Bell 206B N281CB accident near Boynton Beach, Florida

Probable cause

A loss of engine power due to an undertorqued air line fitting to the fuel control.

NTSB analysis

Approximately 8 minutes after the helicopter departed, the engine lost power and the pilot initiated an autorotation. To clear powerlines near the forced landing area, the pilot used collective to extend the helicopter's glide. The helicopter then touched down hard, severing the tail boom. Examination of the engine revealed that the "B"-nut for the pressure compressor (Pc) line from the power turbine governor to the fuel control unit was detached. Prior to an engine test run at the manufacturer's facility, the "B"-nut was placed in the same manner in which it was found at the accident site, with no thread engagement. The engine was started, warmed up, and throttle advanced to 65 percent N1. The engine experienced an uncommanded power reduction and decelerated to a sub-idle setting. A visual examination showed that the "B"-nut had loosened entirely and there was a gap between the Pc line and the "T"-fitting. After the Pc line was reinstalled and the "B"-nut was tightened with the proper torque, the engine was restarted and ran within production test standards. The Rolls-Royce operation and maintenance manual gave a warning that "failure to properly install, align and tighten fuel, oil, and air fittings and tubes could result in an engine failure." On November 8, 2008, an entry in the engine logbook indicated that the engine gearbox had been opened and inspected this process required the "B"-nut to be loosened and the lines separated to access the gearbox.

Text from the NTSB. Open the NTSB docket for ERA09LA047 for the full record.