SIX people, including the group chief executive of one of Nigeria's largest banks, were killed in a helicopter crash in Southern California, authorities and the banking group said. Six people were on board the helicopter when it crashed around 10 p.m. Friday (0600 GMT Saturday) near Nipton, California, the U.S. Federal Aviation Administration said in a statement. Access Holdings said its CEO Herbert Wigwe, his wife and son were among those who died in the crash. "We extend our deep and sincere sympathies to his family and loved ones," Access Holdings Chairman Abubakar Jimoh said in a statement on Sunday,…