LAKELAND, FL, USA
N902BA
AEROSPATIALE AS-350
THE PILOT-IN-COMMAND WAS MANEUVERING BETWEEN 500 TO 600 FEET AGL, AT 70 MPH, WHEN THE HELICOPTER EXPERIENCED A HIGH SIDE GOVERNOR FAILURE. HE RETARDED THE FUEL CONTROL LEVER (F.F.C.) AFT TO THE FLIGHT IDLE POSITION AND NOTED NO CHANGE. HE THEN MOVED THE THROTTLE TO THE OFF POSITION, TURNED THE FUEL CONTROL VALVE OFF, AND MADE A FORCED LANDING IN AN OPEN FIELD WHILE MANEUVERING IN THE DESCENT TO AVOID POWER LINES. THE HELICOPTER ROLLED OVER ON ITS LEFT SIDE DURING THE LANDING. EXAMINATION OF THE ENGINE BY THE FAA AND THE ENGINE MANUFACTURER CONFIRMED THE PILOT'S DIAGNOSIS OF A HIGH SIDE GOVERNOR FAILURE. THE EMERGENCY PROCEDURE IN THE FLIGHT MANUAL FOR A GOVERNOR FAILURE STATES, SLOWLY MOVE THE F.F.C. LEVER REARWARDS UNTIL ROTOR SPEED CORRESPONDS TO A POSITION OF THE INDICATOR POINTER IN THE CENTER OF THE GREEN AREA. THE MANUAL DOES NOT STATE THAT IN ORDER TO MODULATE THE FUEL FLOW, THE F.F.C. LEVER MUST GO BELOW THE FLIGHT IDLE POSITION.
On January 13, 1994, about 1230 eastern standard time, a Aerospatiale AS350, N902BA, registered to Bulldog Airlines Inc., crashed in Lakeland, Florida, while operating as a 14 CFR Part 91 aerial observation flight. The helicopter was destroyed. The commercial pilot sustained a serious injury, and the passenger sustained a minor injury. Visual meteorological conditions prevailed and a company flight plan was filed. The helicopter departed from Orlando, Florida, about 40 minutes before the accident. The pilot stated after completing a turn to the west between 500 to 600 feet agl, at 70 mph, he experienced a high side governor failure. He heard an increase in engine rpm and the helicopter yawed to the left. He retarded the fuel control lever aft to the flight idle position, and noted no change, moved the throttle to the off position, turned the fuel control valve off, entered autorotation, and made a Mayday call. High tension wires were observed to his front, he increased collective pitch and applied aft cyclic in order to clear the wires. The rotor rpm decreased, and collective pitch was lowered in an attempt to regain rotor rpm. The pilot increased collective pitch as the helicopter collided with the terrain, and rolled over on its left side. Examination of the airframe and flight controls was conducted by American Eurocopter Corporation in the presence of the FAA. There was no evidence to indicate a precrash mechanical failure or malfunction. The engine was shipped to Textron Lycoming, Stratford, Connecticut, and ran in an engine test cell in the presence of the FAA. The engine was started and accelerated to ground idle (50% Ng). The engine continued to accelerate beyond 50% Ng without throttle advancement. The engine was manually shut down after reaching 90% Ng. The fuel control and fuel pump were removed and replaced with a slave set-up. The engine was started and satisfactory engine operation up to takeoff power was demonstrated. Disassembly of the fuel control and fuel pump revealed the fuel control bearing had failed and the drive coupling between the fuel pump and fuel control was sheared. Textron Lycoming concluded: a. The reported increase in Ng and Np was caused by a fuel control malfunction. b. The fuel control malfunction was determined to be failure of the fuel control drive shaft bearings. c. The failure mode of the bearings is indicative of dilution of the blue-grease which causes accelerated bearing wear. d. The exact cause for the blue-grease dilution could not be conclusively determined. For additional information see Summary of Test, Engine Test Report No: 360094.9C, and Investigation Report of LTS101-600A-2 Engine, Serial Number LE43515. These reports and the disassembled fuel control and fuel pump were forwarded to the NTSB Laboratory for further analysis. Examination of the fuel control driveshaft bearing assemblies by the NTSB Materials Laboratory revealed bearing separations in the inner races and inner spacers of the bearing assemblies. The outer races and bearing balls for both bearings were separated from the driveshaft, and the outer spacer section was stuck axially to the outer bearing race. The bearing cages could be manipulated rotationally and axially along the driveshaft area, but could not be switched axially relative to each other. A deformed circular disk believed to be the dust seal normally located on the aft side of the outer bearing was located aft of the bearing cage. The inner raceways and spacers with the seal and cages shifted allowing unobstructive viewing of the components. The outer bearing inner race contained little damage and the surface finish appeared to be original. The inner spacer had