Bell 206L-3 N210MH accident near Kearny, New Jersey

Probable cause

The deliberate concealment and reuse of an unairworthy tail rotor driveshaft by unknown personnel, which resulted in an overstress separation at a bonded flange adapter as a result of driveshaft imbalance.

NTSB analysis

The pilot reported that, during a 20-ft hover, the helicopter spun right. The pilot made left pedal inputs; however, the helicopter then rotated three times to the right. The pilot decreased the throttle and increased the collective before the helicopter landed hard.

Postaccident examination of the helicopter revealed that the No. 5 tail rotor driveshaft tube had separated from its bonded flange adapter, where it had been secured by adhesive. The driveshaft tube had been freshly painted. When some of the paint was removed, hand written markings in red ink reading "X," ".004," and ".024" were noted on the tube. The numbers were on either end of the tube and were likely measured runout values for the shaft, and, because they exceeded the maximum runout requirement of .003 inch, the "X" mark was made to indicate that the tail rotor shaft was unairworthy. However, at some point after the red markings were made, the unairworthy shaft was repainted by unknown personnel, which obscured the markings. It is likely that the driveshaft became imbalanced because it was beyond its runout tolerance, which led to the overstress separation of the tube from the bonded flange adapter.

A representative of the current owner reported that the owner had recently purchased the helicopter. About 5 years before the purchase, the helicopter had experienced a hard landing, and it had not been flown during the subsequent 5 years. The current owner received the helicopter with the driveshaft freshly painted. When he inquired about the fresh paint, the previous owner told him that the driveshaft was purchased at auction. The current owner did not receive serviceable tags with the driveshaft but did receive an auction invoice; however, no serial numbers were listed on the invoice. The serial number format found etched on the driveshaft did not match any known records. Therefore, the investigation could not determine if the separated driveshaft was the same driveshaft that was installed on the helicopter when it experienced the hard landing. As a result of the accident examination, the helicopter manufacturer submitted a suspected unapproved parts report to the Federal Aviation Administration.

Text from the NTSB. Open the NTSB docket for ERA15LA218 for the full record.