If you need to lose 8,000 feet of altitude, how far out should you begin your descent at a groundspeed of 400 knots?

To determine how far out to begin your descent to lose 8,000 feet of altitude at a groundspeed of 400 knots, you can use a general rule of thumb in aviation: for every 1,000 feet of descent, you should start your descent approximately 3 nautical miles (nm) from your target altitude.

In this case, to lose 8,000 feet, you would multiply 8 (the number of thousands of feet) by 3 (the distance in nautical miles per thousand feet). This calculation gives you:

8,000 feet ÷ 1,000 = 8

8 × 3 = 24 nm

Therefore, you should begin your descent 24 nautical miles away from your desired altitude, which aligns with the correct answer. This rule helps ensure a smooth and controlled descent, allowing for proper adjustments based on the specific aircraft's performance and environmental factors.