What constitutes a deviation from ATC clearance that the pilot must report?

A deviation from ATC clearance occurs when the pilot does not follow the instructions provided by air traffic control. This can involve alterations to altitude, heading, or route that are not in accordance with the clearance received.

When a pilot makes an unauthorized altitude change, this is significant because it alters the aircraft's flight profile, potentially leading to conflicts with other aircraft or violating controlled airspace regulations. The requirement to report this deviation is critical for maintaining safety and communication in the airspace system.

Other factors like minor altitude fluctuations, non-standard approach speeds, or temporary loss of communication do not necessarily constitute a deviation from an ATC clearance that requires immediate reporting. Minor fluctuations may occur during normal flight without impacting safety or ATC compliance, while managing approach speeds typically falls within the discretion of the pilot unless otherwise specified by ATC. Loss of communication may require follow-up actions, but the pilot's responsibilities regarding clearance deviations are separate from communication issues.