# Construction Progress and Aviation Flight Test of BDSBAS
## 5 Conclusions  
In this paper, we described the overall situation and the construction progress of China's BDSBAS, and used the general aviation aircraft to carry out the flight test at Shenyang Caihu Airport. The BDSBAS SF service performance is evaluated and analyzed in terms of positioning accuracy, availability, continuity, and integrity.  
In the flight test carried out on 17 September 2020, the take-off and landing operation was simulated with a horizontal positioning accuracy of 1.62 m (95%) and a vertical positioning accuracy of 4.38 m (95%). In the flight test carried out on 18 September, the take-off and landing operation and the great-circle flight operation were simulated with a horizontal positioning accuracy of 1.27 m (95%) and a vertical positioning accuracy of 4.30 m (95%). For these two tests, the APV-I availability and continuity of the BDSBAS SF service reach 100%.  
In the flight test carried out on 25 September, the transition flight operation was simulated, with a horizontal positioning accuracy of 1.49 m (95%) and a vertical positioning accuracy of 4.04 m (95%). However, due to the false alarm event during the test, the APV-I availability and the continuity did not reach 100% but 99.993% and 99.989%, respectively. By comparing with the data of the ground MSs, we found that there were no abnormalities in the BDSBAS service during the same period. Therefore, we believe that this false alarm event was caused by some environmental factors such as the aviation electromagnetic interference.  
The vertical accuracy of each flight test was approximately 4 m, which was due to the following reasons: (1) In September 2020, BDSBAS was in the initial testing stage, and the accuracy of orbit-clock corrections and ionospheric correction still needed to be further optimized; (2) The test location was at Shenyang, which is at the verge of BDSBAS service area. The Civil Aviation Administration of China (CAAC) will carry out the certification of  
Figure 25: Number of augmented GPS satellites available for BDSBAS MSs.  
the BDSBAS SF service. Currently, the certification plan has been completed and approved. The whole certification work will include three areas: a system technical review, service performance monitoring, and a flight operation test (which are expected to be completed in three to four years). In future, we will continue to conduct aviation tests covering more operations in order to more fully analyze and evaluate the performance of BDSBAS, including its ability to serve marginal areas. With the completion of the certification process, CAAC will approve the BDSBAS SF service to serve aviation users.  
Conceptualization, W.G.; original draft preparation, C.L.; methodology, Y.C. and J.L.; data analysis, B.S.; data curation and supervision, C.S.; project administration, S.X. All authors have read and agreed to the published version of the manuscript.  
This work was supported in part by the National Natural Science Foundation of China (Grant Nos. 42074044 and 41974041) and in part by the Young Elite Scientist Sponsorship Program by CAST (Grant No. 2019 QNRC001).  
Not applicable.  
The authors declare no conflict of interest.