Welcome to your interview.
The question is on your right: Unexpected System Failure Response. Take a moment with it first.
Talk your thinking through with me if you like - when you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes). Discussion and graded submissions share your five interviewer interactions, so spend them well.
Describe a situation where an operational system failed unexpectedly. What immediate steps did you take to mitigate the impact?