What is the controlling factor for whether an approach can be executed?

The controlling factor for whether an approach can be executed is visibility. Visibility directly impacts a pilot's ability to safely execute an approach and landing. If visibility is below the minimums specified for the approach being used, the approach cannot be legally or safely conducted.

Pilots must be able to see the runway environment during the final stages of an approach to ensure a safe landing, and reduced visibility can compromise this ability. This is particularly critical during low visibility situations such as fog, rain, or during nighttime operations where visual references are limited.

While air traffic control clearance is essential for managing air traffic and ensuring safe separation between aircraft, it is still possible to receive clearance but be unable to execute the approach due to poor visibility. Weather conditions overall affect approach execution, but visibility is a more specific determining factor. Aircraft performance can certainly influence the ability to execute an approach, particularly in challenging conditions, but first and foremost, visibility must meet the necessary criteria for safe operations.