A Coast Guard helicopter made an emergency landing Sunday during a rescue operation for an ailing mariner.

The MH-65 Dolphin helicopter received an alarm about a tail gearbox malfunction while lowering a rescue swimmer onto the container ship Kachidoki Bridge about 35 miles off Oahu.

The helicopter crew returned to Oahu and made an emergency landing at Dillingham Airfield at about 11 a.m., said Coast Guard Petty Officer 3rd Class Amanda Levasseur. No injuries were reported, and the Coast Guard planned to assess the helicopter and make repairs.

A second dolphin helicopter was launched from Coast Guard Air Station Barbers Point and picked up the 31-year-old crewman, who was complaining of severe abdominal pain. He was taken to the Queen’s Medical Center for treatment.

The Portuguese-flagged vessel was en route to Los Angeles when its crew contacted the Coast Guard about 8:30 p.m. Friday, asking for help transporting the man for medical treatment. The vessel was 983 miles north of Oahu at the time, and a Coast Guard flight surgeon did not recommend an immediate rescue, but recommended the vessel make best course and speed toward Oahu, the Coast Guard said.

The Coast Guard first launched the dolphin helicopter to pick up the man about 10 a.m. Sunday.