Which of these situations could indicate an emergency exists?

The situation that indicates an emergency exists is the unexpected loss of radar contact. When an aircraft loses radar contact, it can lead to significant safety concerns. Radar contact is crucial for maintaining situational awareness, navigation, and collision avoidance in the busy airspace. A loss of contact might mean that the flight could be in distress or deviating from its intended flight path, possibly due to mechanical issues, pilot error, or a loss of communication capabilities. Therefore, air traffic controllers need to treat this scenario with urgency, as it could signify an emergency situation that requires immediate attention and action.

Routine maintenance checks do not indicate an emergency; they are standard procedures performed to ensure the aircraft is operating safely. Normal descent to landing is also part of standard flight operations and should not be confused with emergency circumstances. Similarly, in-flight meal service issues, while they may be inconvenient for passengers and crew, do not relate to safety or emergency protocols.