What is required from the captain during line checks?

The requirement for the captain to have at least one random, no-notice line check every 18 months is a critical measure to ensure consistent operational standards and safety compliance. This type of check is designed to assess the captain's performance in a real-world environment without prior notice, which simulates actual flight operations and ensures that the captain is always prepared to adhere to procedures and protocols.

This process helps maintain a high level of operational oversight and accountability. The emphasis on random checks also serves as a motivator for captains to remain vigilant and proficient in their duties, as they recognize that their proficiency will be evaluated at any time within the defined period.

While the other choices mentioned might involve important aspects of flight operations, they do not align with the specific regulatory requirements regarding line checks for captains.