When is it necessary to file a flight plan?

Filing a flight plan is primarily necessary when a pilot requires an alerting service. This is important because flight plans help air traffic services to be aware of an aircraft's intended flight route and can assist in search and rescue operations if needed. An alerting service is crucial in situations where a pilot may experience difficulties, as it allows for a quicker response by search and rescue teams if the aircraft does not arrive at its planned destination as expected.

While flying close to shore, operating under certain types of air traffic operations (ATOs), or during daytime local flights might give pilots more flexibility regarding flight plans, they do not comprehensively necessitate the filing of one. The requirement for a flight plan is primarily tied to the need for monitoring and assistance, as described in the context of requiring an alerting service. This framework emphasizes safety and situational awareness in aviation operations.