Modern Air Traffic Control CNS (Central Navigation Systems) use clusters operating in UTC time domain. It is requiring robust synchronization accuracy better than a millisecond. For an airplane flying at a speed of about 1000 km/h, the synchronization ERROR of 1s defines a position error of 300 meters. A Voice Control Systems (VCS) require trusted timestamping to store pilot voice and telemetry flight data, proving event chronology and nonrepudiation. A UTC leap second support is essential for CNS.