Wreckage lost at sea made the mechanical cause of the single-engine airplane that crashed into Lynn Canal during the fall of 2016 impossible to determine, according to a National Transportation Safety Board final accident report released last week.

The probable cause of the crash was, “a loss of engine power due to fuel exhaustion for reasons that could not be determined based on available evidence and the pilot’s decision to continue the flight after realizing the remaining fuel quantity was near zero,” the report says.

Pilot Mike Mackowiak was on the return leg of a round-trip flight from Haines to Juneau during the Nov. 4, 2016 crash.

He was about 20 miles northwest of Juneau into the flight to Haines when he noticed both fuel gauges at zero.

With full fuel tanks, the plane burned about 12 gallons during the trip from Haines to Juneau, leaving around 53 gallons of fuel remaining in the tanks for the return journey, Mackowiak told NTSB investigators.

“The distance between Juneau and Haines is about 66 nautical miles, and the estimated flight time was about one hour,” the report states. “The estimated fuel remaining once the flight reached its final destination of Haines would have been about 41 gallons.”

“During the climb (toward Haines), he tapped on the face of the fuel gauges and the indication on the right gauge increased between one-fourth and three-eighths,” the report says. “(Mackowiak) said that he was convinced that the erroneous fuel quantity indication was due to an electrical malfunction, so he elected to continue to Haines.”

As he flew closer to Haines the engine lost all power and Mackowiak couldn’t restart it.

Mackowiak, his wife Martha, son Nik and family friend Victoria Hansen survived the accident after landing around 23 miles southeast of Haines in Lynn Canal. The aircraft nosed over in the water and the passengers climbed out of the plane and stood on the wing before it sank.

They swam to shore where a U.S. Coast Guard helicopter later rescued them. They were transported to medical facilities where they received treatment for hypothermia.

The plane’s wreckage sank beneath an estimated 600 to 780 feet of water at the time of the accident and could not be recovered, making a wreckage examination of the fuel system impossible.