NTSB: Pilot killed in Anchorage crash had carbon monoxide in system

An examination of the pilot who died in the fiery crash of his home-built floatplane on the Anchorage Hillside in September found that he had significant levels of a carbon monoxide in his body, apparently from failures in the plane's exhaust system.

James Hefty, 75, was at the controls of the experimental Polar Cub that crashed on Crooked Tree Drive at about 4:30 p.m. Sept. 10. The National Transportation Safety Board released the results of autopsy and toxicology work, including the presence of the disorienting gas, in a docket of materials supporting a factual report on the crash Tuesday.

The plane took off from Jewel Lake in Anchorage at about 3 p.m. on a day with few clouds in the sky, according to the report. Numerous witnesses to the crash told the NTSB that Hefty made two high-speed turns over the Hillside at altitudes as low as 50 feet. Shortly afterward, his plane hit trees near a home, struck the road upside-down and burned.

Hefty's most recent medical certificate allowing him to fly, issued in 2007 by the Federal Aviation Administration, included a number of medical restrictions and indicated it was not valid after May 31, 2008. But Clint Johnson, the NTSB's Alaska chief, said Hefty had disassembled the plane, originally a Piper PA-11, and reconstructed it as an amateur-built aircraft — allowing him to fly it with only a driver's license.

Johnson, who acted as the lead investigator on the Hillside crash, said Alaska has a growing amateur-built aircraft scene, although the category isn't as popular here as it is in the Lower 48.

"There's less regulation," Johnson said. "There's a lot of advantages, but there's also some restrictions — you can't use the airplane for charter (flights)."

Tests revealed a 48 percent saturation of carbon monoxide in Hefty's blood. Medical staff with the NTSB said in their findings that nonsmokers like Hefty have ambient CO levels of 3 percent; levels from 10 to 20 percent can result in "confusion, impaired judgment, and difficulty concentrating."

That level of carbon monoxide in Hefty's body was an apparent factor, Johnson said, in the turns people saw his plane make before it crashed.

"We don't know what the level of impairment was, but you can see — just looking at the facts, just looking at the obvious facts — there was either partial impairment or something that obviously degraded the pilot's performance here," Johnson said.

Johnson said the autopsy and toxicology reports prompted a closer look at the plane's exhaust system, which revealed previous damage including holes in the muffler. A 2007 FAA advisory warns pilots that exhaust gases can enter the cabin from damaged mufflers or exhaust systems, which are often used to heat cabin air.

A full examination of the muffler by the NTSB's laboratory in Washington, D.C., ruled out impact or fire as the cause of its degradation, Johnson said. In an overview of the inspection, NTSB scientists said that a piece of metal from a damaged section of the muffler can was brittle enough to be fractured into smaller pieces "with little force applied by hand."

"If you look at the damage on that muffler, that's not something that happened on that 90-minute flight," Johnson said. "They were able to determine that the muffler system or muffler can was degraded to a point where it allowed raw exhaust gases to enter the cabin."

Hefty was responsible for the Polar Cub's maintenance, but Johnson said the NTSB wasn't able to find maintenance logbooks for the plane. Hefty's family and friends said those records were likely on board the aircraft when it crashed, according to the report.

The original source of the muffler damage wasn't clear, Johnson said, but the damage would have been discovered during an annual aircraft inspection.

"This is one of the elementary things you look at," Johnson said. "You pop that thing open, take a look at it, make sure it has no holes in it."

Carbon monoxide poisoning was discovered in another fatal Alaska crash the year before Hefty's, a May 2015 Yute Air maintenance flight that killed 47-year-old pilot Blaze Highlander. NTSB investigators weren't sure exactly how Highlander's blood received a 21 percent saturation of CO before the Cessna 207 crashed into the Kwethluk River, but noted in September that it "did come from the airplane."

A probable cause for the Hillside crash will likely be determined within the next few weeks, Johnson said.