Which system alert requires immediate attention if illuminated during flight?

In aviation, system alerts are crucial for ensuring the safety and efficiency of flight operations. The alert regarding an OBOGS (On-Board Oxygen Generating System) failure is critical because oxygen is essential for the pilot's ability to breathe and perform effectively, especially at high altitudes where the air is thin. If the OBOGS fails, the risk of hypoxia increases, which can impair cognitive and physical functions, potentially jeopardizing the safety of the flight.

While the other system alerts indicate significant issues, the implications of an OBOGS failure, particularly in the context of pilot health and safety, necessitate immediate attention. Ensuring that pilots have adequate oxygen supply is paramount for maintaining situational awareness and operational capability during flight. This makes the OBOGS failure alert an immediate priority among the given options.