BELL UH 1B near Detroit, OR — 2013-09-16

Probable cause

The fatigue failure of the upper two tailboom attachment points, which resulted in the tailboom separating from the fuselage during logging operations. Contributing to the accident was poor maintenance throughout the helicopter’s operational life.

Contributing factors

Contributing to the accident was poor maintenance throughout the helicopter's operational life.

NTSB narrative

Witnesses reported that, when the helicopter was just above the trees during an external load logging operation, they either observed or heard the load of logs release early and impact the ground hard. Witnesses then observed the helicopter's tailboom separate from the fuselage and descend through the trees. The fuselage impacted the ground inverted, and the tailboom came to rest about 140 ft away. A mechanic reported that the pilot had indicated before the flight that the helicopter felt like it "shuffled" during translational lift; however, the mechanic suspected that the transmission mounts were starting to wear and would need to be changed at a later date. Postaccident examination of the airframe and engine revealed control continuity throughout the airframe except for a portion of the tail rotor drive shaft that extended from the transmission, which was not found. The tailboom had separated from the aft fuselage at the tailboom attachment points. The lower two tailboom attachment fittings exhibited features consistent with overstress failure and did not show indications of fatigue and/or other failure modes. The upper two tailboom attachment fittings both contained fatigue cracks throughout almost the entire fracture surface. The pilot purchased the helicopter about 3 years before the accident; that same year, the helicopter was issued a new airworthiness certificate. According to the Federal Aviation Administration, the previous owner had relinquished the helicopter's airworthiness certificate to avoid punitive action for poor maintenance of the helicopter. Maintenance records located within the helicopter did not contain sufficient information to determine when the most recent maintenance was performed; however, the documents did reveal that several component inspections were not completed within the manufacturer's recommended time. It is likely that long-term, inadequate maintenance of the helicopter contributed to the failure and separation of the tailboom.

Analysis

Primary failure mode

Mechanical failure

First missed decision gate

Pilot could have addressed maintenance issues before flight.

NTSB coding

• Part(s) separation from AC · Maneuvering-low-alt flying

Evidence available

• 10 docket documents

Docket documents10

• Evidence Control Form - Tail Boom Attachment Pointsform
• Release of Aircraft Wreckage, NTSB Form 6120.15form
• Release of Aircraft Wreckage, NTSB Form 6120.15form
• Statement of Party Representatives to NTSB Investigationinterview
• Witness Interviewsinterview
• Record of Conversation - FAAother
• Airframe and Engine Examination Reportreport
• Materials Laboratory Factual Reportreport
• Toxicological Reportreport
• On Scene Wreckage Diagram (Courtesy of FAA)wreckage

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