HALF MOON BAY, Calif. (AP) — Investigators are looking into the possibility that fuel issues may have caused a small plane to crash into the Pacific Ocean, killing two people on board.

The Viking Air DHC-6-400 Twin Otter was equipped with an additional fuel system that would have allowed it to go further than it could with its original fuel tanks, said Sarah Sulick, a spokesperson for the National Transportation Safety Board.

“According to reports, they were having problems with their fuel, so investigators want to look at the issue of ‘fuel starvation,’ which would mean there was a problem with ferry tanks supplying enough fuel to the main tanks,” she said.

The small plane crashed around 2:15 p.m. Saturday about 40 miles off the coast of Half Moon Bay, California. The turboprop aircraft was en route from Santa Rosa, in Sonoma County north of San Francisco, to Honolulu, Hawaii, federal authorities have said.

The U.S. Coast Guard found the submerged plane and confirmed the pilot and copilot were dead. They were the only people on board, officials said. Their names have not been released.

Crews are working to recover the wreckage.

Half Moon Bay is a coastal community about 20 miles (32 km) south of San Francisco.