Accident Details
On December 11, 2015, about 1400 central daylight time, a Globe GC-1B airplane, registration N78067, conducted a forced landing into a field shortly after departing from Lake Elmo Airport (21D) in St. Paul, Minnesota. The private pilot and one passenger sustained minor injuries, and the airplane sustained substantial damage. The airplane was registered to Phoenix Flyers, LLC, of Stillwater, Minnesota, and operated by a private individual under 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed, and no flight plan was filed. The accident occurred at the time of departure.
Pilot Report
The pilot reported that the engine start-up and run-up were "great" with no anomalies noted, and carburetor heat was tested during the run-up. During takeoff, the airplane climbed to about 100 feet above ground level (agl) when engine power decreased from 2,400 rpm to 1,600 rpm. The pilot maneuvered the airplane to the right to avoid trees and performed a forced landing to a field. The pilot noted that carburetor ice might have caused the loss of engine power and that he did not have time to apply carburetor heat after the power loss. The pilot also reported that the airplane had accumulated 1 hour of operation since its last annual inspection on October 27, 2015.
Weather Conditions
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, an overcast cloud layer at 1,600 ft, temperature 37°F, dew point 32°F, and an altimeter setting of 29.75 inches of mercury. The carburetor icing probability chart from Federal Aviation Administration Special Airworthiness Information Bulletin No. CE-09-35 indicated that the airplane was operating in an area associated with a serious risk of carburetor ice accumulation at cruise power settings.
Postaccident Examination
A Federal Aviation Administration (FAA) inspector, assisted by an engine mechanic, performed a postaccident examination of the engine. The examination revealed that the two-piece carburetor primary venturi was missing and could not be located during the investigation. The carburetor was sent to the NTSB Materials Laboratory in Washington, DC, for further examination. The examination 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 found in the screw threads. Gaskets associated with the nozzle and the gasket between the fuel bowl and 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 to contact with the three legs of the primary venturi. The contact marks had areas free of black deposits, while adjacent areas 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 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 to produce much more than idle power without the parts installed.
Airworthiness Directive
Airworthiness Directive (AD) 98-01-06 requires that Precision Airmotive Corporation (now Marvel-Schebler Aircraft Carburetors) MA-3SPA carburetors with a two-piece venturi be inspected at each annual, 100-hour, or progressive inspection to determine if the primary venturi is loose or missing. According to the maintenance logbooks, the last inspection per AD 98-01-06 before the accident was documented as accomplished on October 27, 2015.