Final answer:
Fuel jettison is a critical process that is utilized only in emergency situations to reduce the aircraft's weight for a safe landing or during aerial distress.
Step-by-step explanation:
Fuel jettison is a process that is generally advised to be carried out in specific conditions to ensure safety and compliance with regulations. Referring to the question, fuel jettison must only be carried out b) In an emergency. It is a last-resort procedure used to reduce the weight of an aircraft to ensure a safe landing or to deal with other critical situations where the aircraft is in distress. Fuel jettison is not a standard practice during normal operations such as takeoff or landing, nor is it conducted at low altitudes due to potential environmental and safety impacts.