How is flight duration measured in ATP aircraft?

Flight duration in ATP aircraft is typically measured using the "OFF/ON" hour meter. This instrument records the time that the aircraft's engines are operating, providing a clear and accurate measure of flight time that can be relied upon for flight logs, maintenance schedules, and operations compliance.

The "OFF/ON" hour meter is directly linked to the aircraft's operating systems, making it a robust tool for tracking actual flight time from engine start (ON) to engine shutdown (OFF). As a result, it serves a dual purpose: it aids pilots in managing flight time and helps maintain the aircraft by ensuring maintenance is scheduled based on actual usage.

While GPS timers, flight logs, and chronometers can also track time, they may not provide the same level of precision and reliability in measuring operational flight duration as the "OFF/ON" hour meter. GPS timers can be influenced by signal loss or errors, flight logs depend on manual entries which could be inconsistent, and chronometers require manual activation and deactivation, making them less reliable for official measurement purposes in aviation operations.