Corona, CA, USA
N4309E
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.
HISTORY OF FLIGHT On October 13, 2012, about 1215 Pacific daylight time, a Piper PA-38-112, N4309E, collided with terrain following a loss of engine power during landing at Corona Municipal Airport, Corona, California. The pilot/owner was operating the airplane under the provisions of 14 Code of Federal Regulations Part 91. The commercial pilot sustained minor injuries. The airplane was substantially damaged during the accident sequence. The local flight departed Corona about 1115. Visual meteorological conditions prevailed, and no flight plan had been filed. The pilot reported that during the landing approach he performed his pre-landing checks, and that shortly after turning on the auxiliary fuel pump, the engine lost all power. He performed troubleshooting procedures, with no increase in engine power. The airplane was on the left downwind leg of runway 07, and the pilot was concerned that he did not have enough altitude to turn towards the runway; he elected to land the airplane in a field directly ahead. During the approach, the right wing struck a tree, and the airplane descended underneath a power line, striking the airport perimeter fence and coming to rest in a field. The airplane sustained substantial damage to the right wing, firewall, and tailcone during the accident sequence. AIRCRAFT INFORMATION The low-wing, single-engine airplane, was manufactured in 1978, and equipped with a Lycoming O-235-L2C engine, serial number L-16453-15. Maintenance records indicated that the engine was overhauled and installed on the airplane in 2004. At the time of the most recent annual inspection, dated March 3, 2010, the engine had accrued a total flight time of 115 hours since overhaul. At that time, the airframe had accrued 2,021 flight hours. The engine tachometer indicated 2,075.06 hours at the accident site. The pilot reported that he kept the airplane stored at an outdoor tie-down spot at Corona Airport. TESTS AND RESEARCH Fuel Supply System Aircraft recovery personnel reported draining about 2 gallons of fuel from the left tank during the recovery operation. The right tank was breached, and a 6-foot-long by 2-foot-wide stain was present on the ground surrounding the tank. During the subsequent airframe examination by the National Transportation Safety Board (NTSB) investigator, an additional 2 gallons of fuel was observed in the left tank. The fuel lines from the tanks to the carburetor inlet were full with fuel and free of obstruction. The gascolator bowl was full of light-colored fluid consistent in color and odor with aviation gasoline, and its filter screen was free of debris. The fuel selector valve was observed in the right tank position. The valve could be moved through its detents by hand, but crumpled airframe structure had become impinged against the selector shaft, preventing smooth operation of the handle. The electrically driven fuel pump issued fuel when engaged. Examination of the wing tank vent ports, located underneath each wing, revealed that they were completely plugged by a mud-like substance. The ports were removed, and the obstruction appeared consistent with Mud Dauber (wasp) debris. The fuel tank filler caps were of the vented type. Examination revealed that the vent flapper valve was intact, and that the vent opened appropriately with the application of low air vacuum. Carburetor The Precision Airmotive Carburetor, model MA-3A, remained undamaged, and firmly attached to the intake manifold. The fuel mixture, throttle, and carburetor heat linkages were intact and continuous to their respective cabin controls, and moved smoothly when operated. The airbox and filter assembly sustained crush damage. Although the forward surface of the filter element was coated in a wax-like substance, the filter was able to pass air when blown. The fuel inlet screen was free of debris. The carburetor was removed and opened for examination. The bowl was about half full with clear, blue-colored fuel. The float was of the brass type, and appeared intact and free of leaks. The float valve was intact, pliable, and along with the valve seat, free of contamination. A wasp-like insect was at the bottom of the bowl, adjacent to the bowl drain plug and mixture metering sleeve. Further examination of the metering valve revealed the head of a wasp-like insect wedged within the valves inner sleeve. The position of the head was adjacent to the fuel channel hole in the carburetor body. The design of the carburetor bowl allows for two direct paths to atmospheric pressure. The first is the drain plug, which, when removed, allows fuel to be drained through two, 3/32-inch-wide drain channels. The second path is that of the atmospheric bowl vent. The opening for this vent is 1/4-inch-wide, and located at the carburetor air inlet, adjacent to the throttle flange, and upstream of the fuel nozzle outlet. The vent channel continues through the carburetor body, and into the roof of the fuel bowl, where it reduces in size to a 3/16-inch orifice. Carburetor induction air enters a chin scoop intake in the lower airbox cowling, and flows directly through the filter, and into the carburetor airbox. The airbox incorporates a positive shut off (door) heat intake, so that when carburetor heat was selected, unfiltered induction air was drawn through a hose attached to a muffler shroud. Engine The engine sustained minimal damage during the accident sequence, and post impact examination did not reveal any anomalies that would have precluded normal operation.
Total loss of engine power during the landing approach due to insect debris in the carburetor metering valve, which resulted in fuel starvation.
Source: NTSB Aviation Accident Database
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