Aircraft navigation requires better accuracy, availability and integrity than GPS alone can provide now and in the next few years. Augmentation systems like SBAS and GBAS greatly improve accuracy and integrity locally or in one part of the world. Taken together GPS, GLONASS and Galileo will perform with much better accuracy, availability and integrity with global coverage and are capable to compensate potential constellation gaps in one of the GNSS.

Nowadays GPS receivers became a synonym for precise time and frequency.
This paper will show that this is - in a wide range - true, but a lot oft different aspects have to be thought of. It talks about expectations and achievable accuracy, stability and precision and a few measures that have to be taken in order to achieve what is to be achieved.

Time: Date, Duration, and Synchronisation

COORDINATED UNIVERSAL TIME (UTC)

GPS TIME