Boynton Beach, FL, USA
N281CB
BELL 206B
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.
HISTORY OF FLIGHT On November 11, 2008, about 0610 eastern standard time, a Bell 206B, N281CB, owned and operated by Aircoastal Helicopters, Inc., was substantially damaged when it impacted the ground during a forced landing. The helicopter departed Palm Beach County Park Airport (LNA), Lantana, Florida, about 0602. The certificated airline transport pilot and passenger received minor injuries. The flight was operated under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed at the time and no flight plan was filed for the local traffic report flight which was conducted for a local television station. According to the operator, the accident flight departed from LNA, climbed to approximately 1,000 feet above ground level (agl), flew to the south, and after a few minutes the helicopter was turned to fly northbound. Shortly after the completion of the turn, the helicopter yawed to the left and the low rotor and engine out warning systems activated. The pilot entered an autorotation, and achieved a normal rotor rpm. He then selected a landing site on a road within an industrial park; however, as the helicopter approached the intended landing area, the pilot noticed powerlines spanning across the road. The pilot was able to utilize the collective control to clear the powerlines, and impacted in a grass area along the road. PERSONNEL INFORMATION According to Federal Aviation Administration (FAA) records, the pilot, age 51, held an airline transport pilot certificate and a certificated flight instructor certificate each with a rating for helicopter. His most recent FAA second-class medical certificate was issued on November 13, 2007. According to the pilot he had accumulated 2,708 total hours of flight experience and 137 total hours of flight experience in make and model of helicopter. His last biennial flight review was completed on January 24, 2008. AIRCRAFT INFORMATION According to FAA records, the helicopter was manufactured in 1981 and issued an airworthiness certificate on April 16, 1981. The helicopter was equipped with an Allison 250-C20B series, gas-turbine engine. Airframe logbook entries dated October 9, 2008, indicated that the airframe had been inspected in accordance with the manufacturer's 100/200 hour inspections. Engine logbook entries dated November 8, 2008, indicated that the engine gearbox had been opened and inspected, with no defects found. The owner of the helicopter stated that the airframe had a total time in service of 12,540.70 hours and 12,391 total cycles. The engine had a total time in service of 14,420.70 hours. METEOROLOGICAL INFORMATION The 0619 recorded weather observation at Palm Beach International Airport (PBI), West Palm Beach, Florida, 10 miles north of the accident site; included winds from 060 degrees at 10 knots, few clouds at 2,600 feet agl, broken cloud layers at 4,100 feet agl, and an overcast cloud layer at 4,700 feet agl, 10 miles visibility, temperature 24 degrees Celsius (C), dew point 18 degrees C, and an altimeter setting of 30.02 inches of mercury. WRECKAGE AND IMPACT INFORMATION The helicopter was examined by an FAA inspector who responded to the accident site. The helicopter's tail boom was severed aft of the horizontal stabilizer, the landing skids and rear cross tube were damaged, the hull was damaged, the fuel cell was ruptured, and the smell of fuel was reported at the accident site. Engine continuity was verified through the driveshaft and continuity was confirmed through the engine to the compressor and was rotated through the starter generator. Tail rotor continuity was verified from the tail rotor forward to the separation, and flight control continuity was verified. Further examination revealed a loose pressure compressor (Pc) line from the power turbine governor to the fuel control unit and the "B"-nut was found loose to the point of no thread engagement. The wreckage was recovered by the owner and transported to the owner's hangar at LNA, under the supervision of an FAA inspector. The engine was subsequently removed from the helicopter, and sent to the engine manufacturer's facility for further evaluation. TEST AND RESEARCH The engine was examined at Rolls-Royce, Indianapolis, Indiana, on January 13, 2009, under the supervision of an FAA inspector. According to the FAA inspector, the engine was removed from the shipping container, and exhibited minimal damage. According to the Rolls-Royce engine investigation report, the "B"-nut was placed in the same manner in which it was found, with no thread engagement, the engine was started, warmed up, throttle was advanced to 65 percent N1, and remained at that cruise setting. Subsequently the engine experienced an uncommanded power reduction and decelerated to a sub-idle setting. A visual examination showed the "B"-nut had loosened and there was a gap between the Pc line and the "T"-fitting. The Pc line was reinstalled and "B"-nut tightened with the proper torque, restarted, and ran within production test standards. In the Rolls-Royce Operation and Maintenance manual section 73-00-00, Engine Fuel and Control System - Maintenance Practices, Fuel System Maintenance states, "Warning: Failure to properly install, align and tighten fuel, oil, and air fittings and tubes could result in an engine failure."
A loss of engine power due to an undertorqued air line fitting to the fuel control.
Source: NTSB Aviation Accident Database
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