Bell Helicopter Textron Canada 407 N31PB accident near North Charleston, South Carolina

Probable cause

A failure of the tail rotor pitch change lever assembly due to incorrectly installed bolts and maintenance personnel’s inadequate inspection of the tail rotor control system.

NTSB analysis

The pilot reported that, about 35 minutes into the flight, he noticed that the helicopter began to yaw to the right and his pedal inputs did not correct the situation. He contacted the tower at his destination and declared an emergency. As he approached the runway for a straight-in landing, the helicopter yawed again. He lowered the collective, but the helicopter continued to yaw right. He then reduced the throttle and attempted to maintain a level attitude. The helicopter struck the ground at a high rate of descent, coming to rest in the grass adjacent to runway. The helicopter sustained substantial damage to the fuselage, main rotor system, and tail rotor system.

A postaccident examination of the helicotper found one of the two bolts that secured the tail rotor pitch change lever assembly was missing. The lever assembly was disconnected from the trunnion, resulting in the loss of tail rotor control. The other bolt that connected the levers to the rod assembly was in place, but loose; the cotter pin for its attachment nut was missing.

A review of the maintenance records revealed that a 300 hour/3 month inspection was performed on the helicopter about 15.4 flight hours before the accident. According to the helicopter manufacturer, that recent inspection would not have required removal of the lever assembly bolts; however, the nuts and bolts should have been clearly visible during the inspection of the area. The mechanic who performed the inspection stated that he must have overlooked them.

Text from the NTSB. Open the NTSB docket for ERA23LA319 for the full record.