Results in support of the ICAO GRAS validation test

As part of the ICAO navigation systems panel ground-based regional augmentation system (GRAS) validation process, issues arose concerning the transition between VHF data broadcast (VDB) stations. The GRAS sub group was invited to demonstrate that hand-over occurs only after successful lock onto a new VDB after 60 seconds of tracking the new power level and that the use of the new data does not affect the availability, accuracy, and continuity of service. Airservices Australia was invited to provide a description/depiction of receiver power; position accuracy referenced to the truth system, and the horizontal protection error (HPE) and vertical protection error (VPE) on hand-over scenario. This paper shows results from 73 transitions and demonstrates that the change between VDB stations does not affect the availability, accuracy, or continuity of service. Additionally, an evaluation was made on the effects of spatial decorrelation on the GRAS broadcast message when broadcast from a site geographically displaced from a reference station. The results show that GRAS remains well within the horizontal and vertical alarm limits prescribed for approaches with vertical guidance (APV).