Impact of Tropospheric Anomalies on GBAS Integrity

Ground-based augmentation systems (GBAS) improve the positioning accuracy of aircraft through differential correction techniques during the approach process and enable aircraft to achieve higher services through various monitoring algorithms. Many errors need to be eliminated during navigation. Tropospheric delay is one of the most critical errors in a GBAS. Under normal atmospheric conditions, most of the tropospheric delays can be eliminated by using the difference method and TC model. However, these methods are not applicable under anomalous atmospheric conditions, and abnormal atmospheric conditions have been observed by both the International Civil Aviation Organization (ICAO) and Single European Sky Air Traffic Management Research (SESAR). Anomalous atmospheric conditions pose a great threat to aircraft safety. An integrity monitoring approach may be taken, or the threat may be incorporated into the normal model and overbounded by the protection levels. This paper focuses on non-nominal anomalies in different regions and in different seasons. We found that the maximum residual tropospheric delay caused by non-nominal anomalies exceeds 35 cm. In addition, the frequency of and the maximum residual tropospheric delay caused by the simultaneous occurrence of duct anomalies and non-nominal anomalies are studied here. We found that the maximum frequency of non-nominal and duct anomalies occurring simultaneously exceeds 70%. Finally, this paper used the previously developed overbound method to overbound the two kinds of tropospheric anomalies using data from Dongying Airport. We found that the impact of duct anomalies on the protection levels is greater than that of non-nominal anomalies at Dongying Airport.