What does 'aircraft downtime' refer to?

Aircraft downtime refers to the period during which an aircraft is not operational due to maintenance. This could include scheduled maintenance checks, repairs, inspections, or any unexpected issues that require the aircraft to be taken out of service. Understanding this concept is crucial for managing an airline’s operational efficiency and ensuring safety standards, as aircraft must be maintained regularly to remain airworthy.

The other options do not accurately capture the definition of downtime. For instance, the period when an aircraft is in the air describes operational time, while the planned flight duration pertains to how long a flight is expected to last after takeoff. The time taken for preflight inspections refers to a specific activity conducted before a flight, but does not encompass the broader concept of aircraft being non-operational due to maintenance. Therefore, option B correctly defines aircraft downtime as it directly addresses the lack of operational capability resulting from maintenance activities.