What is an ALNOT issued for?

An ALNOT, or Alert Notice, is specifically issued to alert support services regarding a potential overdue aircraft. The underlying purpose of this action is to ensure that appropriate measures are taken to locate the aircraft and assist any passengers or crew who may be in distress or at risk. When air traffic control or other responsible agencies have not received communications from an aircraft for a specified amount of time, the issuance of an ALNOT prompts search and rescue operations or other necessary actions to locate the aircraft, thereby enhancing aviation safety.

The misinformation alerts in the other options do not align with the function of an ALNOT. While turbulence warnings are important for in-flight safety, they are communicated through different channels. Weather updates are also crucial but are disseminated separately from ALNOTs. Lastly, while information about navigation aids is essential for pilots, it does not fall under the purpose of alerting support services about overdue aircraft.