CEN16LA061

The private pilot reported that, before departure, he performed an engine run-up with carburetor heat applied, and no anomalies were noted. The pilot departed for the personal local flight, and when the airplane reached about 100 ft above ground level, the engine power decreased from 2,400 to 1,600 rpm, so he executed a forced landing to a field. A postaccident examination of the airplane and engine revealed that the throttle body separated from the air intake manifold due to overload likely associated with impact. The fuel nozzle and primary venturi were missing from the carburetor and were not located. Although the engine could likely have started without these components installed, it is unlikely that it could have produced much more than idle power. Sliding marks on the sides of the throttle body revealed evidence of contact with the legs of the primary venturi. The contact marks had areas free of black deposits whereas areas adjacent to the marks were covered with deposits, indicating that a primary venturi had been installed until recently. The deposits on either side of the marks were not disturbed, indicating that the primary venturi did not rotate out of position; therefore, the primary venturi either fractured in service or was separated and lost from the throttle body after the carburetor was disassembled during the initial postaccident examination. The Federal Aviation Administration had previously issued an airworthiness directive (AD), which required that the accident make and model carburetor be inspected at each annual, 100-hour, or progressive inspection to determine if the primary venturi was loose or missing. According to the maintenance logbooks, the last inspection conducted in accordance with the AD occurred about 1.5 months and 1 flight hour before the accident. Although the weather conditions at the time of the accident were conducive to the formation of carburetor icing at cruise power, it is not likely that carburetor ice caused the venturi or fuel nozzle to break because the pilot had used carburetor heat during the run up and the engine was operating at takeoff power. The accident is consistent with a loss of engine power due to the carburetor's primary venturi, fuel nozzle, or both separating after takeoff. The reason for the separation could not be determined.

On December 11, 2015, about 1400 central daylight time, a Globe GC-1B airplane, N78067, conducted a forced landing into a field shortly after departure from the Lake Elmo Airport (21D), St. Paul, Minnesota. The private rated pilot and one passenger sustained minor injuries and the airplane sustained substantial damaged. The airplane was registered to Phoenix Flyers, LLC, Stillwater, Minnesota, and operated by a private individual under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed at the time of the accident and no flight plan was filed. The flight was originating at the time of the accident. The pilot reported that the engine start-up and run-up were "great" and no anomalies were noted; carburetor heat was tested during the run-up. The pilot initiated the takeoff and the airplane climbed to about 100 ft above ground level (agl) when the engine power decreased from 2,400 rpm to 1,600 rpm. The pilot maneuvered the airplane to the right to avoid trees and made a forced landing to a field. The pilot noted that carburetor ice might have caused the loss of engine power and he did not have time to apply carburetor heat after the loss of power. The pilot reported that the airplane had 1 hour of time in operation since the last annual inspection was accomplished on October 27, 2015. At 1353, the St. Paul Downtown Airport weather observation, located about 9 miles southwest of the accident site, recorded wind from 090 degrees at 8 knots, 10 miles visibility, overcast cloud layer at 1,600 ft, temperature 37° F, dew point 32° F, and altimeter setting 29.75 inches of mercury. The carburetor icing probability chart included in Federal Aviation Administration Special Airworthiness Information Bulletin No. CE-09-35, Carburetor Icing Prevention, indicated that the airplane was operating in an area that was associated with a serious risk of carburetor ice accumulation at cruise power settings. A Federal Aviation Administration (FAA) inspector performed a postaccident examination of the engine with the assistance of an engine mechanic. The examination revealed that the two-piece carburetor primary venturi was missing and subsequently could not be located during the course of the investigation. The carburetor was sent to the NTSB Materials Laboratory, Washington, DC, for an examination, which revealed that the throttle body was fractured at the intake manifold attachment flange consistent with overstress fracture of cast aluminum. The fuel nozzle was not located in the nozzle installation hole within the fuel bowl piece and no portion was located in the screw threads. Gaskets associated with the nozzle and the gasket between the fuel bowl and the throttle body were also missing. The primary venturi portion of the two-piece venturi was missing. Sliding contact marks with a lip of material were observed at three locations on the throttle body adjacent to the main venturi, corresponding tocontact with the three legs of the primary venturi. The contact marks had areas free of black deposits while areas adjacent to the marks were covered with deposits and the deposits on either side of the marks had not been disturbed. The interior of the air intake housing was viewed through the various available ports and none of the missing parts were found in the housing. According to a representative of the carburetor manufacturer, the engine would likely start without these components, but it was unlikely that the engine would make much more than idle power without the parts installed. Airworthiness Directive (AD) 98-01-06 According to AD 98-01-06, Precision Airmotive Corporation (now Marvel-Schebler Aircraft Carburetors) MA-3SPA carburetors with a two-piece venturi are to be inspected at each annual, 100-hour, or progressive inspection to determine if the primary venturi is loose or missing. According the maintenance logbooks, the last inspection per AD 98-01-06 that occurred before the accident was documented as accomplished on October 27, 2015.