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

The ability to execute an approach largely depends on visibility conditions, as this directly affects a pilot's capability to see the runway and surrounding environment during landing. Poor visibility can arise from fog, rain, or other weather phenomena, making it unsafe or impossible for a pilot to land the aircraft visually.

While air traffic control clearance, weather conditions, and aircraft performance are all significant factors in flight operations, they do not solely govern the execution of an approach in the same manner that visibility does. Without adequate visibility, even with clearance and optimal aircraft performance, a pilot may not be able to safely conduct the approach and landing. Therefore, visibility serves as the critical controlling factor in ensuring that the approach can be executed safely.