WPR15FA121

A total loss of engine power during initial climb when the carburetor main metering jet became unseated, which led to an extremely rich fuel-to-air ratio. Contributing to the accident was the lack of adequate carburetor maintenance instructions. Contributing to the severity of the pilot's injuries was the improperly installed shoulder harness.

Shortly after takeoff, the pilot advised the air traffic control tower controller that the engine had lost power, and the pilot requested an immediate return to the airport. The pilot initiated a left turn toward the airport; however, during the approach, he realized that the airplane was unable to reach the runway. Subsequently, the airplane struck the top of a tree and then impacted the ground in an open area of a golf course. A postaccident examination of the airplane's engine revealed that the carburetor's main metering jet was unscrewed from its seat and rotated 90 degrees. The unseated jet would have allowed an increased fuel flow through the main metering orifice, producing an extremely rich fuel-to-air ratio, which would have resulted in the loss of engine power. It is likely that, over time, the jet gradually loosened from its seat, which allowed it to eventually rotate 90 degrees. No further mechanical failures or malfunctions were revealed that would have precluded normal operation. A review of the airplane's maintenance records indicated that the carburetor was rebuilt during the airplane's restoration about 17 years before the accident. The carburetor maintenance instruction manual contained no pertinent instructions for the installation of the jet assemblies. Further, no maintenance entries in the engine logbook regarding carburetor maintenance were found. Had the carburetor maintenance instruction manual identified a means to ensure the security of the main metering jet, it is unlikely that the jet would have become unseated. There was no record of maintenance personnel inspecting the carburetor jets during the previous 17 years nor was there a requirement to do so. The front and rear seats of the airplane were equipped with non-factory-installed shoulder harnesses. The pilot's shoulder harness was installed by mounting the end of the restraint to the lower portion of the seatback assembly, which was made of thin aluminum. No reinforcement material or doublers were installed at or around the attachment bolt hole in the seatback. The lack of reinforcement allowed the attachment bolt, washers, and stop nut to be pulled upward and through the seatback structure during the impact sequence, which resulted in the pilot's loss of shoulder harness restraint. It is likely that the improperly installed shoulder harness contributed to the severity of the pilot's injuries. As a result of this investigation, the NTSB is working with the pilot community to inform them of the lessons learned from this accident: the security of the carburetor's main metering jet and the security of the shoulder harness are both critical aspects of aviation safety.

