For some aircraft types, the maximum allowable landing weight is substantially less than the aircraft's take-off weight. The Boeing 747, 777, and Airbus A380s are examples, and these three aircraft types do have fuel dumping capabilities.
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Larger planes like the Boeing 747, on the other hand, have fuel jettison systems. If the aircraft tried to land without dumping the fuel first, it is considered an overweight landing attempt and could place immense stress on the airframe. It could also increase the risk of fire and fuel leaking onto the tarmac.
Some A330s have fuel dumps and some don't. It is/was an option. Even so, fuel dumping is generally only reserved for those times when it's necessary. If the need to land is not pressing (not all emergencies demand an immediate landing), then the crew may elect to just “burn off” the fuel rather than dump it.
#21271129. They circle to burn fuel like every other aircraft that can't dump fuel. If needs be & they must land heavy well then the aircraft may be damaged & a runway/airport closure could follow.
On the other hand, Federal Aviation Regulations require certain aircraft, like the Boeing 747 for instance, to have a fuel jettison system. The same holds true for Airbus aircraft; the Airbus A340 and A380 can dump fuel, while the A320 cannot. All Boeing 747 aircraft have a fuel jettison system.
It would seem strange that pilots would purposefully dump fuel from their aircraft at a time when fuel prices have skyrocketed. What's more bizarre is that they do it in the air while flying. Tossing fuel into the air is a safe procedure for a good reason. Additionally, it is not as wasteful as it seems.
There are two reasons for this, one related to the aircraft itself and the other to how they are used on transpacific flights. Aircraft with four engines, or “quads”, tend to be less fuel-efficient than twinjets due to inherent design factors such as a higher wing weight and a smaller engine fan diameter.