BeiDou Navigation Satellite System (hereinafter referred to as BDS) has started the Standards and Recommended Practices(SARPs) development in International Civil aviation Organization (ICAO) since 2011 and successfully completed BDS SARPs validation work at NSP/6 meeting in November 2020. As the main BDS Open Service signals intended for civil aviation use, B1C and B2a signals are the main concern for civil aviation airborne receiver manufactures. The main goal of the paper is to provide the analysis of the post correlation carrier-to-noise ratio threshold required by the acquisition, tracking and data demodulation for B1C and B2a signals of BDS, which can be used to support the standardization of B1C and B2a signals in ICAO. The analysis methodology adopted in this paper refers to the analysis framework of GPS L1C/A signal in RTCA DO235B  and GPS L5 signal in RTCA DO292 . The paper first gives an overview of BDS B1C and BDS B2a signals characteristics such as center frequency, modulation, power sharing, primary/secondary code lengths and FEC scheme. Then following three sections are the analysis of acquisition, tracking and data demodulation threshold. In the acquisition threshold section, a simple acquisition algorithm is considered. The acquisition threshold is calculated based on the false alarm probability, the acquisition probability, and the number of incoherent accumulations. In the tracking threshold section, after considering tracking jitters and tracking deviation caused by dynamic stress, the relationship between cycle slip rate and the carrier-to-noise ratio is determined, so that the tracking C/N0 threshold can be given according to the cycle slip rate requirements. In the data demodulation section, the threshold is determined by the Bit Error Rate (BER) and Frame Error Rate (FER) requirements, and the results are given directly through simulation, for there is no general theoretical formula for the decoding performance of 64-ary LDPC coding.