CESSNA U206G

Full Narrative

HISTORY OF FLIGHTOn September 19, 2024, about 0819 Pacific daylight time, a Cessna U206G airplane, N6522Z, was substantially damaged when it was involved in an accident near West Sacramento, California. The pilot sustained minor injuries. The airplane was operated as a title 14 Code of Federal Regulations Part 91 other work use flight.
According to the pilot, he was enroute from Sacramento Mather Airport, (MHR), Sacramento, California, to Watts-Woodland Airport (O41), Woodland, California. The engine exhibited an abrupt decrease in power and began to shake violently. The pilot observed engine monitor alarms for rapid cooling and noted that the No. 4 cylinder head temperature reading was no longer being displayed on the engine data management display; all other cylinder temperatures were rapidly decreasing.
The pilot turned the airplane toward the nearest airport, Sacramento Executive Airport (SAC), and declared an emergency. Subsequently, the engine lost all power and the pilot determined that SAC was outside of the airplane’s glide range. The pilot initiated a forced landing to a field; during the landing roll the airplane nosed over, then came to rest inverted. AIRCRAFT INFORMATIONReview of maintenance records showed that the most recent annual inspection was completed on November 25, 2023. The most recent maintenance of any type was an oil change, completed on August 29, 2024. On July 6, 2022, the accident engine was installed on the accident airframe. AIRPORT INFORMATIONReview of maintenance records showed that the most recent annual inspection was completed on November 25, 2023. The most recent maintenance of any type was an oil change, completed on August 29, 2024. On July 6, 2022, the accident engine was installed on the accident airframe. WRECKAGE AND IMPACT INFORMATIONPostaccident examination of the airplane revealed substantial damage to both wings, the fuselage, the horizontal stabilizer, and the rudder. Examination of the engine at the manufacturer’s facilities revealed that the elastomer sleeve on the fuel injector assembly tube for cylinder No. 4 was displaced outboard of the tube’s retaining clamp, and the tube was unclamped. Disassembly of the fuel injector assembly tube revealed a fracture separation where it intersected the shank of the ferrule that was brazed onto the inboard end of the tube.
The fuel injector assembly tube and elastomer sleeve were examined by the NTSB materials laboratory. The fracture surfaces on the assembly tube were consistent with fatigue that originated at the lower forward quadrant of the tube’s outer diameter. A circumferential area of wear was observed on the elastomer sleeve.
The fuel manifold was flow-tested using the 5 intact fuel injection assembly tubes from the accident engine, and one surrogate tube for the No. 4 position. The first test was conducted with all 6 lines connected. The first test was normal until the 150 pounds per hour (pph) test point, when it failed due to high pressure. The second test was conducted with the No. 4 line removed and the line open. The second test failed due to low pressures at the 50, 100, and 150 pph test points.