At 1529 eastern time, a Piper PA-46-310P crashed while trying to return to the airport shortly after takeoff from Hilton Head Airport. The pilot and passenger were killed. The pilot took off and, four minutes later, declared an emergency on the airports common traffic advisory frequency. The pilot said he was making an immediate return. One witness heard the CTAF broadcast mention something about a cover off and said the airplane was trailing what appeared to be smoke from the left wing tip only. Initial examination of the airplane, which was modified to use a turboprop engine, showed the left inboard fuel cap was missing. It was found in the grass beside the departure runway.