By Alexandra Skores, CNN

Washington (CNN) — “Excessive grinding” during maintenance led to a metal pin cracking and eventually breaking causing the left landing gear to collapse on an Alaska Airlines flight in 2023, the National Transportation Safety Board said in a final report Tuesday.

On August 20, 2023, the Alaska Airlines Boeing 737-800 was landing at John Wayne-Orange County Airport in California when the gear failed, sending sparks flying as the engine scraped the runway.

There were 112 passengers and crew on board, who had to evacuate from stairs onto a taxiway, but no injuries were reported.

When the plane touched down, the captain reported feeling a “firm jolt” and the plane was “pulling reasonably hard” to the left.

In the NTSB’s analysis, a “fatigue crack,” in a metal pin 0.144 inches deep, was “large enough to cause the remaining material of the 10-inch-long pin to fracture… during landing, resulting in the collapse of the left main landing gear.”

The “excessive grinding” of the surface of the pin likely happened during a maintenance overhaul on July 5, 2018, after it was covered in chrome, the NTSB said.

The grinding caused too much heat, which made the metal softer and more likely to break.

The crack wasn’t present at the time of the maintenance work but likely developed after about 4,000 subsequent landings, the board found.

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