Which situation would require immediate attention during flight?

Warning lights indicating potential issues during flight are critical signals that directly pertain to the safety and functioning of the aircraft. These warning systems are designed to alert the crew to malfunctions or irregularities, such as engine performance issues, electrical system failures, or other essential operational anomalies. When such lights are lit, it suggests that immediate evaluation and potentially corrective action is necessary to ensure the aircraft remains within safe operating parameters.

In contrast, normal cruising altitude and steady instrument readings indicate that the aircraft is operating properly under stable conditions, posing no immediate concern. Clear weather conditions also imply a safe flight environment but do not necessitate urgent action. Therefore, the presence of warning lights is the only scenario that demands immediate attention to maintain the safety of the flight.