Bow, NH, USA
N407GB
BELL 407
Two days before the accident, the helicopter landed at an airport due to en route snow. On the day of the accident, company personnel spent about 5 hours cleaning and deicing it. The pilot subsequently conducted multiple ground and air taxi runs before departing toward his home heliport. About 45 minutes into the flight, when the helicopter was about 900 feet over tree-covered terrain, the engine lost power. The pilot then performed an approximately 180-degree autorotation to a curved street. The helicopter landed hard and sustained substantial damage to the fuselage. Prior to the loss of engine power, the pilot did not observe any caution or warning lights, and the FADEC (Full Authority Digital Engine Control) remained in the automatic mode. The pilot also noted no unusual noises or yawing of the helicopter prior to the loss of engine power. A subsequent download of the helicopter's incident recorder revealed "Engine Flameout," "Nr Droop," and "Ng Exceedance Low" faults. It also indicated that when the flameout detection occurred, "Fuel Enable" and "Auto Relight" functions became active. Subsequent examinations of the airframe, including the fuel supply system, revealed no anomalies that would have resulted in a flameout. The electronic control unit was downloaded, with no faults noted. The electronic control unit and the hydro mechanical unit were examined with no anomalies noted. The engine was mounted in a test cell and successfully run with no discrepancies noted. During a later engine test run, the fuel was intentionally shut off through a solenoid, and except for rotor rpm, the incident recorder indicated the same faults as noted in the accident sequence, confirming that the loss of engine power likely occurred due to an interruption of fuel flow for undetermined reasons.
On December 22, 2008, at 1604 eastern standard time, a Bell 407, N407GB, operated by JBI Helicopter Services, was substantially damaged during a forced landing in Bow, New Hampshire. The certificated commercial pilot was seriously injured. Visual meteorological conditions prevailed. The helicopter was operating on a company visual flight rules flight plan between Danielson Airport (LZD), Danielson, Connecticut, and Brigham Heliport (NH33), Pembroke, New Hampshire. The positioning flight was conducted under 14 Code of Federal Regulations Part 91. According to a representative of the operator, the helicopter departed its home base in Pembroke on December 18th, about 1200, embarked a passenger in Somerville, Massachusetts, and continued to Old Lyme, Connecticut, to drop off the passenger. About 3 miles from Old Lyme, the weather started to deteriorate in falling snow to a visibility of approximately 2 miles. After dropping off the passenger, the pilot started back toward Pembroke, but due to the weather, decided to land at an en route heliport and remain overnight. The following day, the pilot was able to fly to Danielson, but again decided to land and wait for better weather. For the following 2 days, the weather remained questionable, and the pilot did not fly. On the day of the accident, the director of maintenance and a relief pilot (the accident pilot) drove to Danielson. Upon arrival, they found that where the sun was shining on the helicopter, it was free of snow and ice. The areas of the helicopter that had not melted were brushed off, and any trace of ice was removed using isopropyl alcohol. Windshield washer fluid was also attempted because of its non-toxic and non-corrosive properties; however, the isopropyl alcohol worked better. The total time spent removing ice was approximately 4.5 to 5 hours, which included a "very thorough" pre-flight inspection. After the cleaning and preflight inspection, the pilot started the helicopter and completed a ground run to make sure all systems were normal, which they were. The pilot then decided to shut down the helicopter and perform another preflight inspection. A second start was subsequently accomplished, and the helicopter was taxied to the tarmac area and shut down to take on fuel from the service truck. After taking on approximately 60 gallons of fuel, the pilot started the helicopter once again and hover-taxied along the taxiway to ensure all systems were operating and up to temperature. According to the pilot, the helicopter departed Danielson at 1518. About 3 1/2 miles southwest of Pembroke, at 1,400 feet above mean sea level, the engine, a Rolls Royce 250-C47B, experienced an uncommanded shutdown. GPS plotting revealed that the helicopter was flying over tree-covered terrain, then completed an approximately 180-degree autorotation to a curved, tree-lined street, landing on an estimated heading of about 150 degrees magnetic at an elevation of about 500 feet. Weather, reported at an airport about 3 miles to the north, at 1551, included clear skies, visibility 10 statute miles, winds from 280 degrees true at 13, gusting to 24 knots, temperature -7 degrees Celsius, dew point -15 degrees Celsius, and an altimeter setting of 29.84 inches of mercury. Prior to the engine shutdown, the pilot observed no caution or warning lights, and the FADEC (Full Authority Digital Engine Control) remained in the automatic mode. The pilot also noted no unusual noises or yawing of the helicopter prior to the shutdown. Following the accident, inspectors from the Federal Aviation Administration (FAA) Portland Flight Standards District Office conducted an on-scene examination of the helicopter. The inspectors invited an investigator from the insurance company, who also owned a helicopter company, to participate in the examination. The investigator produced a written report, which included: No obvious fuel or oil leaks were found. Total fuel onboard was 439 pounds with 201 pounds in