On March 5, 2024, about 1704 Pacific standard time, a Cirrus SR-22T, N927CS, sustained minor damage when it was involved in an incident near Bellevue, Washington. The flight instructor and the pilot receiving instruction were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight.
The flight instructor and pilot receiving instruction reported that after takeoff from runway 34, Renton Municipal Airport, they leveled off at about 2,500 ft mean sea level (msl). A few minutes later, the engine rpm surged a few times, followed by the sound of a loud bang and subsequent total loss of engine power. Unable to restart the engine, they deployed the CAPS and the airplane descended under the parachute into a wooded wetland area adjacent to a residential neighborhood.
Figure 1: Front view of incident airplane. Examination of the incident site revealed that the airplane impacted terrain about 4 miles northeast of the departure end of runway 34. The airplane came to rest upright in an approximate 10° nose-low attitude on a heading of about 066° magnetic at an elevation of about 417 ft msl.
Review of the airframe and engine logbooks revealed that the engine, a Continental Motors TSIO-550-K1B, was overhauled in November 2019, and installed on the airframe in April of 2020. At the time of the incident, the engine had accumulated about 680 hours since major overhaul.
Examination of the recovered wreckage revealed damage to the nose landing gear fairing. Both wings and flaps were removed by recovery personnel. The engine remained attached to the fuselage via the engine mount. All six cylinders and all engine accessories remained attached. All fuel and oil lines appeared attached to their respective fittings. No evidence of any mechanical damage was observed to the engine crankcase. Throttle and mixture control continuity was established from the cockpit controls to the fuel servo and moved its available length when actuated by hand. The engine was shipped to the Continental Motors Inc. facilities for further examination.
Subsequent examination of the engine revealed that all six cylinders remained attached to the engine crankcase; no external visible damage was observed. The engine was placed on a rotating engine stand and disassembled. Fretting was observed on the parting surface of the No. 2 main bearing saddle. Damage to the Nos. 3 and 4-cylinders barrel skirts were observed. The No. 2 main bearing (M2) saddle remained in place and was deformed, consistent with a rotating main bearing. The engine was further dissembled to access the crankshaft and rotating mass. Damage to the interior crank case was observed throughout. The crankshaft near the M2 journal and the No. 3 connecting rod journal was fracture separated.
The crankshaft was sent to the NTSB Materials Laboratory, Washington, DC, for examination. The examination of the fracture surface revealed characteristics consistent with fatigue cracking that initiated at multiple locations along the radius of the web within the C3 journal. As this crack propagated rearward, a second smaller fatigue crack initiated along the radius of the aft M2 bearing. Review of maintenance records did not reveal any recent maintenance performed on the crankshaft.