What condition is indicated by a green ALTN MODE on the ECAM air conditioning page?

A green ALTN MODE indication on the ECAM air conditioning page signifies that the aircraft's air conditioning system is operating in an alternate mode. This occurs specifically when a fault has been detected in the primary zone controller. In this situation, the system automatically switches to a backup mode to continue managing the cabin temperature and air distribution, ensuring comfort and safety for passengers and crew.

The alternate mode is a designed response to maintain functionality, indicating that while the primary system is compromised, the aircraft's systems are still operational and capable of providing necessary environmental controls. This proactive design helps pilots and crew manage potential issues without immediate risk to operations or passenger comfort.