WPR13LA009 · Piper PA-38-112

After flying for about 1 hour, the pilot prepared the airplane for the landing approach. As he entered the downwind leg of the approach, the engine lost all power. Unable to restart the engine, the pilot performed a forced landing into an adjacent field, where the airplane sustained substantial damage. A wasp was found in the carburetor fuel bowl, and a wasp head was located wedged within the inner sleeve of the carburetor metering valve. The head was adjacent to the fuel channel hole, blockage of which would have resulted in a loss of fuel flow to the engine and subsequent loss of engine power. Both fuel tank vent ports were also found completely blocked with mud that was likely deposited by the wasp. However, the blocked fuel tank vent ports were unlikely to cause fuel starvation because fuel was present in all the supply lines and the fuel tanks were equipped with venting fuel caps, which were operational. The only path for a wasp-sized insect to access the carburetor fuel bowl was via the atmospheric bowl vent, the opening of which was located at the carburetor's air inlet. The vent leads directly to the fuel bowl and is wide enough for a wasp to pass through. The wasp most likely accessed the vent through either a hole in the air induction system, a gap in the carburetor-heat door seal, or through the carburetor-heat door opening (assuming the door had not been fully closed on the ground). It is not known when the wasp entered the fuel system. The airplane’s last annual inspection was performed about 2 1/2 years prior to the accident; however, it is unlikely the wasp would have been discovered during an annual inspection because the carburetor is not an inspection item. The insect would also be difficult to detect during preflight inspection.

Verbatim NTSB analysis and probable cause from the NTSB dataset