Fuel Jettison, more commonly referred to as Fuel Dumping, is the intentional, controlled, jettison of fuel from an aircraft whilst in flight.
Most transport category aircraft have a maximum allowable takeoff weight that is in excess of the corresponding maximum landing weight. If the aircraft does not meet the regulatory engine out climb requirements at maximum takeoff weight or if the manufacturer has not made provisions to structurally allow for an "over-weight" landing capability , the aircraft will normally be equipped with a Fuel Dumping system.
Dumping System Criteria
If an aircraft’s design landing weight is less than that of the maximum takeoff weight and there is no provision for an over-weight landing, a situation could occur in which a landing might be necessary before sufficient fuel has burned off to lighten the aircraft. A Fuel Dumping system may be required on these aircraft to allow fuel to be jettisoned in flight to avoid structural damage caused by landing the aircraft when it is too heavy.
Fuel dumping systems must meet several standards. The average rate of fuel jettison must be at least 1 percent of the maximum weight per minute, except that the total time required to jettison the amount of fuel to reduce the aircraft weight from maximum takeoff to maximum landing need not be less than 10 minutes. For type certification, fuel jettisoning must be demonstrated at maximum weight with flaps and landing gear up and in a power-off glide at a speed 1.4 VS. It must also be demonstrated during climb with the critical engine inoperative and the remaining engines at maximum continuous power. Fuel jettisoning must also be demonstrated during level flight at 1.4 VS if the glide and climb tests show that this condition could be critical.
During the certification of the fuel dumping system, the manufacturer must demonstrate that the system operates without fire hazard. No fuel or fumes can enter any part of the aircraft. The fuel must also discharge clear of any part of the aircraft and the jettison operation must not adversely affect the controllability of the aircaft. The system must be designed so that any reasonably probable single malfunction in the system does not result in a hazardous condition due to asymmetrical dumping of, or inability to jettison, fuel. The fuel dump valve(s) must be designed to allow flight crewmembers to terminate the jettison operation at any time. Fuel dump systems are designed such that the fuel in the tanks normally used for takeoff or landing cannot be completely emptied.
Guidance for Flight Crew
The following general guidance is offered for flight crews:
- in all circumstances, follow manufacturer guidance for operation of the fuel dump system
- where a dump system is not fitted and the aircraft is heavier than maximum landing weight, ensure compliance with manufacturer criteria such as maximum touchdown rate of descent, minimum runway requirements, use of stopping devices, etc
- when appropriate, declare an emergency using the correct emergency communications protocols
- whenever practicable, advise ATC prior to commencing fuel dump. If the situation allows, follow ATC instructions on dumping location and height
- whenever practicable, dump fuel at or above an altitude that will allow evaporation or dissipation before the fuel reaches the ground. In most conditions, an altitude of 5000ft to 6000ft AGL is sufficient
- there is generally no manufacturer restriction regarding fuel jettison during an in-flight fire, whether inside or outside the airplane. However, in the event of an uncontrollable fire, crews are advised not to delay landing and subsequent evacuation in order to reduce the landing weight by dumping fuel