Diamond DA 40 N386MA accident near Benson, Arizona

Probable cause

The failure of the nose landing due to fatigue cracking.

NTSB analysis

The pilots were performing an instructional flight and completed a normal approach to the destination runway. The main landing gear touched down on the runway surface first and as soon as the nose lowered, the nose landing gear collapsed.

The nose landing gear fork assembly had collapsed when a pivot-axle welded to the arm in the nose landing gear welding assembly fractured. A metallurgical examination revealed the pivot-axle fracture surface exhibited two opposite facing fatigue cracks propagating inward on the pivot-axle due to reverse bending, consistent with repeated landing forces and cycles prior to the accident. The cracks propagated until the remaining pivot-axle cross section could not withstand the loads on the last landing cycle and succumbed to fracture from overstress.

The location of the crack’s origins required disassembly to detect. Therefore, it would not have been easily detected during routine maintenance. Following this accident, the manufacturer issued a mandatory service bulletin to routinely inspect the nose landing gear for cracks using dye penetrant.

Text from the NTSB. Open the NTSB docket for WPR20LA290 for the full record.