(b) If the contractor can establish, or it is otherwise determined that the contractor was not in default or that the failure to perform is excusable; i.e., arose out of causes beyond the control and without the fault or negligence of the contractor, the default clauses prescribed in 49.503 and located at 52.249 provide that a termination for default will be considered to have been a termination for the convenience of the Government, and the rights and obligations of the parties governed accordingly.