Which document is essential for validating the pilot's capability to operate the aircraft?

The essential document for validating a pilot's capability to operate an aircraft is the pilot license. A pilot license demonstrates that the individual has completed the necessary training and has successfully passed the required exams to be certified to fly. It specifies the type of aircraft the pilot is authorized to operate and ensures that they meet the regulatory standards set by aviation authorities.

While medical certificates are important for verifying a pilot's health and fitness to fly, they do not validate the pilot's ability to operate an aircraft or their level of training. Flight logs serve as records of a pilot's flying experience but do not intrinsically validate flying capability on their own; they are more of a tracking tool. Aircraft registration pertains to the ownership and identification of the aircraft, rather than the qualifications of the pilot. Thus, the pilot license is the definitive credential that confirms a pilot's training and capability to operate a specific type of aircraft.