As mobile devices grew rapidly over the past few years, the wireless data demand has increased exponentially. Due to the extremely high price of licensed spectrum, License Assisted Access (LAA) has been proposed to provide high capacity by extending LTE transmissions to the unlicensed spectrum that WiFi systems operate. Due to the coexistence with WiFi systems, mobility management has become a critical problem in LTE-LAA networks. Compared with handover in traditional LTE networks that would only be triggered by user mobility in licensed bands, in LTE-LAA networks, handover can also be triggered due to the unavailability of unlicensed band in the serving cell. In this paper, a new handover scheme is proposed and analyzed in details for LTE-LAA networks, including handover triggering and handover procedure. We perform simulation to evaluate the performance of our proposed handover scheme with availability triggered handover considered. The simulation results show that by introducing availability triggered handover, the unlicensed spectrum handover ratio has a significant improvement, meaning that a more efficient utilization of unlicensed spectrum can be achieved, while the handover failure rate will relatively increase as compared with the traditional handover scheme.