What essential documents must be on board an aircraft?

The essential documents that must be on board an aircraft include the airworthiness certificate, registration, and weight/balance information. The airworthiness certificate is a critical document that indicates the aircraft is in a condition for safe operation and complies with the Federal Aviation Administration (FAA) regulations. The registration serves to establish ownership and verifies that the aircraft is legally recognized to operate in the airspace. Weight and balance information is crucial for ensuring that the aircraft operates within its operational limits, which directly affects safety and performance during flight.

While other documents such as flight logs and maintenance records are important for operational procedures and tracking, they are not mandated to be present on board for every flight in the same way as the airworthiness certificate, registration, and weight/balance documentation are. This makes option B the correct understanding of the requirements for essential documents on board an aircraft.