a circumferential groove just forward of the outer bearing inner race consistent with the bearing balls rotating circumferentially on the spacer in the single axial path. The inner bearing inner race contained deposited material on its surface, but its overall shape appeared to be of a typical raceway. Numerous thin shims were noted between the inner bearing outer inner race and the fly-weight area. The outer races and outer spacers disclosed similar features as that found on the inner components. The outer bearing outer race contained little damage and the surface finish appeared to be original. The inside diameter surface of the outer spacer had a circumferential groove near the outer bearing and indications of additional grooving forward of this position. The inner bearing outer raceway contained deposited material on its surface, but its overall appearance appeared to be of a typical raceway. Microscopic viewing of the inner bearing cage disclosed heavy rotational wear on the inside and outside diameter, and the cage was cracked. The outer bearing cage was worn around each ball pocket on the outer diameter, and circumferentially around the crown base. The crown base was fractured at the minimum width section between a pocket and the crown base. The extension of the driveshaft forward of the fly-weight support was cracked in the radius, indicative of a fresh overstress fracture. (For additional information see NTSB Metallurgist's Factual Report.) The flight manual for the AS 350 D, Section 3, Emergency Procedures states: C. GOVERNOR MALFUNCTION 2) Excessive fuel flow rate: NG, t4 NR and torque increase * Do not reduce collective pitch. * Slowly move the F.F.C. lever rewards until rotor speed corresponds to a position of the indicator pointer in the center of the green area. * Continue flight with the governor out of action. Any reduction of collective pitch will cause an increase in rotor speed which must be counteracted by adjusting the F.F.C. lever position. * The landing approach should be made along a low gradient path, at 65 knots (75 MPH) IAS holding the rotor at 390 r.p.m. by F.F.C. lever action. * In final approach, reduce forward speed without touching the F.F.C. lever; rotor r.p.m. will fall off with deceleration to a low speed touch-down. The NTSB investigator-in-charge, mailed a letter on June 14, 1994, to Allied Signal Aerospace Engine System & Accessories, and American Eurocopter Corporation, inquiring about the emergency procedures listed in the flight manual for governor malfunction, and possible additions to the emergency procedure. In addition both companies were asked to explain why the pilot did not notice a change when he moved the F.F.C. lever rearward, and why he was not able to maintain manual control of the governor and engine rpm. Allied Signal Aerospace Engine System & Accessories replied to the letter on July 18, 1994. They stated, a drive bearing failure would allow the governor lever to close off the Py orifice. Py pressure would increase thus increasing fuel flow and N1 speed. The pilot did not notice any change because the throttle lever was not rotated below the flight idle position. To modulate fuel flow one must go below flight idle on the F.F.C. All questions concerning additions to the emergency procedure were deferred to American Eurocopter Corporation. A subsequent letter was sent to American Eurocopter Corporation on June 24, 1994, with Allied Signal Aerospace Engine System & Accessories response. American Eurocopter Corporation stated in a fax dated August 3, 1994, that they did not understand why the pilot was unable to reduce the engine rating when he moved the fuel control lever from the flight detent to the stop detent. They further stated the probable causes are a faulty FCU cut off valve operation, or discontinuity in the control between the fuel control lever and the FCU. Textron Lycoming stated on August 4, 1994, that they did not observe a failure or malfunction of the FCU cut off valve or note any discontinuity in the control between the fuel control lever and the FCU. American Eurocopter Corporation deferred all questions concerning additions to the emergency procedures to their Flight Test Department. The fuel control and fuel pump were released to Mr. Michael Barrett, United States Aviation Underwriters Inc., Orlando, Florida, on June 14, 1994.
THE PILOT-IN-COMMAND'S FAILURE TO FOLLOW THE EMERGENCY PROCEDURE IN THE FLIGHT MANUAL FOR GOVERNOR MALFUNCTION. CONTRIBUTING TO THE ACCIDENT WAS INADEQUATE WRITTEN PROCEDURES IN THE FLIGHT MANUAL BY THE AIRCRAFT MANUFACTURER.
Source: NTSB Aviation Accident Database
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