Zephyrhills, FL, USA
N777CP
BELL 206
While in cruise flight, the pilot heard a binding sound and felt a reduction in engine power. The low rotor rpm aural alarm then sounded, and he initiated an autorotation to swampy terrain. The helicopter came to rest amongst pine trees and undergrowth. The tailboom was impact separated and the main rotors were fractured about midspan. During a detailed examination of the helicopter, the “B” nut at the engine fuel control unit was found loose with no thread engagement. During a test run of the engine, the “B” nut was tightened and torqued to proper specification. The engine ran smoothly and continuously at all power settings. A review of the helicopter’s maintenance records revealed the last annual inspection was completed about 75 hours prior to the accident. The pilot, who also holds an airframe and powerplant certificate, was the last person to perform maintenance on the engine. According to the Rolls-Royce maintenance manual, torque paint must be applied to all the rigid tube “B” nuts to ensure proper tightening. According to the maintenance manual, “failure to properly install, align, and tighten fuel, oil, and air fittings could result in an engine failure.”
On October 16, 2020, about 1515 eastern daylight time, a Bell 206B, N777CP, was substantially damaged when it was involved in an accident near Zephyrhills, Florida. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, about 15 minutes after departure, he heard a “binding sound” and felt a reduction in engine power and a slight nose left yaw. He checked his engine instruments and noted no illumination of annunciator lights or engine warnings. The low rotor rpm aural alarm then sounded, and he initiated an autorotation to swampy terrain. According to the Federal Aviation Administration inspector who responded to the accident site, the helicopter came to rest among pine trees and undergrowth. The tailboom was impact separated, and the main rotors were fractured about midspan. A detailed examination revealed the “B” nut at the engine fuel control unit was loose with no thread engagement. The nut was also missing the torque stripe markings on the line as required by the Rolls-Royce maintenance manual. During a test run of the engine, the “B” nut was tightened and torqued to proper specification. The engine ran smoothly and continuously at all power settings. A review of the helicopter’s maintenance records revealed the last annual inspection was completed about 75 hours prior to the accident. At that time, the Nos. 1 and 2 turbine wheels were replaced. The pilot also holds an airframe and powerplant certificate and was the last person to perform maintenance on the engine. According to the Rolls-Royce maintenance manual, torque paint must be applied to all the rigid tube “B” nuts and reapplied each time the nut is loosened and tightened. The manual states that “Proper tightening of the engine tubing connections is critical to flight safety. Failure to properly install, align, and tighten fuel, oil, and air fittings cold result in an engine failure.”
Improper torquing of the “B” nut at the fuel control unit, which led to a total loss of engine power and subsequent autorotation that resulted in substantial damage.
Source: NTSB Aviation Accident Database
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