What would be the impact of a 15 knot headwind on fuel consumption for a 600NM flight?

A 15-knot headwind during a 600 nautical mile flight will increase the total fuel required for the trip. This is because headwinds directly oppose the aircraft's forward motion, effectively reducing the groundspeed. As the aircraft's true airspeed remains constant, the increased time spent in the air due to the headwind results in higher fuel consumption.

Flight duration will increase because the headwind acts as a barrier to progress, thus requiring the aircraft to burn more fuel over an extended period compared to a flight without such wind conditions. Moreover, the additional drag created by the headwind means the engines must work harder to maintain the same airspeed, further compounding fuel usage. Therefore, in this scenario, the impact of the headwind leads to a greater total fuel requirement.