June 18, 2018
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‘Fatigue failure’ in 65-year-old engine part caused Durham doctor’s fatal plane crash

By Terry Karkos, Sun Journal

Fatigue failure of an engine part that was more than 65 years old caused a Durham doctor to fatally ditch his antique plane in the ocean near Portland Head Light in Cape Elizabeth last summer.

The 1946 Stinson Voyager was flying over the ocean along the coast on June 24 at altitudes between 500 and 1,000 feet when Louis Hanson reported a total loss of engine power. He indicated he couldn’t glide to the shore.

The Voyager subsequently impacted water about 100 yards from the shore and sank to a depth of about 70 feet.

Just before noon that day, Hanson, 60, was pulled from the water by paddle boaters and taken to nearby Fort Williams by a Sea Tow vessel, a Coast Guard spokesman said the next day. By the time Hanson reached rescuers on shore, he was unresponsive. He never regained consciousness.

On May 9, the National Transportation Safety Board released its final determination report.

It stated that the plane crash was caused by “a fatigue failure of the No. 3 piston skirt, which resulted in a total loss of engine power and the subsequent ditching in the ocean.”

Although the No. 3 piston was overhauled about five years before the accident, it was an original piston on the engine, which was more than 65 years old, the report states.

“Post-accident examination of the airplane’s engine revealed that the No. 3 piston skirt fractured, and the resultant debris entered the engine and camshaft gear, affecting the magneto timing,” the report states.

Metallurgical examination of the piston skirt at the NTSB Materials Laboratory in Washington, D.C., revealed fatigue originating near a machined through-hole.

The examination revealed two fracture surfaces on the piston skirt, which was smeared with mechanical contact, the report states.

Manufactured in 1946, Hanson’s plane was equipped with a 150-horsepower engine that was installed new in 1947, according to the report.

“During a telephone interview, the mechanic who overhauled the pistons in 2007 stated that he was not surprised that one failed, as they were 60 to 70 years old,” the report states.

The mechanic said that as part of the overhaul procedure, he balanced the six pistons by ensuring they were the same weight.

Last month, Eric Weiss, an NTSB spokesman in Washington, D.C., said the piston skirt is the portion of the piston that extends the lowest.

It keeps the piston from rocking excessively in the cylinder.

Weiss said the piston skirt is typically machined with small grooves to help hold and transport oil to the cylinder walls to provide proper lubrication.

In a combustion engine, the pistons are sealed inside the cylinder walls by the piston rings, Weiss said. The rings are making contact with the cylinder wall while the piston rides up and down, centered by the rings in the cylinder wall.

As the piston is changing direction at the top and bottom of each stroke, the piston rocks, Weiss said. It is then that the piston skirt makes contact with the cylinder wall, setting the piston straight once again to continue its path, he said.

Hanson’s path on June 24 started at about 10:30 a.m. when he flew the plane from Twitchell’s Airport in Turner.

According to the FAA, the Voyager was in radio and radar contact with Portland International Jetport in Portland as Hanson flew it along the coast between 500 and 1,000 feet above the ocean from south to north.

He radioed that he was flying low for sightseeing and photography. At 11:54 a.m., Hanson radioed that the airplane had experienced a total loss of engine power at about 500 feet up, according to the report.

Hanson “indicated that he was not going to be able to glide the airplane far enough to reach the shore,” the report states.

The last radar target was recorded at 11:55 a.m., indicating an altitude of 200 feet above the ocean.

Two days after the crash, a Maine medical examiner’s autopsy revealed Hanson died of “blunt force injuries of neck and chest with hypothermia and submersion.”

Standard toxicology testing in such incidents showed that Hanson had Dextromethorphan, or cough suppressant, in his liver and blood, according to the report.


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