How does the specific range/fuel flow change during long range cruise of a jet airplane?

In long range cruise, the specific range, which is a measure of distance that a unit of fuel can propel the aircraft, tends to increase while the fuel flow decreases. This occurs because the aircraft operates at optimal conditions for fuel efficiency.

During long range cruise, pilots typically choose a higher altitude and lower power setting. At these conditions, the drag is minimized, allowing the aircraft to travel a greater distance per unit of fuel. Additionally, as the aircraft is cruising, it achieves a balance between lift and drag, which also contributes to a decrease in fuel consumption.

The lower fuel flow means that the engines are producing less thrust, which is more efficient for sustained flight over long distances. As a result, the relationship between specific range and fuel flow during this phase of flight is characterized by an increase in specific range and a decrease in fuel flow.