Garlick Helicopters Inc OH-58A+ N48LA accident near Newport, Tennessee

Probable cause

Inadequate maintenance inspections of the main rotor blade inertia screw holes, which resulted in a main rotor blade failure due to fatigue. Contributing to the accident was the pilot's inadequate preflight inspection of the main rotor blades.

NTSB analysis

The pilot completed a preflight inspection and found no problems with the helicopter. He then completed a normal start procedure and increased the rpm to 100 percent flight idle. He was about to increase the collective, when he felt a violent shake, heard a loud noise, and the helicopter began to come apart. A postaccident examination of the wreckage revealed that an outboard 2-foot section of main rotor blade had separated. Metallurgical examination of the separated blade revealed that a fatigue crack originated from an inertia screw hole, located at the bottom surface of the spar portion of the main rotor blade. That crack propagated more than 50 percent of the spar cross section, before fracturing consistent with overstress. A manufacturer alert bulletin instructed operators to visually inspect the inertia screw hole locations on the blade spar with a 10X magnifying glass for cracks and corrosion every 8 hours of flight, or 32 cumulative flights. The outboard section of main rotor blade was secured with eight inertia screws. Although the inertia screw holes were supposed to receive a maintenance inspection every 8 flight hours, they were also a preflight inspection item for the pilot. Review of the helicopter's maintenance logbooks revealed an entry stating that the inertia screw holes had been inspected within the past 8 flight hours; however, corrosion was present in the inertia screw hole that failed. The corrosion and fatigue was most likely present for more than 8 flight hours.

Text from the NTSB. Open the NTSB docket for ERA10LA379 for the full record.