According to FAA recorded communications, the SMO air traffic control tower local controller reported that, at 1419, the pilot requested a departure from runway 21 for left closed traffic. The pilot was cleared for takeoff about 1 minute later. About 1 minute after takeoff, the pilot radioed that he had an engine failure and requested immediate return. The controller cleared the pilot to land on runway 21; the pilot responded with a request for runway 03. The controller subsequently cleared the pilot to land on runway 03 and then issued the wind information. There was no further transmission from the pilot after 1422. According to the FAA Digital Airport/Facility Directory, SMO is a continuously operated towered airport with a field elevation of 177 feet. The airport was equipped with one asphalt runway, runway 03/21 (4,973 ft long by 150 ft wide). Investigative personnel noted that the approach end of runway 03 of the airport was positioned on a plateau about 75 ft higher than the accident site. Airframe Examination Both the left and right wings were removed to facilitate wreckage recovery and subsequent transport. During postaccident examination, the airframe fuel filter (gascolator) was removed and subsequently disassembled. The gascolator bowl was free of debris. A very slight amount of debris was observed on the gascolator screen. Multiple fuel line fittings were impact damaged, and separated from the gascolator. The fuel selector valve handles (forward and aft) were found in the "off" position. The fuel selector valve remained attached and secure to the selector valve handle shaft. The fuel selector valve was removed and disassembled. Internal examination of the fuel selector valve revealed that the valve was in the "off" position. Air was applied to the inlet port, and when the valve was moved to both the main and reserve positions, no restrictions were noted. The fuel tank remained intact, but the fuel tank cap was separated. Impact damage was observed surrounding the fuel cap. Internal examination of the fuel tank revealed that no debris or contaminants were present. No fuel was observed within the fuel tank. Compressed air was applied to the main and reserve outlet port fuel lines and the fuel vent line, and no restrictions were noted. Examination of the aft cockpit seat revealed that the left and right seatbelt restraints remained attached to their respective mounts and seat structure. The shoulder harnesses were separated from the seat back assembly, but the attach bolt remained intact and secure to the shoulder restraint harness. The shoulder harness was attached using a bolt, two washers, and an elastic stop nut. A hole, similar to the size of the shoulder harness attach bolt, was observed on the back of the seat, about 2-3/8 inch above the seat bottom. The aluminum structure of the seat back was peeled away (outward and upward) from the shoulder harness bolt hole, consistent with the attach bolt being pulled through the metal structure. There was no evidence of reinforcement surrounding the shoulder harness bolt hole and the peeled away seatback structure. Engine Examination Examination of the recovered Kinner R-55 engine, serial number 07450, revealed that it remained attached to the airframe engine mount and was displaced downward at an approximate 45-degree angle. The starter was separated from the starter adapter, and the carburetor was displaced from its mounts. Impact damage was observed on the bottom side of the oil tank, and the outlet port was damaged and pulled away at the fitting, which resulted in a breach of the oil tank. When the engine was attached to an engine hoist, residual oil was observed draining from the oil tank outlet port. The oil shutoff valve was found separated from the oil tank outlet fitting and the associated oil line tubing. The oil shutoff valve was found in the open position, and the handle was bent, consistent with impact damage. When actuated by hand, the oil shutoff valve actuated normally between the open and closed positions. Several fuel and oil lines were found impact damaged and separated. The oil drain valve was intact and in the closed position. The forward spark plugs on all five cylinders were removed. Both the left and right magnetos were also removed. The propeller was rotated by hand, and thumb compression was obtained on cylinder Nos. 1, 2, 4, and 5. All intake and exhaust rocker arms for all cylinders exhibited equal lift action. Damage to the No. 3 cylinder intake and exhaust push rod tubes resulted in a decreased clearance for the intake and exhaust valve rocker arms (0.004 inch and 0.002 inch, respectfully). Both of the intake and exhaust valve rollers would not rotate. The valve clearance adjustment nut was loosened, which allowed for further movement of the intake and exhaust valve rocker arms. The propeller was then rotated by hand, and thumb compression was obtained on the No. 3 cylinder. When the propeller was rotated, no internal binding or friction was noted within the engine and valve train. The Holley 419 carburetor was found separated from its mounts. The mounting flange and a portion of the carburetor casing around the throttle valve/plate were separated. All safety wire were intact and secure. The carburetor was disassembled and examined. The fuel screen was intact and free of debris. The float bowl was free of debris and contained no residual fuel. The metal float was intact and free of damage. Compressed air was applied to the inlet port of the carburetor, and the float and needle valve were actuated with no anomalies noted. Solvent was poured into the float bowl and the accelerator pump was actuated; fuel was observed expelling from the nozzle. All internal components of the carburetor appeared to be intact and undamaged. The main metering jet cover was removed from the housing at the bottom of the carburetor. The main metering jet was found unscrewed from its seat and rotated laterally about 90 degrees. The internal cap, main metering jet, and seat appeared to be bright in color and polished. Portions of the jet threads appeared to be rounded off. No gasket was observed within the main metering jet housing. In addition, no evidence of thread locking compound was observed on the threads of the main metering jet or the threads of the seat. According to the 1943 Holley Aircraft Carburetors Instruction Manual for Models 419 and 429, the actual metering of the fuel is accomplished by the main metering jet located in the passage between the discharge nozzle and the float chamber. The metering system provides a constant mixture ratio over the cruising range of engine operating speeds. A review of the maintenance logbooks revealed that an extensive restoration of the airplane and engine overhaul was completed on May 21, 1998. At the time of the accident, the airframe and engine had accumulated approximately 169 hours since the restoration. An entry stated that a new float and gasket were installed in the carburetor during this time. The airplane was issued a standard-normal airworthiness certificate on June 4, 1998. Review of the Holley Aircraft Carburetors Instruction Manual for Models 419 and 429, revealed that there were no pertinent instructions regarding the installation or continued maintenance of the jet assemblies. Further, no maintenance entries were located in the engine logbook regarding carburetor inspections since the overhaul. For further details of the airframe and engine examination, see the NTSB Airframe, Engine, and Maintenance Records Examination Summary Report within the public docket for this accident. The postaccident examination of the airframe and engine revealed no additional evidence of a mechanical malfunction that would have precluded normal operation. Review of Advisory Circular (AC) 21-34, dated June 4, 1993, provides basic principles regarding design and installation of combined shoulder harness and saf