Simulations are conducted in time domain to investigate the transient response of a SPAR-type floating offshore wind turbine in scenarios with fractured mooring lines. Towards this end, a coupled aero-hydro-elastic numerical model is developed. The methodology includes a blade-element-momentum model for aerodynamics, a nonlinear model for hydrodynamics, a nonlinear restoring model of SPAR buoy, and a fully nonlinear dynamic algorithm for intact and fractured mooring cables. The OC3 Hywind SPAR-type FOWT is chosen as an example to study the dynamic response after one of its mooring lines is suddenly broken. The motions of platform, the tensions in the mooring lines and the power generation performance are documented in different cases, including different fractured cables and different shutdown strategies. An interesting finding is that in terms of drift distance, it might be more dangerous to shut down the turbine in certain scenarios. Furthermore, the potential impacts of mooring failure on adjacent FOWTs are discussed for two designs of the wind farm. (C) 2018 Elsevier Ltd. All rights reserved.