CEN21LA265

The airplane was in cruise flight at 1,000 ft above ground level when the engine sputtered. As the pilot executed a 180° turn toward the airport, the engine lost all power. The pilot also reported that the radios lost power. The airplane impacted trees in a heavily wooded area short of the open field and sustained substantial damage to the wings and empennage during the forced landing. The airplane had undergone numerous modifications, including a change from bladder fuel tanks to integral fuel tanks in the wings. Four days before the accident, a mechanic had drained the left wing of fuel and resealed it with a sealant. The wing was then refueled, and leak checked. Postaccident examination showed sealant contamination in the left fuel tank, varying in size up to 1 inch. The sealant was not adhering to the inside of the wing tank. Although the fuel screens were found unobstructed, due to the size and number of the sealant pieces fuel flow from the left tank could likely have been obstructed, resulting in a loss of engine power.

On June 14, 2021, at 0852 eastern daylight time, a Cessna 180K, N13159, was substantially damaged when it was involved in an accident near Columbus, Ohio. The pilot sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that she took off uneventfully and executed a climbing right turn before leveling off at 1,000 ft above ground level. Shortly thereafter, the airplane’s engine sputtered briefly. The pilot contacted air traffic control and initiated a 180° turn toward the airport when the engine lost all power. Unable to make it to the airport, the pilot initiated a slight left turn towards an open field; she also noted that airplane’s radios lost power. The airplane struck trees in a heavily wooded area short of the open field before impacting terrain. The airplane sustained substantial damage to the wings and empennage. The airplane and engine were examined. The airplane had been modified from a carbureted to a fuel injected engine and the wings had been changed from bladder fuel tanks to integral fuel tanks. Examination of the right wing showed that the fuel tank was intact, and no anomalies were noted inside of the tank. The fuel cap was not in place; however, no fuel staining was evident. Examination of the left wing identified fragments of off-white sealant found loose within the fuel tank, varying in size up to about 1 inch and consistent with Chem Seal 3204. The sealant appeared to have been applied to the vertical and lower skin structure of the fuel tank, exhibiting cracking and flaking. The middle and outboard wing drains had a grey color sealant observed over the off-white sealant. About 12 pieces of grey sealant were also observed loose in the fuel tank. The fuel cap was in place. The finger screens in both tanks were clear of debris. The fuel strainer was removed and contained fuel. No water was observed. Within the fuel strainer screen a minor dark substance was observed, but the screen was otherwise clear. Air was blown through the fuel lines at both wing roots and fuel was expelled through the fuel strainer. The fuel selector valve was manipulated and functioned normally. Examination of the engine showed no visual signs of catastrophic failure. Further examination of the engine’s fuel components identified a minor blockage in the No. 2 nozzle and a white powder on the surface of the fuel distributor spring on its larger side. The fuel control unit was removed and displayed minor leaking at the fuel metering unit. The electrical system was not tested. Review of the airplane’s maintenance logbooks showed that on June 10, 2021, four days before the accident, the airplane’s left fuel tank was drained and resealed with Chem Seal CS3204B2. The entry noted that tank was refilled with 100LL and leak checked. The mechanic was not interviewed. According to Chem Seal documentation, the surface area for Chem Seal application must be free of contaminants andthe sealant has a specific mixing and cure schedule. The NTSB Materials Laboratory examined the residue from a fuel distribution spring as well as sealant fragments. When examined by a Fourier Transform Infrared spectrometer, the residue from the spring was not consistent with the sample of the sealant. The analysis was not able to identify the residue and its source could not be determined.