The pilots of the rented twin-engine Piper Apache reported the fuel tanks were half full when the right engine stopped — followed a few minutes later by the left engine — forcing a ditching in the ocean off Kona last month, according to a preliminary report by the National Transportation Safety Board.

The NTSB report, released last week, said pilots David McMahon, 26, of Kailua and Sydnie Uemoto, 24, of Kona were cruising at 5,500 feet on July 14 when both engines began to run rough.

They descended to 3,500 feet, and the engines seemed to smooth out a bit.

Then the right engine stopped producing power, followed within a few minutes by the left engine, the report said. The pilots reported that the fuel gauges were showing half full.

The pilots reported engine trouble shortly before 3:15 p.m. and lost radio contact with the airport control tower before ditching the plane, the Coast Guard and Federal Aviation Administration reported. Their last known location before disappearing from the radar was 25 miles northwest of Kona Airport.

After spending a night in the ocean, the two off-duty commercial pilots with Mokulele Airlines were found July 15 trying to swim the last mile and a half to shore.

The airplane sank and was not recovered.

The flight had left John Rodgers Airport at Kapolei and was en route to Kona.

A tour helicopter pilot spotted the debris and the survivors 1.5 miles offshore, 6 miles northwest of Kona Airport. That pilot contacted a nearby Coast Guard helicopter, which remained on scene until another Coast Guard helicopter with hoisting capabilities arrived, hoisted up the pair and flew them to Kona Airport, where they were treated for minor injuries.

Participating in the search were private tour helicopters, the Navy, a New Zealand air force P-3 Orion plane participating in the Rim of the Pacific military exercises, and the Hawaii County Fire Department.