The anti-ice system on the Beechjet 400A should be used at ram air temperatures of at most what, unless icing conditions are indicated?

• A. 10 °C or less
• B. -5 °C or less
• C. 0 °C or less
• D. 20 °C or less

Answer: (A)

Ice can form on exposed surfaces when moisture is present and the air is cold enough, so anti-ice is used to prevent that buildup in the conditions where icing is possible but not in all temperatures. For the Beechjet 400A, the maintenance and flight procedures specify activating the anti-ice system when ram air temperature is at or below 10 °C, unless icing conditions are indicated. This means you preempt ice formation in marginal icing conditions without unnecessarily using anti-ice in warmer air. If you do see icing conditions (like visible moisture, freezing drizzle, etc.), you would use anti-ice regardless of temperature. Using a threshold higher than 10 °C would expose you to icing risk in warmer air, while a lower threshold would leave potential icing unchecked in the 0–10 °C range, and a threshold like 20 °C would waste bleed-air and could cause unnecessary heat.