The emergence of broadband wireless access technologies enables seamless Internet access in mobile environments. To fully utilize the broadband wireless bandwidth, it is critical to design a congestion control mechanism that can adjust the congestion window size according to the dynamics of the wireless network condition. A congestion window size that does not react properly to the degradation of channel quality injects excessive data segments into the network. This increases round trip time (RTT) and ultimately may cause packet losses. In the reverse setting, when the channel quality improves drastically, the congestion window should react fast enough to take advantage of the available bandwidth. This paper proposes Flight Size Auto Tuning (FSAT) as a new TCP variant. FS-AT adjusts the transmission rate according to the estimated available throughput and fluctuations in throughput to mitigate the network congestion while maintaining high network utilization. Moreover, FS-AT provides mechanisms to differentiate between the losses caused by channel errors and those by network congestion. Accordingly, the proposed method avoids unnecessary throughput reduction in case of channel errors, a well-known impediment of standard TCP schemes. FS-AT estimates the current available bandwidth from the received acknowledgments without requiring any modification at the receiver. FS-AT is implemented on Linux and the effectiveness of FS-AT is validated by the measured performance of FS-AT over HSDPA and the simulated performance over a fixed network.