Which of the following indicates an emergency landing situation?

Engine failure is a critical situation that directly compromises the safety and control of an aircraft, necessitating an emergency landing. When an engine fails, the aircraft loses a significant amount of thrust, which can hinder its ability to maintain altitude and flight stability. Pilots must quickly assess the situation and initiate emergency protocols, including finding a suitable landing area and communicating with air traffic control.

The other situations don't indicate an emergency landing. Heightened cabin pressure is generally not a concern and does not warrant an emergency landing. Increased fuel efficiency is a typically positive operational parameter and would not signal any urgency. Lastly, normal instrument readings indicate that all systems are functioning properly, suggesting that an emergency landing is not necessary.