Two crew members were killed and two others were missing Thursday after a US Navy helicopter crashed in the Gulf of Mexico. Two others were recovering from injuries. The survivors, found floating with inflatable life jackets, were rescued more than 30 minutes after the helicopter went down. They were in stable condition at a hospital in Corpus Christi, said a lieutenant with Naval Air Station Corpus Christi. Several Coast Guard and Navy craft were searching for the missing crew members Thursday afternoon. The crew was aboard an MH-53E helicopter, also known as a Sea Dragon, that was practicing minesweeping when it crashed about 11 a.m. about 17 miles offshore. Crew members reported mechanical problems and the helicopter was attempting to return to shore when it crashed, said a commander at the naval air station.