During a checkout flight for a newly licensed pilot June 12, the flight instructor noticed something wrong, the Bangor Daily News reported.
"We got to around 1,500 feet and we heard a loud bang and the plane started shaking," said Rick Eason, faculty adviser for the University Flying Club in Orono.
The plane made an emergency landing at Bangor International Airport, where Eason said he was contacted by the airport's control tower and "asked if I lost something from my plane."
It turned out a piston wrist pin, a part 4 inches long that connects the arm and head of a piston inside a plane engine's cylinder, broke off the Cessna 172 and hit a Bangor man's home.
The small piece did an estimated $5,000 in damage to the home after it fell through the attic and sheetrock ceiling of the house and came to rest on the hardwood floor of the foyer.
"We've never had anything like this. We haven't had any in-flight problems like this," the flight instructor said.
Eason reported the incident to the Flight Standards District Office in Portland, a regional division of the Federal Aviation Administration.
"We don't know why it happened," said Soren Hansen, the flying club's mechanical officer.
FAA spokesman Jim Peters said a federal inspector has confirmed the incident and the investigation is waiting for Easton to send a report after the aircraft is repaired, as well as the Bangor homeowner to record the details of the accident.
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