Bell UH 1H N111DR accident near Olympia, Washington

Probable cause

A loss of tail rotor thrust due to the improper installation of the tail rotor assembly by maintenance personnel resulted in the pilot’s inability to maintain control of the helicopter as he began transition into forward flight from a hover, which resulted in a hard landing. Contributing to the accident was the failure of company quality control personnel to identify the improper installation of the tail rotor assembly before certifying the helicopter for flight, and the pilot’s inadequate preflight inspection.

NTSB analysis

The purpose of the maintenance test flight was for a track and balance of the tail rotor and main rotor blades. The pilot reported that during his preflight check and walkaround, everything looked fine with no anomalies noted. After becoming airborne and performing a hover check, the pilot proceeded to transition to forward flight, when he experienced a loss of tail rotor thrust. This led to a near-vertical rotating descent and hard landing, which resulted in substantial damage to the tailboom and lower fuselage.

On on-site examination found that both pitch change link bolts and the tail rotor pitch change horn were only finger tight and found no evidence of cotter pin installation. One of the two crosshead bolts found in the debris field showed thread wear damage but was observed to be relatively complete.

The accident could have been prevented if, during the rigging process of the tail rotor assembly, the crosshead bolts and the tail rotor pitch change bolts had been properly torqued and cotter pins had been installed. Additionally, had company quality control personnel identified the improper installation of the tail rotor assembly before certifying the helicopter for flight, or had the pilot detected the missing cotter pins during his preflight inspection, the anomalies could have been corrected.

Text from the NTSB. Open the NTSB docket for WPR18LA147 for the full record.