Patty Wagstaff is the first woman to earn the title of U.S. National Aerobatic Champion.[163] Latifa Nabizada and her sister Lailuma graduate from helicopter flight school and become Afghanistan's first women pilots.[164] Beverley Drake of Guyana was the first female accident investigator of the U.S. National Transportation Safety Board.[138] The first Canadian Women in Aviation Conference is held. The conferences are held every two years by volunteers.[165] July 31: The United States Senate voted "overwhelmingly" to allow American military women to fly aircraft in combat situations.[166]