Bell 206 crash near Marathon, TX, United States

HISTORY OF FLIGHTOn August 8, 2020, about 1100 central daylight time, a Bell 206B helicopter, N284S, was destroyed when it was involved in an accident near Marathon, Texas. The pilot was seriously injured, and the three passengers were fatally injured. The flight was operated as a Title 14 Code of Federal Regulations Part 91 aerial survey flight. The flight was conducting an aerial survey in the Texas Black Gap Wildlife Management Area. The pilot reported that, about 5 minutes before the helicopter was to be refueled, he felt a “slight” vibration; at that time, the helicopter was operating at an altitude of about 800 ft above ground level and an airspeed of about 69 knots. The pilot further reported that the vibration, which lasted less than 30 seconds, started as a “slight vertical vibration” but “immediately intensified to a severe lateral vibration” that made the helicopter “impossible to control.” The pilot stated that the vibration affected the main rotor system blades and that he felt most of the vibration through the collective and airframe with no vibration in the anti-torque pedals. The pilot informed the passengers that he would be conducting an emergency landing. The pilot recalled that during the emergency landing, he observed two distinct blade paths prior to impact. The helicopter lost lift and subsequently impacted 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 INFORMATIONThe pilot reported that he had accumulated about 2,500 flight hours in Bell 206L and 206B helicopters conducting aerial surveys in Texas, Alaska, Utah, and New Mexico. AIRCRAFT INFORMATIONAccording to the helicopter’s maintenance records, in November 2019 at Van Horn Aviation, Tempe, Arizona, for main rotor blade A092, the tip abrasion strip and trim tab were removed and replaced due to a trim tab debonding. For main rotor blade A093, the trim tab was removed and replaced for inspection. Both blades had a component total time of 829 hours. Main rotor blades serial Nos. A092 and A093 were installed on the accident helicopter on March 1, 2020, at a total helicopter time of 14,917 hours, and both blades had a component total time of 928 hours. Three 100-hour/12-month inspections were performed after installation, including an inspection performed on August 2, 2020 (6 days before the accident). On July 1, 2020, the engine was removed and replaced due to reports of a high turbine outlet temperature and low power. According to the helicopter’s flight manual and the helicopter’s most recent weight and balance records, the helicopter’s maximum gross weight was 3,200 pounds, and the empty weight was 1,908 pounds. The operator estimated that the helicopter’s weight at the time of the accident was 2,700 pounds. The helicopter was not equipped with, and was not required to be equipped with, a crash-resistant flight recorder or cockpit image recorder. METEOROLOGICAL INFORMATIONThe pilot reported the temperature about the time of the accident was “heating up pretty good pushing around 100 degrees [Fahrenheit]” and did not recall the density altitude. AIRPORT INFORMATIONAccording to the helicopter’s maintenance records, in November 2019 at Van Horn Aviation, Tempe, Arizona, for main rotor blade A092, the tip abrasion strip and trim tab were removed and replaced due to a trim tab debonding. For main rotor blade A093, the trim tab was removed and replaced for inspection. Both blades had a component total time of 829 hours. Main rotor blades serial Nos. A092 and A093 were installed on the accident helicopter on March 1, 2020, at a total helicopter time of 14,917 hours, and both blades had a component total time of 928 hours. Three 100-hour/12-month inspections were performed after installation, including an inspection performed on August 2, 2020 (6 days before the accident). On July 1, 2020, the engine was removed and replaced due to reports of a high turbine outlet temperature and low power. According to the helicopter’s flight manual and the helicopter’s most recent weight and balance records, the helicopter’s maximum gross weight was 3,200 pounds, and the empty weight was 1,908 pounds. The operator estimated that the helicopter’s weight at the time of the accident was 2,700 pounds. The helicopter was not equipped with, and was not required to be equipped with, a crash-resistant flight recorder or cockpit image recorder. WRECKAGE AND IMPACT INFORMATIONThe helicopter impacted hilly, rocky terrain in a remote area of west Texas at an elevation of about 5,160 ft. An on-scene examination revealed that most of the wreckage was in a compact area with the farthest piece of wreckage, a tip end section of a main rotor blade, estimated to be about 80 ft from the main wreckage. The postimpact fire consumed most of the main wreckage (the fuselage, engine, transmission, and portions of the main rotor blades). The tailboom had separated and was located near the fuselage; and the tailboom had sustained limited thermal damage. Further examination of the tailboom showed that it was fractured in two large segments: the forward section containing the horizontal stabilizer and the aft section containing the vertical stabilizer and tail rotor. The aft end of the forward tailboom section was deformed to the right and showed evidence consistent with contact by a main rotor blade. The forward landing gear cross-tube exhibited significant deformation; the aft crosstube showed minor deformation. The left and right skid tubes were fractured in multiple locations. The main rotor assembly, including the yoke, mast, and swashplate, exhibited thermal damage, and no anomalies that would have precluded normal operation were noted with the assembly. Both main rotor blades’ inboard section remained attached to the yoke, displayed fractures located about 48 inches outboard of the yoke, and exhibited thermal damage. Large midspan-to-outboard end segments were found near the tail rotor and vertical stabilizer. A 20-inch section of one main rotor blade tip (referred to as blade A) was found about 80 ft from the main wreckage. Smaller sections of blade skin and foam core were distributed within the main wreckage area. The main transmission housing was partially consumed by the postcrash fire. The engine-to-transmission driveshaft remained attached to the main transmission input quill and remnants of the freewheeling unit. Rotational scoring was noted on the driveshaft. The tail rotor remained installed on the tail rotor gearbox output shaft, and both tail rotor blades remained installed on the tail rotor yoke. Both tail rotor blade tips displayed impact damage, and the remainder of the blades were relatively intact. No anomalies that could have precluded normal operation were noted with the tail rotor system. The tail rotor drive train exhibited fragmentation. All drive shaft segments were located, and rotational scoring was noted at the hanger bearing locations within the tailboom sections. Continuity through the tail rotor gearbox was noted when the gearbox was manually rotated. No evidence indicated any binding or abnormal sounds. Flight control continuity could not be established due to thermal and impact damage. Various pieces of connection hardware and bellcranks for the flight control system did not exhibit evidence of separation at their respective fasteners. The engine was located within the main wreckage on its left side at its normally installed location. The engine did not exhibit signatures of uncontainment or separation between its modules. Disassembly of the engine revealed no anomalies that would have precluded normal operation. The engine fuel system and components were unable to be tested due to thermal and impact damage. The cockpit instruments, including the caution and warning panel, exhibited significant damage due to impact and thermal damage. Materials Laboratory Examination