Why shouldn't you join an approach at an intermediate fix?

Joining an approach at an intermediate fix primarily raises concerns about assuring obstacle clearance. When a pilot starts an approach from an intermediate point rather than the intended initial approach fix (IAF), there might be terrain or obstacles that are not adequately accounted for on the flight path, as the standard procedure has not been followed.

Approaches are designed with specific altitudes and lateral paths to ensure safety and compliance with obstacle clearance requirements. These procedures provide critical information regarding safe altitudes and necessary waypoints throughout the approach. In contrast, entering the approach at an intermediate fix skips essential segments that are intended to help pilots navigate safely and maintain situational awareness regarding nearby obstacles. The absence of this guidance could potentially lead to unsafe conditions, particularly if the pilot assumes a level of clearance where it may not exist.

Other options provide different perspectives but do not fully capture the safety concerns validated by aviation regulations and best practices associated with obstacle clearance.