On April 4, 2024, about 2000, a Kitfox Series 5, N743JT, was substantially damaged when it was involved in an accident near Yucca Grove, California. The experimental, amateur-built airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot was relocating the airplane from California to Colorado, and this was the first leg of the trip. He departed from Cable Airport (CCB), Upland, California, with a destination of Henderson, Nevada.

While en route at an altitude of 9,500 ft mean sea level, the pilot noticed a slight reduction in engine oil pressure. With no increase in oil temperature or other engine warnings he decided to continue the flight while monitoring the engine parameters. The engine appeared to be operating normally, but a short time later the oil pressure began to drop at a faster rate. He decided to perform a precautionary landing rather than risk continuing the flight towards inhospitable terrain as the sun began to set.

He shut down the engine and configured the airplane for landing on a highway service road, but while on approach he noticed the landing area was obstructed by light poles. He maneuvered the airplane towards an adjacent dirt field; however, the terrain was much rougher than anticipated, and the airplane nosed over during roll out after striking scrub brush.

The airplane sustained damage to both wings and the vertical stabilizer, and post-accident examination revealed the belly of the airplane was completely covered in engine oil.

The airplane was equipped with a Continental C90 engine that was fitted with a steel “kidney” style oil sump. Examination of the engine compartment revealed that the oil sump and surrounding components and fittings, including the back side of the carburetor, were coated in oil. No anomalies were noted to the engine oil system lines, filter, or cooler. The oil drain plug remained in place and closed. One quart of oil was drained from the sump; the oil was brown in color, and free of visible debris.

A 3-inch-wide bead of grey filler had been applied to the forward neck of the oil sump mounting flange. When the sump was pushed forward and aft by hand it became apparent that the filler was not properly bonded and appeared to be covering a crack. The filler could be easily pried off with a screwdriver, revealing a 4-inch-long crack at the weld that joined the sump to the mounting flange. The crack had propagated beyond the filler contact area (see Figure 1). The area of the sump where the filler had been installed showed evidence of abrasive marks consistent with bonding preparation, but most of the paint remained.

Figure 1 - Oil sump flange The pilot, who was a Federal Aviation Administration-certified airframe and powerplant mechanic with inspection authorization, later confirmed that a crack had been there since December 2023, but the leak was a nuisance and not significant, with a total oil consumption of about 1 quart every 4-6 hours. He decided to repair the crack with “Steelstik” epoxy putty, manufactured by J-B Weld. After the repair he performed multiple engine ground test runs. The accident was the first flight since he had made the repair.

Review of the data stored on the airplane’s engine monitor revealed a gradual loss of oil pressure as described by the pilot.