What must pilots do whenever a flight change necessitates deviations from their flight plan?

When a flight change requires deviations from an established flight plan, pilots are required to notify air traffic control (ATC). This is essential for maintaining safety and ensuring the efficient flow of air traffic. By informing ATC, pilots provide the necessary information that allows controllers to manage the airspace effectively and keep other aircraft informed of any changes. Deviation from a flight plan could be due to various reasons, such as changes in weather, emergencies, or altered flight conditions, and only through communication with ATC can pilots ensure they remain in compliance with regulations and operational standards.

In this context, the other choices do not align with the requirements. Landing the aircraft immediately is not always necessary unless there is a critical situation. Adjusting altitude solely to match other aircraft does not apply unless directed by ATC or needed for separation; changes to altitude should still be communicated to ATC. Filing a new flight plan in advance is not always feasible, especially for real-time changes; instead, communicating deviations immediately is more critical for safety and operational efficiency.