Under what conditions should access to the ILS critical area be restricted?

• A. When the ceiling is below 800 ft and visibility below 2 SM
• B. When the ceiling is below 600 ft and visibility below 1 SM
• C. When the ceiling is below 1000 ft and visibility below 3 SM
• D. When the ceiling is below 200 ft and visibility below 2,000 ft

Answer: (A)

Protecting the ILS critical area is about keeping the area free from interference when aircraft rely on instruments rather than visual cues. When weather conditions are IMC or near IMC, pilots may not be able to see and avoid the critical area, so access should be restricted to prevent any ground traffic or personnel from entering and potentially disturbing the localizer or glideslope signals.

The threshold used here is when the ceiling is below 800 feet and visibility is below 2 statute miles. At or below these levels, instrument flight becomes necessary, and restricting access helps ensure the ILS signals can be received clearly by approaching aircraft.

Other weather thresholds don’t align with this protection rule. For example, higher minima like ceiling 1000 feet and 3 miles are typical basic VFR criteria rather than the specific ILS protection threshold, and much lower or nonsensical values aren’t part of the standard protection guidance.