In icing conditions, Mach below which value requires Engine ON?

• A. 0.50 M
• B. 0.52 M
• C. 0.60 M
• D. 0.55 M

Answer: (A)

In icing conditions, you want the engine running at low speeds to ensure the anti-ice and inlet conditions stay heated and stable. The threshold is 0.50 Mach: when the airspeed falls below this, the engine must be on to provide bleed air for anti-ice and to prevent ice buildup or compressor instability in the engine inlet. Once you’re above 0.50 Mach, the risk is reduced, so the requirement does not apply. That’s why 0.50 Mach is the correct threshold.