On September 17, 1995, a Piper PA-12 (registration N3334M) was involved in an aviation accident near Aniak, AK. Investigators recorded the probable cause as: The pilot's failure to see and avoid a soft gravel berm on the runway, which resulted in main landing gear failure and a subsequent nose-down attitude. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
The pilot landed on a 6,000-foot gravel runway and failed to see a soft berm. The left main wheel separated upon impact, causing the airplane to nose down.
What happened
The pilot reported that he was conducting a landing operation on a 6,000-foot-long gravel runway. During the approach and touchdown phase, the aircraft encountered an obstruction that was not visible until it was too late to avoid. The pilot stated that he did not see a soft, gravel berm located on the runway surface prior to making contact with the ground.
Upon landing, the accident airplane's main landing gear struck the berm. This impact caused immediate structural failure of the left side of the undercarriage. Specifically, the left main wheel separated from the landing gear at the axle. The sudden loss of support on the left side resulted in the aircraft collapsing forward onto its nose.
The investigation
The narrative provided by the pilot indicates that the primary mechanical failure was a direct result of the impact with the unmarked or poorly visible gravel berm. The separation of the wheel from the axle suggests that the force of the impact exceeded the structural limits of the landing gear attachment point.
Probable cause
The pilot's failure to see and avoid a soft gravel berm on the runway, which resulted in main landing gear failure and a subsequent nose-down attitude.