Accident Overview
On December 29, 2021, at 1622 eastern standard time, a Cessna 207 airplane, registered N1596U, sustained minor damage during an accident in the Florida Bay near Marathon, Florida. The pilot received serious injuries, and both passengers sustained minor injuries. The flight was operated by ExecAir of Naples under 14 CFR Part 135 as an on-demand air carrier.
Flight Description
The flight originated from Naples Municipal Airport, Florida, to Marathon, Florida, and the accident occurred on the return leg. Preflight, engine start, takeoff, and initial climb were uneventful. After reaching about 3,800 feet msl, the airplane began shaking and losing power. The pilot observed normal engine instrument readings and oil pressure, but power was not restored despite adjusting controls. She established best glide, transmitted a mayday call, and turned back toward Marathon. During descent, oil was observed leaking from the engine cowling. Realizing the aircraft could not reach land, she performed a forced ditching. The airplane remained upright in open water, and occupants egressed. A passing recreational vessel rescued them shortly after.
Post-Accident Examination
After recovery from the water, NTSB examination revealed a large fracture hole in the top aft portion of the engine case near the No. 2 cylinder. Saltwater corrosion consistent with submersion was present. Borescope inspection of all six cylinders showed no other visible damage to valves or pistons. The No. 2 connecting rod crankshaft end was heavily fragmented, with pieces in the oil pan. The crankshaft journal for the No. 2 connecting rod showed wear marks, heat transfer, and deformation of the oil transfer hole. A small debris fragment consistent with bearing material was found in the oil transfer hole. Other oil transfer holes appeared normal.
Forensic Examination
Materials laboratory examination of the No. 2 connecting rod assembly and bearings from Nos. 1, 2, and 3 connecting rods found the No. 2 rod end tinted black from high heat, with its bearing thinned, fractured, and deformed. The No. 3 bearing halves were darkened with displaced babbitt. The No. 1 bearing appeared normal. The No. 2 connecting rod and its bolts exhibited features consistent with fatigue.
Maintenance History
Total airframe time was 13,496 hours; engine time since new was 3,728 hours; time since major overhaul was 861 hours. The engine was overhauled on December 10, 2014, and installed on January 20, 2016. On November 23, 2021 (7.1 hours before accident), Nos. 2 and 6 cylinders were replaced due to excessive ring blow-by and a fractured exhaust stud. Oil was changed, and left exhaust collector replaced. On December 23, 2021 (2.2 hours before accident), an overhauled propeller and propeller governor were reinstalled. The mechanic reported no oil contamination in recent work, except excessive carbon, and no recent oil analysis was performed.