Accident Summary
On August 2, 2024, at approximately 0824 Alaska daylight time, a De Havilland DHC-2 floatplane, registration N4444Z, sustained substantial damage during an accident near Anchorage, Alaska. The aircraft was operating under Title 14 Code of Federal Regulations Part 135 as a non-scheduled flight with a pilot and six passengers aboard; none were injured.
The pilot reported that shortly after takeoff, while climbing to about 200 ft above the water, the engine began to sputter, run roughly, and lose power. Video footage captured a puff of white smoke emanating from the left side of the engine compartment just before the airplane started descending. The pilot executed a left turn and performed an emergency landing on the remaining portion of the lake. Immediately after touchdown, the floats struck the shoreline, the left wing hit a tree, and the airplane came to rest in brush, resulting in substantial damage to the left wing and fuselage.
Post-Accident Inspections
Following the accident, the operator mistakenly believed the aircraft had been released to them and conducted inspections without federal oversight. These checks included fuel contamination testing, spark plug removal and inspection, magneto timing verification, cylinder compression checks, borescope inspection of intake and exhaust valves, valve clearance measurement, and inspection of rocker arms and rocker shaft nuts. All findings were reported to be within normal limits. The operator then ran the engine.
Engine Examination
The engine was subsequently removed, crated, and sent to Tulsa Aircraft Engines in Tulsa, Oklahoma, for examination under NTSB oversight. Compression on all cylinders was found normal. Both magnetos were timed within limits. Cylinder No. 3, which had been replaced three days prior to the accident, was disassembled; its valve guide clearances were within limits. All remaining cylinders were disassembled. While No. 2 cylinder's valve guide clearances were tighter than normal, the others met specifications. Valve gap clearances on all cylinders were acceptable. All nine cylinders were removed; valves moved smoothly with full travel, pushrods were straight and securely attached.
Pistons and pins were serviceable. The nose case was removed, revealing the camshaft ring and gears; visual inspection of the crankshaft, master rod, articulating rods, and accessory section showed no anomalies. The engine case was serviceable. A dial indicator check of camshaft ring runout and lobe lift found the ring within limits, with continuity to the crankshaft. Camshaft roller tappets were serviceable.
The carburetor was disassembled; the accelerator pump and float moved normally. Fine metal and non-metal particles were found in the bowl, and the fuel screen contained minor debris resembling silicone sealant. Small non-metal particles were observed past the screen in the economizer. The impeller was intact and rotated smoothly; fuel pump drive gears turned in sync with magneto drive gears and impeller when the crankshaft was rotated.
No evidence suggested the lubrication system malfunctioned at the time of the accident. No thermal damage or heat signatures were found; the oil screen was clean.
No engine anomalies were identified that would have prevented normal operation.