PORTLAND – Federal officials are investigating the cause of a helicopter crash that claimed the lives of two Portland women who were vacationing together in Hawaii.

Mary Soucy, 62, and Catherine Baron, 68, were aboard the sightseeing helicopter when it went down in the Pacific on Friday during a sudden storm. A third passenger was killed and three other occupants of the chopper were able to escape the wreckage and swim to a nearby reef.

Both widowed, Baron and Soucy were best friends. Baron had retired this summer from her job as an administrator at the University of Southern Maine’s Muskie Center; Soucy worked at Deering Pavilion, a housing complex for the elderly in Portland.

National Transportation Safety Board officials are investigating the crash and will try to determine how much weather, mechanical problems or human factors were to blame. The storm triggered lightning, strong winds and heavy rainfall as the Eurocopter AS-350 operated by Heli-USA was flying near the rugged Na Pali coast of the island of Kauai.

Baron and Soucy had spent the past two weeks touring the Hawaiian Islands, and the helicopter trip likely was to be a final highlight of their trip, said Baron’s son-in-law Mark Philbrick.

“Cathy had worked hard and long at the Muskie School in order to be able to retire to focus on her grandchildren, gardening and traveling, and this was her first trip with her best friend after her retirement,” Philbrick said. “They were near the end of their second week of vacation in Hawaii and taking that stupid helicopter trip was kind of a highlight … People are really going to miss her.”

The fatal helicopter crash was the second in a year in the area. In the earlier incident, a helicopter on a sightseeing trip crashed into a ridge killing the five people on board.

A spokesman for the National Transportation Safety Board said a preliminary report on the accident should be complete in a week to 10 days. A more detailed report and a determination of the cause of the accident will likely take months once the wreckage is studied, maintenance records reviewed and weather conditions analyzed, the spokesman said.