Accident Overview
On June 29, 2010, about 1745 Alaska daylight time, a float-equipped Cessna U206G airplane, registration N4596U, sustained substantial damage to its wings, rudder, and fuselage during an emergency off-airport landing approximately 16 miles west-southwest of Iliamna, Alaska. The airplane was operated by Rust's Flying Service, Anchorage, Alaska, as a visual flight rules (VFR) revenue sightseeing flight under 14 Code of Federal Regulations, Part 135. The commercial pilot and four passengers were not injured; the remaining passenger received minor injuries. The flight was returning to the operator's base at the Lake Hood Seaplane Base, Anchorage, and company flight following procedures were in effect.
Pilot's Account
During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), a representative for the operator stated that the pilot reported a complete loss of engine power, which precipitated an emergency descent and off-airport landing. The pilot reportedly observed a rise in exhaust gas temperature (EGT) before the loss of power. The float-equipped airplane landed on tundra-covered ground and nosed over. The pilot reported adding 42 gallons of aviation fuel prior to the return flight to Anchorage.
In a written statement to the FAA dated July 1, the pilot wrote that about 40 minutes into the flight, he saw the EGT rise above normal cruise temperature. He enriched the mixture from 15 gallons per hour (GPH) to 18 GPH to cool the engine. Shortly thereafter, the engine quit completely. After several failed attempts to restart the engine, he focused on landing the airplane.
Examination Findings
On August 18, the airplane was examined by the NTSB IIC at an airplane maintenance facility in Wasilla, Alaska. During an attempt to rotate the propeller, it was discovered that the propeller would not rotate, and the rear accessory portion of the engine did not appear to be connected through the crankshaft to the propeller.
On November 9, the airplane's engine was disassembled at an airplane maintenance facility in Palmer, Alaska, with representatives from the FAA and the engine manufacturer in attendance. During disassembly, it was discovered that the engine's crankshaft had fractured and separated at the number 2 journal.
The crankshaft was shipped to the NTSB material laboratory in Washington, D.C., for examination. The laboratory engineer found "ladder cracking," indicative of oil starvation, associated with the journal fracture. The NTSB material laboratory report is contained in the public docket for this report.
Engine History
Prior to October 21, 2008, the accident airplane's engine, serial number 286450-R, was overhauled by Aero Recip in Anchorage, Alaska. The overhauled engine was sold to Mulchatna Air in Dillingham, Alaska, and installed in one of their airplanes. During the first flight, the engine lost oil pressure; the pilot landed, and the engine oil filter was checked for metal particles. Finding metal in the filter, the owner requested the engine be replaced by Aero Recip, which it was. During a telephone conversation with the NTSB IIC, the owner of Mulchatna Air said that a couple days after returning the engine, he received a telephone call from Aero Recip stating they could not find anything wrong with the engine and were returning it to service.
According to the engine's log book, on June 24, 2009, the engine was removed from the airplane due to possible metal contamination. The engine was partially disassembled by Aero Recip and inspected. No contamination was found, so the engine was reassembled and test run three times. After each run, the oil filter was examined, with no notable contaminants or ferrous metal found. Aero Recip returned the engine to service.
On July 7, 2009, the engine was installed in the accident airplane. At the time of the accident, the engine had 441 hours of operation since the October 21, 2008 major overhaul.