The RV-8 pilot reported that, during cruise flight, he felt a sustained vibration, which he thought was from the engine or propeller, and that the airplane then started to slow down.
He made a forced landing to the desert near Wickenburg, Ariz., and the plane came to rest on its nose, which caused substantial damage.
A post-accident propeller examination revealed that one of the propeller pitch change pins had broken. The pin’s fracture would have resulted in the sustained vibration and loss of speed reported by the pilot.
A metallurgical examination of the pin revealed that it had failed due to a fatigue crack that had progressed through about 70% of the pin. The fatigue crack initiated at dimples that had a depth and width consistent with excessive shot peening, which likely occurred during the manufacturing process.
The NTSB determined the probable cause as the fatigue failure of a propeller pitch change pin due to excessive shot peening of the pin’s surface during the manufacturing process.
NTSB Identification: WPR14LA046
This November 2013 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
The docket contains several items that are very interesting. According to one document, after the emergency laning the very tech saavy pilot spoke with the Hartzell tech rep. The pilot reported that the tech rep strongly assertd the problem with the prop in fracture was the off airport landing and prop strike. It wasn’t until the pilot/builder trotted out his “normal” and “mayday flight”engine monitor data that the Hartzell tech rep and FSDO acknowledged the real cause of the accident was a part that suffered from a manufacturing defect. This was confirmed in the metalurgy report (included in the docket). If there’s a lesson in this accident it’s that the ‘facts’ i.e. DATA are incredibly important. (Forgive this diversion… But the lesson is too powerful to inore…) Too bad this same respect for physical evidence doesn’t carry over to some of our current social controversies.