During what time frame does a Calendar Day begin and end?

The definition of a calendar day in the context of flight operations typically spans from 0000 to 2359, which aligns with the 24-hour clock system used by aviation. This time frame indicates that a calendar day begins at midnight (00:00) and concludes just before the next midnight (23:59), effectively allowing for the full spectrum of time within that specific day to be accounted for in schedules, duty rosters, and operational loggings.

Selecting the range of 0001 to 2400 is slightly misleading, as the latter could suggest an entire hour extending into an ambiguous timeframe beyond that day. Additionally, the use of '2400' is often discouraged in standard aviation terminology because it can create confusion with the beginning of the next day; rather, the endpoint should always be noted as 2359 to clear any potential misunderstandings regarding the timing.

The other answers do not reflect this commonly accepted definition, as the notion of a day varying by airline policy creates unnecessary ambiguity and doesn't establish a uniform standard across the industry. Understanding this clear demarcation of time is crucial for flight attendants and aviation professionals to manage their schedules, ensure compliance with duty regulations, and maintain safety and organizational standards within their operations.