On August 2, 2024, about 0824 Alaska daylight time, a float-equipped De Havilland DHC-2 airplane, N4444Z, sustained substantial damage when it was involved in an accident near Anchorage, Alaska. The pilot and six passengers were uninjured. The airplane was operated as a Title 14 Code of Federal Regulations Part 135 non-scheduled flight. The pilot reported that, shortly after takeoff, as the airplane climbed to about 200 ft above the water, the engine started to sputter, run rough, and began to lose power. Video footage shows a puff of white smoke coming from the left side of airplane’s engine compartment just before the airplane began to lose altitude. The pilot was able to execute a left turn and make an emergency landing on the remaining portion of the lake. Shortly after touchdown, the airplane’s floats collided with the shoreline, the left wing impacted a tree, and the airplane came to rest in an area of brush which resulted in substantial damage to the left wing and fuselage. After the accident, the operator erroneously thought the airplane had been released to them and without federal oversight, the operator conducted the following inspections: checked fuel for contaminants, removed and inspected all spark plugs, checked the timing on the magnetos, completed compression checks on all cylinders, inspected all the intake and exhaust valves with a borescope, checked valve clearances, inspected rocker arms and rocker shaft nuts and reported that everything was found to be within normal limits. After accomplishing all the above inspections, the operator ran the engine. The engine was removed, crated, and sent to Tulsa Aircraft Engines in Tulsa, Oklahoma, for examination under NTSB oversight. Compression on all cylinders was found to be within normal limits. The timing on both magnetos was found to be within limits. Cylinder No. 3 was replaced three days before the accident and was included with the engine. Cylinder No. 3 was disassembled, and the valve guide clearances were found to be within limits. All remaining cylinders were disassembled. Although the No. 2 cylinder valve guide clearances were tightened beyond normal limits, the clearance on all other cylinders were within normal limits. Valve gap clearances on all cylinders were found to be within limits. All nine cylinders were removed; all valves were smooth and operated with full travel. All pushrods were straight, and the pressed ends were firmly attached. All pistons and piston pins were inspected and found to be in serviceable condition. The engine nose case was removed, exposing the camshaft ring and gears. A visual inspection of crankshaft, master rod, articulating rods, and accessory section showed no anomalies. The engine case was found to be in serviceable condition. A dial indicator was installed to check the camshaft ring runout and camshaft lobe lift. The camshaft ring was found to be within serviceable limits and continuity was confirmed with the crankshaft. The camshaft roller tappets were found to be in serviceable condition. The carburetor was disassembled and the accelerator pump and float moved normally. Fine metal and non-metal particles were found in the carburetor bowl. The carburetor fuel screen was found to have minor debris that appeared to be silicone sealant. Small non-metal particles were observed past the carburetor screen in the economizer. The impeller was intact and rotated smoothly. The fuel pump drive gears turned in sync with the magneto drive gears and impeller when the crankshaft was rotated. The engine did not exhibit any indications that the lubrication system was not functioning properly at the time of the accident. No thermal damage or heat signatures were found. The oil screen was removed and found to be clean. No engine anomalies were found that would have prevented normal operation.