The white light above the wing deice switch illuminates when the wing temperature sensor senses approximately what temperature?

• A. 32 degrees F
• B. 212 degrees F
• C. 0 degrees F
• D. Approximately 140 degrees F

Answer: (D)

The indicator is tied to the wing’s temperature sensor and serves as a readiness check for the wing anti-ice system. When the wing skin reaches roughly 140°F (about 60°C), the white light above the deice switch comes on to show that the heating elements have brought the leading edge up to a temperature high enough to effectively prevent ice buildup and allow continued anti-ice protection. This temperature is chosen because it’s well above freezing and ensures ice won’t re-form, while avoiding unnecessary overheating of the wing.

The other temperatures listed aren’t used as the threshold for this indicator. They don’t represent the specific heat level needed for reliable ice protection, whereas 140°F is the operational target for this system.