Incident Overview
On September 6, 2020, at approximately 0900 eastern daylight time, a Robinson R22 Mariner helicopter, registration N194HC, was involved in an accident near Fort Myers, Florida. The helicopter was being operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The commercial pilot and the airline transport-rated pilot receiving instruction were not injured.
Pilot Statements and Observations
Both pilots submitted consistent written statements. Preflight and engine-start procedures were completed without anomalies. As the engine accelerated to near its operating rpm, both pilots heard a loud "bang." The pilot receiving instruction leaned out his door and announced that "the tail was hanging off the back of the aircraft." The pilots then shut down the helicopter and reported the event to the owner and mechanic.
In a subsequent telephone interview, the pilot receiving instruction stated that after shutdown, he observed no evidence that an unsecured aircraft cover, clothing item, or bird had struck the tailrotor. He added that the only debris on the ramp was aircraft wreckage.
Examination of Wreckage
Photographs of the helicopter revealed damage to the tailrotor driveshaft, tailrotor gearbox, tailrotor blades, and the section of the tailcone forward of the tailrotor gearbox. These components were sectioned and sent to the NTSB Materials Laboratory in Washington, DC, for further examination.
Materials Laboratory Findings
Examination of all submitted components showed signatures consistent with overstress fracture on all fracture surfaces. There was no evidence of fatigue. Additionally, there was no mechanical, paint transfer, or biological evidence of foreign object damage (FOD). The fractures and impact signatures were consistent with the fracture of the tailrotor gearbox mount structure (bulkhead) of the tailcone, followed by impact signatures of the rotating tailrotor assembly against the vertical and horizontal stabilizers.