Aircraft's position in three dimensions from at least 4 available satellites and one on-board inertial system.

Accuracy of the computed aircraft position based on input from at least one ground-based radio transmitter.

Predicted positions of GNSS satellites to ensure that the required Geometric Dilution Of Precision (GDOP) willbe available at all times.

Integrity of the GNSS navigation signals using only GPS signals or GPS signals augmented with altitude.