History of Flight
On August 8, 2020, about 1100 central daylight time, a Bell 206B helicopter, registration N284S, was destroyed when it impacted terrain near Marathon, Texas. The pilot was seriously injured, and the three passengers were fatally injured. The flight was a Title 14 Code of Federal Regulations Part 91 aerial survey flight in the Texas Black Gap Wildlife Management Area.
The pilot reported that, about 5 minutes before a planned refueling, he felt a slight vertical vibration lasting less than 30 seconds. The vibration immediately intensified to a severe lateral vibration, making the helicopter impossible to control. The pilot felt the vibration through the collective and airframe, with no vibration in the anti-torque pedals. He informed the passengers of an emergency landing and observed two distinct blade paths prior to impact. The helicopter lost lift and struck terrain short of the intended landing area. A postimpact fire ensued. The pilot stated that the engine was producing power at the time of the accident.
Personnel Information
The pilot reported approximately 2,500 flight hours in Bell 206L and 206B helicopters conducting aerial surveys in Texas, Alaska, Utah, and New Mexico.
Aircraft Information
The helicopter was a Bell 206B with maximum gross weight of 3,200 pounds and empty weight of 1,908 pounds. The operator estimated the accident weight at 2,700 pounds.
Main rotor blades serial numbers A092 and A093 were installed on March 1, 2020, at a total helicopter time of 14,917 hours and component total time of 928 hours. In November 2019, at Van Horn Aviation in Tempe, Arizona, the tip abrasion strip and trim tab on blade A092 were removed and replaced due to a trim tab debonding; the trim tab on blade A093 was removed and replaced for inspection. Three 100-hour/12-month inspections were performed after installation, including one on August 2, 2020. On July 1, 2020, the engine was removed and replaced due to reports of high turbine outlet temperature and low power.
The helicopter was not equipped with a crash-resistant flight recorder or cockpit image recorder.
Meteorological Information
The pilot reported the temperature at the time was “heating up pretty good pushing around 100 degrees [Fahrenheit]” and did not recall the density altitude.
Wreckage and Impact Information
The helicopter impacted hilly, rocky terrain at an elevation of about 5,160 ft. Most wreckage was in a compact area; the farthest piece, a main rotor blade tip section, was about 80 ft from the main wreckage. The postimpact fire consumed most of the fuselage, engine, transmission, and portions of the main rotor blades. The tailboom separated and was fractured into two segments, with the forward section deformed to the right, consistent with contact by a main rotor blade. The landing gear exhibited deformation and fractures. The main rotor assembly showed thermal damage but no pre-impact anomalies. Both main rotor blades had fractures about 48 inches outboard of the yoke and midspan-to-outboard segments near the tail rotor. The tail rotor system was intact with impact damage. The tail rotor drive train was fragmented. Flight control continuity could not be established due to damage. The engine showed no uncontainment or separation, and disassembly revealed no anomalies preventing normal operation. Cockpit instruments were significantly damaged.
Materials Laboratory Examination
Portions of the main rotor blades were examined. Six pieces of blade A were recovered; the largest fragment was about 9 ft long. The lower skin showed translaminar fractures with slanted surfaces, consistent with bending. Impacts were noted on the leading-edge abrasion strip at two locations. X-ray fluorescence showed material transfer. Fracture surface analysis of the tapered tip section revealed curved crack arrest marks over about 0.4 inches, consistent with progressive fracture under dynamic loading. Striations consistent with fatigue were observed over about 58% of the fracture surface. Blade B was about 11 ft long with thermal damage. Fractures in the abrasion strip and trailing edge were consistent with aft bending. Tip fragments showed no thermal damage, indicating fragmentation before the fire.