Accident Analysis: June Bug

June bugs, the thick-bodied, noisy beetles, aren’t the culprits, although they certainly leave a gory mess on windshields and leading edges. Accident reports that go beyond generic references to “insect remains” usually blame wasps for preventing airflow from reaching places it’s needed. The varieties known as mud daubers show a particular affinity for nesting in narrow passageways.

Sometimes those passages are inside pitot tubes, leading airspeed indicators to read inaccurately—or not at all. Few GA pilots train for this anomaly with any regularity. A student pilot who crashed a Cessna 172 in Santa Monica, California, had never practiced landing without an airspeed indication; not surprisingly, he crossed the threshold high and fast and didn’t go around until directed by the tower controller. A V-tail Beechcraft Bonanza owner aborted a takeoff when indicated airspeed wouldn’t increase past 60 knots, only to slide off the end of a wet grass runway. Wasps’ nests in pitot tubes also contributed to at least two fatal airline accidents.

More common—at least in the accident record—are insects crawling into fuel vents. In the past few years, they’ve caused engine stoppages in Cessna 150s and 172s, a Commander 112, and a Bell 47 helicopter. A wasp made it all the way into the float bowl of a Piper Tomahawk’s carburetor; its head was found blocking the metering valve. And numerous irregularities under the cowling of a Beech Musketeer that lost power just after takeoff included “a golf-ball-size mud dauber wasp nest in the carburetor throat…cast[ing] doubt on the thoroughness of the pilot’s preparations and preflight inspection.”

The inside of the carburetor isn’t a normal preflight item, but the pitot tube and fuel vents certainly should be. Blockages are usually close to the opening and not too hard to see, provided one really looks.