If the aircraft experiences a tailwind enroute to its destination, in which direction will the critical point tend to move?

• A. toward the departure airport
• B. toward the destination airport
• C. halfway
• D. it does not change

Answer: (A)

The main idea is the point of no return, where the fuel left is just enough to get you back to the departure airport. With a tailwind on the outbound leg, you cover distance more quickly and use less fuel to reach a given point, but the return trip faces headwind and costs more fuel per mile. This combination shifts the break-even point closer to the departure airport.

If you set up the fuel balance for a point a distance x from departure, outbound fuel is proportional to x/(V + w) and return fuel is proportional to x/(V - w). Solving for the point where the remaining fuel equals the fuel needed to return gives x = F (V^2 − w^2) / (2 B V). Since w is positive, V^2 − w^2 is smaller than V^2, so x decreases. In other words, the critical point moves toward the departure airport when there’s a tailwind on the way out.