The National Transportation Safety Board is pointing to the unseating of the carburetor metering jet and a lack of adequate carburetor maintenance instructions in the March 5 crash of a Ryan ST3KR piloted by actor Harrison Ford. Ford, a strong advocate for the general aviation industry, was seriously injured when his aircraft, N3178, crashed shortly after takeoff in Santa Monica, Calif. In the recently released probable cause, the NTSB said an improperly installed shoulder harness contributed to the severity of Ford’s injuries.
The Safety Board cited as the probable cause of the accident: “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.” The lack of adequate carburetor maintenance instructions was a contributor to the accident, the NTSB added.
Shortly after taking off, Ford alerted air traffic control that he had lost engine power. He made a left turn toward the airport, but soon realized he would not be able to reach it, the NTSB said. His aircraft struck a treetop and crashed into a nearby golf course. The investigation found the carburetor's main metering jet was unscrewed from its seat and rotated 90 degrees. This would have permitted increased fuel flow through the main metering orifice, producing an extremely rich fuel-to-air ratio, the NTSB said, adding this would have caused engine power loss. The Safety Board believes the jet gradually loosened from its seat over time, eventually causing it to rotate 90 degrees. The NTSB did not find any other mechanical issues that would have prevented normal operation.
The carburetor had been rebuilt about 17 years before the accident, but there were no pertinent instructions for the installation of the jet assemblies in the maintenance manual. Nor had there been any logbook entries found regarding carburetor maintenance.
Further, the NTSB noted the shoulder harnesses in the front and rear seats were not factory installed. They did not have reinforcement material or doublers around the attachment 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.”
The NTSB said it plans to work with the pilot community to stress the importance of carburetor maintenance and ensuring that shoulder harnesses are properly installed.