The tragic crash of a helicopter that killed six people, including top Nigerian banker Herbert Wigwe and his family, in the U.S. could have been avoided due to the weather conditions, according to U.S. aviation attorney Robert A. Clifford. In an exclusive interview with Business Insider Africa, Clifford, describes what the National Transportation Safety Board is investigating to determine the cause of the helicopter crash. Clifford is the lead counsel in a court case against Boeing for the crash in Ethiopia of a Boeing 737 Max 8 that killed 157 persons from 35 nations, including 56 passengers …