<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by InterflugIL62:
This is all news to me as I have always heard of planes 'losing' fuel out over the ocean if they have to return to base and land.
I am sure the environmentalists have a field day with it. </font>
The fuel just evaporates and it is a relatively rare occurrence.
The reason fuel is sometimes dumped is because an aircraft's maximum gross landing weight can be significantly lower than it's maximum gross take-off weight because the stresses put on the plane during landing (and specifically the landing gear) are much greater than during take-off.
Most planes can be safely landed while exceeding the maximum gross landing weight (up to their maximum gross take-off weight), but require significant structural checks afterwords.