Which of the following scenarios would necessitate the activation of an ELT?

The activation of an Emergency Locator Transmitter (ELT) is specifically designed for use in emergency situations. In the context of the presented scenarios, an emergency landing situation is one that poses a serious threat to the safety of the aircraft and its occupants. This might include situations such as engine failures, control issues, or any circumstance where the pilot must land the aircraft in a location that may not be an airport, often due to an in-flight emergency.

When the ELT is activated during such instances, it emits a distress signal that greatly aids search and rescue operations, making it easier for rescuers to locate the downed aircraft. The signal can provide important data, such as location and aircraft identification, facilitating a quicker response.

Routine airborne adjustments, flying at cruising altitude, and loss of communication with air traffic control do not inherently indicate an emergency situation. These scenarios lack the immediate and serious threats that typically require an ELT to be activated, as they do not usually compromise the safety of the aircraft in the same way that an emergency landing would. Thus, such situations do not necessitate the activation of an ELT.