When is ADS Probe heat required on the ground?

Probe heat for the Air Data System (ADS) is necessary on the ground when the outside air temperature (OAT) is at or below freezing (0°C or 32°F) and there is visible moisture present. This requirement is crucial because moisture can freeze on the probes, potentially leading to inaccurate airspeed, altitude, or vertical speed readings, which are critical for safe flight operations. Ensuring the probes are adequately heated prevents the formation of ice that can block the sensors, thereby maintaining their functionality while the aircraft is on the ground.

When the OAT is above 10°C, the need for probe heat is typically not necessary, as ice formation is unlikely. Similarly, the requirement does not apply when the aircraft is airborne since the airflow and design of the aircraft helps prevent ice accumulation on the probes. Hence, the specific condition of having an OAT at or below 0°C with visible moisture triggers this precaution for safety and operational integrity.