WPR24LA314

While the airplane was en route to a local airport, the engine suddenly lost power and the airplane began to shake. The pilot noted rapidly decreasing cylinder head temperature readings on most cylinders and the loss of the temperature reading for the No. 4 cylinder. He turned the airplane toward the nearest airport, and the engine then lost all power. The pilot realized that the airplane would not glide to the nearest airport and selected a field to land in. He initiated an emergency landing to the field and the airplane nosed over, coming to rest inverted. Postaccident examination of the engine revealed that the No. 4 fuel injection assembly tube was not contained in its retention clamp, and the elastomer sleeve that cushions the clamped tube was displaced from its normal position. Examination of the tube during disassembly revealed a fracture where it intersected the shank of the ferrule that had been brazed onto the inboard end of the tube. Further examination of the fracture at the NTSB laboratory revealed that the fracture surfaces were consistent with fatigue and that the elastomer sleeve displayed wear marks consistent with previous clamping. The engine’s fuel flow divider was tested with the five intact fuel injection assembly tubes from the accident engine and one surrogate tube for the No. 4 position. The flow test failed when the No. 4 tube was removed to simulate the fracture. The investigation could not determine how long the No. 4 fuel injection assembly tube had been displaced from the retention clamp before the tube’s in-flight failure and subsequent engine failure.

Review 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. On 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. Postaccident 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.