South Carolina ? A medical helicopter that crashed in coastal South Carolina, killing all three crew members on board, had run into bad weather and was trying to land at a nearby airport, federal safety investigators said Saturday.

The helicopter had just dropped off a patient at a hospital in Charleston and was flying to Conway, about 90 miles to the northeast, when it crashed late Friday in Georgetown County, said Peter Knudson, a spokesman for the National Transportation Safety Board.

A thunderstorm had rolled through the Georgetown area shortly before the crash, according to the National Weather Service.

Robert Sumwalt, an NTSB member, said the crew had reported to its company, Texas-based OmniFlight, that they were trying to land.