the auxiliary fuel tank. The fuel shut-off valve was found in the closed position; however, local fire personnel indicated that they had shut off the fuel valve per their training. The main fuel filter had fuel in it, there was no contamination found, and the bypass had not activated. Fuel pressure was confirmed on both the left and right fuel boost pumps. The engine was motorized, and fuel was confirmed through the fuel nozzle. The Combined Engine Filter Assembly (CEFA), which included an engine fuel filter and an engine oil filter, did not exhibit any evidence of bypass. There was no evidence of unburned fuel or fuel droplets in the soot aft of the exhaust pipe. No obstructions or debris were found in the particle separator, and the snow baffles were properly placed and secure. The pilot’s throttle was found in the FLY position. The helicopter was subsequently powered up, and the FADEC caution lights indicated “Restart Fault” and “FADEC Degraded,” which was consistent with the engine spooling down with the throttle in the FLY position. The investigator downloaded the maintenance section of the FADEC, with the only fault being an “open metering valve warning,” which was consistent with the engine being shut down or power was removed when there was either N1 speed or the throttle was open. A representative of the operator was also on scene, and noted "heavy undercarriage damage," and that the tail boom had sustained bending in an upward direction, consistent with stinger contact with the ground at impact. The helicopter was later moved to the insurance investigator’s facility for storage, pending further examination. A representative from Rolls Royce subsequently determined that three “triggers” were noted in the helicopter’s Incident Recorder (IR): Engine Flameout Detected, Nr Droop Detected, and Ng Exceedance Low Detected. It also indicated that when the flameout detection occurred, Fuel Enable and Auto Relight functions became active. The Electronic Control Unit (ECU) memory data was also downloaded, and no FADEC system faults were noted. On January 21, 2009, a general examination of the wreckage was conducted under NTSB oversight. During the examination, tail rotor and main rotor drive continuity were confirmed. The helicopter’s electrical system was energized via battery, and 450 pounds of fuel were indicated. The fuel boost pumps were energized, with the resultant fuel pressures indicating within the “green” band. The throttles were rotated from off, to idle, to full on, and the corresponding hydro mechanical unit (HMU) positions confirmed proper rigging. Upon reexamination, small particles were found in the main fuel filter canister and within the filter paper folds. Some very small metallic particles in the canister were captured along with other particulates in a coffee filter. A magnet passed under the coffee filter revealed that the particles were not magnetic On March 3, 2009, the engine was test run at Rolls Royce facilities under NTSB oversight. After the engine was started, and allowed to warm up, it was taken through a series of accelerations and decelerations where it performed within production standards. It was then taken through a five-point calibration check, and found to meet or exceed specification power. The engine was then shut down normally. The engine was subsequently restarted for testing of the ECU overspeed system. After engine stabilization, the overspeed test switch on the test cell was engaged, and the engine continued to run normally, as designed. A shutoff solenoid was attached to the fuel line, and subsequently, the engine was started and allowed to stabilize for 2 minutes. The shutoff solenoid was then activated, which shut the engine down. Except for rotor rpm, IR data was identical to that which was recorded when the engine shut down on the accident flight. On March 17, 2009, the helicopter fuel system was further examined under FAA oversight. The FAA inspector did not provide examination results; however, representatives from Rolls Royce and the operator reported that the main and auxiliary fuel cells were clean, and absent of debris. Both the forward and rear boost pumps were removed and functionally checked. While both were found to operational, the “B” nut securing the pressure line on the forward pump was found to be cracked. However, the quantity of fuel remaining would have covered the cracked nut. The representative from Bell Helicopter also noted that "magnetic metallic debris was found in a check valve that was found in a stuck open position," but indicated that neither the debris nor the cracked "B" nut would have resulted in the engine shutdown. Examinations were subsequently conducted of all fuel lines with no anomalies noted. The fuel shutoff solenoid was then repeatedly cycled, with no discrepancies noted. On June 11, 2009, the investigative team met at Goodrich Pump and Engine Controls (GPECS) to examine the HMU and the ECU. The ECU was subjected to “standard environmental stress screen testing” that included 5 minutes of vibration, followed by nine cycles of thermal testing. All testing passed, except for the torque sensor input accuracy during temperature testing. HMU electrical component and continuity checks yielded no anomalies. Fuel flow schedules in both the automatic and manual modes were within new-unit limits. A complete acceptance test was performed, which yielded test points were within new-unit or service limits. The pump and metering unit were subsequently disassembled, and no unusual wear, contamination, loose items, or other anomalies were noted.
An interruption of fuel flow for undetermined reasons, which resulted in an engine flameout.
Source: NTSB Aviation Accident Database
Aviation Accidents App
In-Depth Access to Aviation Accident Reports
