IOWA CITY — The Federal Aviation Administration is investigating what caused a $300,000 research drone owned by the University of Iowa to crash Dec. 18, leaving a fiery wreck in a densely packed mobile home park near the Iowa City Airport.The Latitude HQ90B, a 100-pound drone with an 18-foot wingspan, “became unresponsive” during the afternoon flight and crashed in a yard at the Lake Ridge mobile home park, the UI reported.