Robinson Helicopter R22 BETA N26NE accident near Ellington, Connecticut

Probable cause

The separation of the collective push-pull tube and jackshaft assembly, which resulted in the total loss of helicopter control and collision with terrain. Contributing to the accident was the inadequate supervision of maintenance personnel by the operator during overhaul, which resulted in inadequate tightening force applied to the collective jackshaft attachment hardware, and the failure of maintenance personnel to detect the loose hardware during subsequent inspections.

NTSB analysis

According to the flight instructor, the helicopter remained at traffic pattern altitude in order to conduct a practice autorotation. As the helicopter turned onto the final leg of the traffic pattern, the instructor and the pilot receiving instruction initiated an autorotation from about 950 feet above ground level by lowering the collective and reducing the throttle. Upon entry, the pilots observed an "excessively high" rotor rpm indication that continued to climb toward the top of the tachometer. Both pilots raised the collective control and pushed the cyclic control forward to decrease the rotor rpm, but the rotor rpm remained high and did not respond to control inputs. As the helicopter approached the runway, the instructor elected to terminate the autorotation with power and instructed the pilot to "join" the needles on the dual tachometer by restoring full engine power. Both the instructor and the pilot applied engine power simultaneously; however, the engine tachometer indicated an overspeed condition. The instructor assumed sole control of the helicopter and initiated a deceleration, but the helicopter pitched up, rolled right, and impacted the ground on its side, resulting in substantial damage to the main rotor and fuselage.

Examination of the wreckage revealed that the vertical collective control push-pull tube was disconnected from the collective jackshaft assembly. A search of the wreckage resulted in the recovery of the attachment bolt and its associated washers and locknut, but the locking device was not found. Examination of the bolt and locknut threads revealed that they were undamaged. The bolt, locknut, washers, spacers, and the interior bore of the collective jackshaft assembly exhibited radial and axial smearing and fretting wear scarring of their contact surfaces. The wear was consistent with a lack of tightening force on the attachment hardware at installation. The helicopter's most recent overhaul was completed about 2 years before the accident, and subsequent inspections were performed between the time of the overhaul and the accident. The operator stated that he, along with licensed and unlicensed mechanics who he supervised, worked on the helicopter during the 6 months required for completion of the overhaul.

Text from the NTSB. Open the NTSB docket for ERA13LA116 for the full record.