When is a notification of overdue aircraft required?

A notification of overdue aircraft is required when there is a suspicion that an aircraft might be involved in an accident. This requirement stems from the need to ensure the safety of the occupants and to enable a swift response from search and rescue operations. If an aircraft is suspected to be in an accident, prompt notification to the appropriate authorities can help initiate the necessary search efforts, which is crucial in potentially life-threatening situations.

The other scenarios, while relevant to general aircraft operations, do not specifically trigger a requirement for an overdue notification. For instance, while an aircraft being within 30 minutes of the expected landing time might suggest it is late, it does not inherently indicate an emergency. Similarly, even if an aircraft has not communicated for a certain duration, this does not necessarily imply an accident has occurred; the aircraft could simply be experiencing communication issues. Lastly, an aircraft missing for over 24 hours certainly requires attention, but the immediate need for notification is tied more directly to the indication of an accident.