Accident Overview
On November 1, 2016, at about 1130 eastern daylight time, a Bell OH-58C helicopter, registration N139RD, operated by Helicopter Applicators Inc., was substantially damaged following a main rotor blade fracture during initial climb after takeoff in Cameron, North Carolina. The commercial pilot sustained minor injuries. Visual meteorological conditions prevailed, and no flight plan was filed for the local aerial application flight under 14 CFR Part 137.
Pilot Account
The pilot reported that he had flown earlier in the day at a different field, spraying an herbicide, making approximately 12 landings on a truck to refill. He then flew to a new field, sprayed one load, landed, and waited for the loading crew. After loading 80 gallons (720 pounds) of herbicide, he took off and climbed to about 50 ft. After traveling about 200 yards from the staging area, he heard a loud bang, and the helicopter fell to the ground.
Witness Observations
A witness stated that shortly after takeoff, the tailboom appeared to move to the left, then straight up and into the main rotor blades. The helicopter then fell straight down, and the witness assisted the pilot out.
Wreckage Examination
An FAA inspector found the helicopter resting on its left side. Damage to the tailboom was consistent with main rotor blade strikes about 10 ft from the fuselage. One main rotor blade's outboard portion was found about 1,000 ft away.
NTSB examination revealed that the "white" main rotor blade (part No. 206-011-250-3, serial No. TLK-9054) had two fractures: inboard near the root (overload) and outboard about 28 inches from the tip (fatigue features with curving arrest lines). The "red" blade was generally intact. The transmission separated and the main rotor mast bent, with transmission separation consistent with pre-impact condition.
Metallurgical Findings
The fractured outboard portions were sent to the NTSB Materials Laboratory. Fatigue features originated from multiple origins near the inertia weight attachment hole. The fatigue region measured 1.4 inches from the leading edge and 3 inches from the trailing edge of the hole.
Service Bulletins
Bell Helicopter Textron published Military Alert Bulletin (MAB) USA-OH-58-87-1, revision B (originally August 12, 1987, revised April 12, 2007), requiring visual inspections (10x scope) of main rotor blades (part numbers 206-011-250-003/113) for inertia weight screw heads. Paint removal and clear-coat finish were required for initial and subsequent inspections at intervals of 8 hours or 32 flights. Bell also issued Operations Safety Notice (OSN) OSN-GEN-07-38, Revision A, on April 12, 2007, referencing the MAB. Both noted the inspection did not apply to blades with serial numbers A-1 and subsequent.
Inspection Compliance
NTSB examination found black paint on the lower leading edge of the blade with erosion wear, and no evidence of clear-coat finish on the inertia weight attachment hole as required by MAB and OSN.
Aircraft History and Maintenance
The accident helicopter (serial No. 71-20396) was manufactured in 1971, originally U.S. Army, and received FAA special airworthiness certificate for agriculture on May 4, 1999. The most recent 100-hour inspection was completed on September 29, 2016, with total airframe time 12,604.5 hours and engine time 2,690.3 hours. The operator was unaware of the MAB and initiated a campaign to inspect their OH-58 fleet.
Applicable Inspection Programs
Garlick Helicopters' preventive maintenance inspection program (GHI-OH58-PMS) included daily inspections for nicks, scratches, etc., and 25-hour inspections for protective coating, but no specific inspection of the inertia weight area. Rotorcraft Development Corporation stated they did not have the MAB and OSN.