its Aéroport starting (engineering problems, faintness of a passenger…), it will not have time to consume the fuel necessary and will be above the maximum mass to the landing.
When the first jet commercial made their appearance at the end of the Fifties, FAA founded a law stipulating that if the difference between the maximum mass on takeoff and the maximum mass with the landing exceeds 105%, the apparatus must be provided with a system of evacuation of the fuel. Planes like the Boeing 707 and of the Douglas DC-8 were then equipped with it. If one of these planes were to turn over towards the airport from where it had taken off, it would be enough for him to just release enough fuel to bring back its mass below its maximum mass to the landing, then to land.
Into the Sixties, Boeing introduced the 757 and Douglas DC-8, the original models of these two planes being short-distance carriers, the law of the 105% was not a solution. But of the alternatives appeared, been driven by more powerful engines JT8D. Their autonomy increased, like their mass, making them incompatible with the law of the 105%. The installation of system of evacuation of fuel being too expensive, the FAA abolishes the law of the 105%, provided that the apparatuses respect standards FAR 25.119 and FAR 25.121 after a 15 minutes flight. In other words, one needs that the plane (overloaded) can land with the shutters extended to the maximum and the two engines under operation, respectively with an engine out-service.
Since, the majority of the twin-jet aircrafts reach these requirements. Boeing 737 (all models), the Douglas DC-9/MD-80 and Boeing 717, the family A320 and of many jet regional are not equipped with system of fuel-dumping . In the case of an urgency which requires a return to the fast starting airport, the pilots have as instructions to go down while describing circles in order to burn fuel, even, if the situation requires it, simply to land. The recent planes are designed to be able to land in overweight in exceptional cases, with the help of a thorough inspection. Many films and television news claim that all the planes can release fuel, but in fact, the major part is unable. Under certain weather conditions (high moisture of the air), the planes flying at low altitude leave trails of condensation which are formed above and at the ends of the wings. Observers take sometimes this phenomenon for a fuel dropping, whereas it is only of the steam. This condensation is due to the depression formed by the depression generated by the plane.
The twin-jet aircrafts with longer operating range such as Boeing 767 and 777, a300 Airbus, A310 and A330 do not have a system of evacuation of the fuel this parameter depends on the date of order or the desires of the customer. The sorting and four-jet aircrafts like the L-1011, McDonnell Douglas MD-11, Boeing 747 and the airbus A340 generally have problems to reach standard FAR 25.119 when they take off with maximum mass. This is why almost all these planes have a system of fuel dropping. Boeing 757 is deprived by it because its two maximum masses are close.
Nowadays, the operations of fuel dropping are managed by the control of the air traffic, which takes care that no other apparatus is in a drop zone. They are usually carried out at a rather high altitude so that the fuel is dissipated before touching the ground. The fuel leaves the plane by opening being located close to the end of the wings, but in order to as much as possible move away them from the engines. The use of this process on the broadest scale took place the September 11th 2001 when many planes are transfered to refuse the right to enter the American airspace (consequence of the attacks). Flights were deviated towards Newfoundland in Canada or had to turn over to their starting airport. For the middle-distance carriers unable to land in overweight, the only exit was to get rid of part of their kerosene.
Dump-and-burn
The dump-and-burn is a fuel dumping where the fuel is intentionally ignited by the slopes of Post-combustion of the engine of the plane. The generated spectacular flame combined at a high speed makes dump-and-burn a popular figure at the time of air meetings or like final bouquet for a fireworks. This practice is also known under the name of “torch” or “zippo”.
The Australian F-111 are often used for this purpose, in particular at the time of the closing ceremony of the Olympic Games. The pilots described this experiment like exciting, even if themselves cannot see the flame, but just an orange gleam in the sky, the immense flame producing an intense light.
Certain sources claim that USAF would have given up this practice for reasons of costs and safety.
The dump-and-burn is seldom used in combat, except for the lighting of a zone for a night observation but never at the time of an active combat (the plane would become very vulnerable). It can also be used like deludes against a missile with infra-red guidance or to plug an enemy by generating a smoke screen.
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