Prop Low Speed Mode cannot be used in which conditions?

• A. Cannot be used in icing conditions
• B. Can only be used in icing conditions
• C. Requires optical alignment
• D. Is inhibited above 20,000 ft

Answer: (A)

Prop Low Speed Mode is not available when icing conditions are present or anticipated. In icing, reducing propeller RPM would directly lower thrust and can worsen blade icing behavior, heat transfer, and anti-ice effectiveness. Keeping the prop in a higher-speed, more robust operating regime helps maintain adequate thrust, control, and ice protection, so the mode is inhibited in these conditions. The other options don’t reflect why this mode is restricted—ice is the real limiter, not optical alignment or altitude alone.