What auxiliary system is activated with the green ICE advisory message?

The green ICE advisory message is specifically associated with the activation of the ice protection system. This system is essential for ensuring that the aircraft operates safely in conditions where ice accumulation could interfere with performance, such as during flight in icy conditions or in clouds that contain supercooled water droplets. The ice protection system typically includes features such as wing and tail leading-edge heating and propeller de-icing to prevent ice build-up.

Understanding the context of this advisory is crucial for flight safety, as it informs the crew that the ice protection measures are active, which is necessary for maintaining optimal aerodynamic performance and control. The other options do not correlate with the green ICE advisory message, as they pertain to different auxiliary systems with distinct functions: environmental control deals with air temperature and pressure inside the cabin, the landing gear system pertains to the deployment and retraction of landing gear, and the hydraulic pressure system is involved in controlling various aircraft systems using hydraulic fluid.