Under icing conditions, when outside temperature is less than -9 C, how often must 70% N1 be applied?

Under icing conditions, when outside temperature is less than -9 C, how often must 70% N1 be applied?

• A. every 5 minutes
• B. every 15 minutes
• C. every 10 minutes
• D. every 20 minutes

Answer: (C)

When aircraft are in icing conditions, ice can form in the engine inlet and on anti-ice surfaces, so the engine needs periodic attention to prevent ice from building up. Applying 70% N1 at regular intervals helps push airflow through the engine, so ice that begins to form is dislodged and the anti-ice system remains effective without constantly running at high power. At outside temperatures below -9 C, the standard practice is to apply 70% N1 every 10 minutes. This interval strikes a balance: it provides timely management of ice buildup without unnecessary fuel burn from more frequent high-N1 runs, and it’s short enough to prevent ice from accumulating between cycles. Longer intervals could allow significant ice buildup, while shorter ones would add unnecessary operational cost.

When aircraft are in icing conditions, ice can form in the engine inlet and on anti-ice surfaces, so the engine needs periodic attention to prevent ice from building up. Applying 70% N1 at regular intervals helps push airflow through the engine, so ice that begins to form is dislodged and the anti-ice system remains effective without constantly running at high power.

At outside temperatures below -9 C, the standard practice is to apply 70% N1 every 10 minutes. This interval strikes a balance: it provides timely management of ice buildup without unnecessary fuel burn from more frequent high-N1 runs, and it’s short enough to prevent ice from accumulating between cycles. Longer intervals could allow significant ice buildup, while shorter ones would add unnecessary operational cost.