Is this a waste of fuel?

That does seem like a waste of fuel. If it is, what happens to it after it’s dumped? I will have to watch for that, as I live on a flight path. Perhaps the purpose is to lessen the possibility of fire or explosion if there’s problems landing?

This is done in various emergency situations.

It’s also done if the plane is landing with more fuel than anticipated, causing the craft to touch down with a higher than manufacturer recommended landing weight.

They may be dumping for two basic reasons: Reducing weight to shorten the roll out distance when forced to land on a shorter runway. To lessen the fire hazard if there is a malfunction on the aircraft and there is a greater likelihood of some kind of crash. The airline doesn’t want to throw fuel away unless it is really necessary for safety.

During the final stage of the approach or landing, under certain weather conditions there can be seen contrails from the wing tops. These depend on the condensation of water vapor due to the negative pressure creates the wing geometry. A common perception is that this is fuel emissions, which is not true. Only big planes have arrangements for fuel dumps, which are made in emergency situations and controlled and lead from the flight tower, and done over unpopulated areas. The fuel dissipates in the air.

@Jacket Correct. Not a routine occurrance. +GA

The airlines do not dump fuel unless it is an emergency. Fuel is like gold to the airlines.

@Jacket is correct- what you see as they land is water vapor off the wings.