Accident Overview
On October 16, 2020, at about 1515 Eastern Daylight Time, a Bell 206B helicopter, registration N777CP, was substantially damaged in an accident near Zephyrhills, Florida. The pilot, who was the sole occupant, was not injured. The flight was conducted as a personal operation under Title 14 Code of Federal Regulations Part 91.
Pilot Report
According to the pilot, approximately 15 minutes after departure, he heard a "binding sound" and experienced a reduction in engine power accompanied by a slight nose-left yaw. The engine instruments showed no annunciator lights or warnings. Subsequently, the low rotor rpm aural alarm activated, prompting the pilot to initiate an autorotation into swampy terrain.
Aircraft Damage and Examination
The Federal Aviation Administration inspector who responded to the scene reported that the helicopter came to rest among pine trees and undergrowth. The tailboom was separated due to impact forces, and the main rotor blades were fractured near midspan.
Detailed examination of the engine revealed that the "B" nut at the engine fuel control unit was loose, with no thread engagement. The nut also lacked the required torque stripe markings specified in the Rolls-Royce maintenance manual. During a subsequent test run, the "B" nut was tightened and torqued to proper specifications, and the engine operated smoothly and continuously at all power settings.
Maintenance History
A review of the helicopter's maintenance records indicated that the last annual inspection was completed approximately 75 flight hours before the accident. At that time, the No. 1 and No. 2 turbine wheels were replaced. The pilot, who holds an airframe and powerplant certificate, was the last person to perform maintenance on the engine.
Maintenance Manual Requirements
According to the Rolls-Royce maintenance manual, torque paint must be applied to all rigid tube "B" nuts and reapplied each time the nut is loosened and tightened. The manual explicitly states: "Proper tightening of the engine tubing connections is critical to flight safety. Failure to properly install, align, and tighten fuel, oil, and air fittings could result in an engine failure."