Bell OH 58A N916PD accident near Sacramento, California

Probable cause

The failure of the vertical stabilizer due to fatigue.

NTSB analysis

The pilot reported that during the takeoff, flight, and landing for a local routine helicopter patrol flight, he did not experience any turbulence nor did any of the flight controls reveal an indication that something was wrong. The pilot reported that during the postflight inspection, the vertical stabilizer was found bent downward away from the tail rotor.

A postaccident examination of the vertical stabilizer revealed a fatigue crack that initiated at the aft end of the inboard skin at about the middle of the span. A stop-drill hole was present above the upper aft attachment hole, indicating that the vertical stabilizer was allowed to continue in service after a crack had been detected that extended about 1 1/4 inches from the aft edge of the inboard edge. The crack intersected the lower side of the stop-drill hole, and a fatigue crack reinitiated from the forward side of the stop-drill and continued to propagate towards the leading edge.

The operator acquired the helicopter as US Army surplus. Since 2003, the US Army’s daily inspection checklist included inspection for cracks originating from the four attachment inserts on the inboard of the vertical stabilizer. The operator’s maintenance vendor was not aware of the US Army aviation safety action message for the daily inspection for cracks inboard of the vertical stabilizer. Had those daily inspections of the vertical fin attachment area been accomplished, these cracks would likely have been identified.

Text from the NTSB. Open the NTSB docket for WPR17LA034 for the full record.