Vertical separation may be reduced to 800 feet when inside how many nautical miles?

• A. 10 nm
• B. 15 nm
• C. 20 nm
• D. 12 nm

Answer: (D)

The key idea here is that vertical separation can be tightened under radar surveillance when aircraft are within a limited, well-covered area. In standard radar-controlled airspace, 1000 feet of vertical separation is typical, but inside a defined inner radar service area, the controller can apply an 800-foot vertical separation if both aircraft are being actively radar-tracked and the normal conditions for safe spacing are met (same direction, same flight path or heading, appropriate lateral separation, etc). The distance defining that inner area is 12 nautical miles, which is why this option is the correct choice. Beyond that 12 NM boundary, the tighter 800-foot separation isn’t allowed, and the standard 1000-foot separation applies.