What happened
On March 30, 2012, at approximately 18:40 EDT, a kit-built Zodiac CH 601XL, registration N8060J, departed from cruise flight and impacted a residential yard near Belmont, Ohio. The aircraft was being ferried from Mifflin County Airport (KRVL) in Pennsylvania to Spirit of St. Louis Airport (KSUS) in Missouri. The flight was being conducted under Visual Meteorological Conditions (VMC) with 10 miles of visibility.
Witnesses observed the aircraft in cruise flight when the engine appeared to stop and then restart, with one witness noting the engine roared loudly and sped up just before the aircraft nosed over. The aircraft's attitude dipped, leveled, and then entered a rapid descent, coming straight down into the ground. The pilot, a commercial pilot, was the sole occupant and sustained 1 fatal injury. The aircraft sustained substantial damage.
The investigation
Investigators examined the wreckage and found the impact was a near-vertical, high-energy event. The wings remained attached to the fuselage, and the engine and propeller were accounted for, though the wooden propeller blades disintegrated upon impact.
An examination of the Jabiru 3300a engine revealed several issues:
- Heavy sooting and contaminants were found in the carburetor inlet, the inlet side of the carburetor slide, and the butterfly valve.
- A varnish or gum-type buildup was present on the outlet side of the carburetor slide. The slide was found in the closed position and did not move freely without prying force.
- Sooting patterns on the engine-side components were consistent with a leaking intake valve, which can cause blowback into the intake manifold.
- There was a significant leak between the cylinder heads and cylinders on cylinder number six.
- A piece of filter material, similar to that from a NAPA 1394 oil filter, was found in the airflow divider.
Findings
Technical analysis suggested the engine likely experienced a loss of power. The presence of heavy sooting indicated that leaking intake valves could have caused blowback into the carburetor. Additionally, the excessive buildup on the carburetor slide could have caused it to stick in the open position; if the pilot reduced the throttle while the slide was stuck, the resulting overly rich mixture could have caused the engine to stop. The investigation also noted that the pilot's attention was likely diverted to managing the engine power loss, which led to the loss of aircraft control and the subsequent impact.