The exploitation of GNSS time as a reference source for timing and synchronisation processes is becoming fundamental for critical infrastructures like telecommunication networks, energy distribution grids, financial markets, and commercial aviation systems and networks.
In the case of commercial aviation, GNSS time is used for:

• Positioning and timing for on-board navigation purposes;
• Timing and synchronisation for datalink communications (on-board to ground and vice-versa);
• Timing and synchronisation for ground systems used for Air Traffic Control (ATC), communication networks, airspace surveillance,      and airport logistics coordination.

GNSS time is an integral part of GNSS services, it becomes unreliable or unavailable when GNSS system outages or signal anomalies occur. Nevertheless, dependency on GNSS for Communication, Navigation and Surveillance (CNS) systems is expected to increase. More and more aircraft are being equipped with systems like ADS-B, SBAS, and GBAS that depend on GNSS being available. For some aircraft classes GNSS is the only navigation equipment required to fly under Instrument Flight Rules (IFR) and no alternative means of navigation may be available on-board.
The Single European Sky ATM Research (SESAR) Joint Undertaking is introducing high-performance aviation for Europe through trajectory-based operations by defining, developing and delivering new or improved technologies and procedures, and allowing for the ground infrastructure to be rationalised. GNSS is the key technology to achieve these objectives and will become the primary means of aircraft navigation in the mid and long term.
At the same time, other and independent timing sources may be available to backup or complement the GNSS timing and synchronisation service, e.g. atomic clocks, Low Frequency systems, Network Time Protocols (NTPs). Their suitability for usage may depend on various factors, including coverage area, phase of flight, and performance requirements of ground equipment for surveillance and communications.

The objectives of this project are to:

• Assess the criticality of the use of GNSS time in aviation;
• Define and perform demonstration of innovative timing concepts complementary to GNSS, in order to provide robust and secure       timing and synchronisation services for aviation systems and networks.
• Provide recommendations to aviation stakeholders (CNS/ATM) to support their progress towards a safer Air Traffic Control.