What is the primary purpose of an aircraft's fuel jettison system?

The primary purpose of an aircraft's fuel jettison system is indeed to quickly achieve a lower landing weight. Aircraft must adhere to specific weight limits for safe landing, particularly when approaching the runway. If a flight is required to land unexpectedly or if it is necessary to return to an airport shortly after departure, the aircraft may find itself at a weight that exceeds safe landing limits due to the amount of fuel onboard.

By using the fuel jettison system, the flight crew can release excess fuel into the atmosphere, thereby reducing the weight of the aircraft to a manageable level. This capability ensures that the aircraft can safely land without risking structural integrity or control issues associated with landing at too high a weight.

Although fuel efficiency is important, the jettison system is not designed primarily for that purpose. It does not extend flight duration or improve engine performance as its main function is focused on safety and compliance with landing weight restrictions. Thus, the correct answer highlights the critical role fuel jettison systems play in enabling safe landings under various circumstances.