What is the radius of the MSA circle described?

• A. 15 NM
• B. 25 NM
• C. 35 NM
• D. 10 NM

Answer: (B)

The MSA circle is a defined safety area around a navigation aid that gives you a guaranteed obstacle clearance within a fixed distance. The standard radius for this circle is 25 nautical miles, which is why this problem’s described circle is 25 NM. This radius provides a consistent, conservative area around the VOR or aid so pilots can rely on a minimum altitude inside that circle even if their exact position isn’t precisely known. The other radii listed aren’t the typical MSA circle size used on standard IFR charts, which is why they don’t fit.