Pilot Debrief

GLOBE GC 1B near Lake Elmo, MN — 2015-12-11

Final reportCEN16LA061
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Date
2015-12-11
Location
Lake Elmo, MN, USA
Airport
21D
Aircraft
GLOBE GC 1B
Registration
N78067
Category
Airplane
Highest injury
Minor
Fatalities
0
Phase of flight
Takeoff roll

Probable cause

A loss of engine power due to the carburetor’s primary venturi, fuel nozzle, or both separating after takeoff.

NTSB narrative

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.

Analysis

Primary failure mode
Engine power loss
First missed decision gate
Apply carburetor heat immediately after engine power loss.

NTSB coding

Evidence available

  • Photos
  • 9 docket documents
View NTSB final reportView NTSB docket

Docket documents9

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