NTSB Factual Report

On July 28, 2010, about 0900 eastern daylight time, an experimental Garlick Helicopters OH-58A+, N48LA, operated by B & S Air Inc., was substantially damaged while standing in a field, with the engine operating, near Newport, Tennessee. The certificated commercial pilot incurred minor injuries. The aerial application flight was conducted under the provisions of 14 Code of Federal Regulations Part 137. Visual meteorological conditions prevailed and no flight plan was filed for the planned flight to Jackson, Tennessee.

According to the pilot's written statement, he performed a normal preflight inspection and found no problems with the helicopter. He then completed a normal start procedure and increased rpm to 100 percent flight idle. The pilot was about to increase collective, when he felt a violent shake, heard a loud noise, and the helicopter began to come apart. He then saw the transmission and rotor blades on the ground in front of helicopter. He subsequently shut off the engine and exited the helicopter.

Examination of the wreckage by a Federal Aviation Administration (FAA) inspector revealed that an outboard 2-foot section of main rotor blade had separated. The transmission had also separated, which resulted in substantial damage to the fuselage. The separated section of main rotor blade was forwarded to the NTSB Materials Laboratory, Washington, DC, for further examination.

Metallurgical examination 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.

The helicopter was manufactured in 1970 and delivered to the U.S. Army. In 1995, it was transferred from the U.S. Army to state law enforcement. The helicopter was subsequently equipped for agricultural application and issued an FAA experimental airworthiness certificate in 2005. According to maintenance records and the pilot, the helicopter's most recent 100-hour inspection was completed on June 15, 2010. At that time, the helicopter had accumulated approximately 6,704 total hours of operation. The helicopter had accumulated about 76 additional hours of operation, from the time of the last 100-hour inspection, until the accident.

According to a representative from the helicopter manufacturer, Bell Military Alert Bulletin USA-OH-58-87-1 was issued on June 12, 1987, requesting military operators to visually inspect the inertia screw hole locations on the blade spar with a 10X magnifying glass for cracks and corrosion. The inspection should be done at every 8 hours of flight, or 32 cumulative flights. Subsequently, on April 12, 2007, Bell Operations Safety Notice OSN-GEN-07-38 was issued to all OH-58 operators and referenced the Bell Military Alert Bulletin.

According to the FAA inspector, 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 with no anomalies noted; however, the inspector observed corrosion present in the inertia screw hole that failed.

NTSB 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.