Which guideline assists in determining when to provide service in emergencies?

The guideline that indicates when to provide service in emergencies is that LOA (Letter of Agreement) or FAA documents may outline specific situations or procedures that require air traffic controllers to offer assistance regardless of whether a request was made. These documents are designed to ensure safety and provide clear instructions on handling emergency situations.

In the context of air traffic control, when an emergency arises, it is vital for controllers to prioritize safety and follow established protocols. LOAs and FAA documents are authoritative resources that define how controllers should respond in emergencies, which may include offering service proactively. This ensures that the needs of the flight and the safety of all involved are prioritized, aligning with broader safety regulations and operational standards.

The other choices do not emphasize the established guidelines essential for emergency situations, which are critical for providing proper and timely service in such scenarios.