What should you do after the EICAS displays an APU FUEL SOV FAIL Caution message?

When the EICAS (Engine Indication and Crew Alerting System) displays an "APU FUEL SOV FAIL" caution message, it indicates that there is an issue with the APU's fuel shutoff valve. In this situation, the appropriate response is to turn the APU switch OFF after waiting a brief period of 2 seconds. This wait time allows the system to stabilize and properly assess the situation.

Turning off the APU is necessary to prevent potential further issues, such as fuel leakage or failure of the APU system, which could lead to safety concerns. By deactivating the APU, the aircraft's systems can be evaluated, and maintenance can be performed when on the ground without risking further complications.

The other actions may not contribute effectively to resolving the caution displayed. For instance, just turning on the APU switch for 2 seconds would not address the underlying problem and could potentially exacerbate fuel system issues. Simply waiting for 90 seconds without taking any action does not provide a proactive approach to handling the caution, which is crucial for safety and operational integrity.