Several space-based augmentation systems have been developed recently to augment Global Navigation Satellite System (GNSS) services for enhanced air navigation performance. In Asian Pacific region, the Japanese Multi-functional Satellite Augmentation System (MSAS) has been commissioned recently to broadcast Global Positioning System (GPS)augmentation information for aviation. The Taipei Flight Information Region (FIR) is located on the border of the MSAS service volume, it is thus of technical and operational interests to assess the performance of MSAS in Taipei FIR so as to pave a way for the future Space-Based Augmentation System (SBAS) implementation. In the paper, data analysis results of the received MSAS messages during a period of more than two months are reported in terms of the Required Navigation Performance (RNP)at different phases of flight. It is found that the requirement of Non-Precision Approach (NPA) can be met while the Precision Approach (PA) mode is subject to availability and integrity issues with the existing MSAS data and SBAS procedure. An adaptive weighting strategy is proposed so that the spatial difference of GPS satellites between the Taipei FIR and MSAS service volume can be better accounted for. By using the adaptive weighting strategy, the PA required navigation performance can be achieved in Taipei FIR with an availability of 99.999% based on the analysis of collected data.