History of Flight
On April 6, 2013, about 1035 Pacific daylight time, a Beechcraft A36TC airplane, N36SG, was substantially damaged during a forced landing in Big Bear Lake, Big Bear City, California. The pilot received serious injuries, and three passengers sustained minor injuries. The flight was conducted under Part 91 of the Federal Aviation Regulations with visual meteorological conditions at the accident site. The airplane had departed McClellan-Palomar Airport (CRQ) in Carlsbad, California, on an instrument flight rules (IFR) flight plan, destined for Big Bear City Airport (L35).
En route, the pilot canceled the IFR plan and continued with flight following services from SoCal Approach. After passing ARRAN intersection, at an estimated altitude between 9,500 and 9,000 feet, the airplane experienced a sudden high-frequency vibration. The pilot reduced power and notified the controller. The manifold pressure gauge gave erratic indications. The airplane descended more rapidly than desired, and the pilot adjusted engine controls to normal cruise values but did not get a commensurate response. While abeam a visual landmark at about 6,900 feet, the pilot switched to the airport advisory frequency. He observed a causeway and turned right to avoid it, then broadcast that he could not make the airport and would land in a field west of the airport. During a right bank, the right wingtip contacted the lake, and the airplane came to rest inverted in water about 2 feet deep, about 1.25 miles southwest of runway 8 threshold at L35.
An eyewitness on the lakeshore heard the airplane, saw it about 30 feet above the lake heading south, then saw it bank right and impact. He called 911 and ran into the lake to help.
Pilot and Aircraft Information
The pilot held a private pilot certificate with airplane single-engine land and instrument ratings, with about 1,300 total flight hours, including about 1,250 in the accident make and model. His most recent flight review and third-class medical were completed in April 2012.
The airplane was manufactured in 1979, equipped with a Teledyne Continental TSIO-520 series engine and a McCauley model 3A32C76 propeller. The registration changed from N66656 to N36ML in 1986, then to N36SG in 1996. The pilot purchased it in November 1998. Maintenance records showed multiple avionics upgrades and aftermarket wing tip tanks. The accident engine and propeller hub had different serial numbers than originally installed; all three propeller blades were original.
Meteorological Conditions
The 1035 weather observation at L35 included winds from 260 degrees at 8 knots, visibility 10 miles, clear skies, temperature 15°C, dew point -8°C, and an altimeter setting of 30.14 inches of mercury.
Wreckage and Impact
The airplane came to rest inverted in about 2 feet of water, about 100 feet from shore. The left wing separated and was found about 75 feet away. The cabin remained largely intact. The pilot and passengers exited through the cabin doors. Recovery efforts caused some additional deformation. Examination of the engine and airframe found no pre-impact anomalies that would have precluded normal operation.
The propeller remained attached but all three blades were free to rotate independently in the hub, with aft bending and twisting deformation. The propeller flange had no cracks. The JPI EDM-700 engine monitor and Shadin 1530 fuel flow monitor were downloaded; no engine or fuel anomalies were found.
Propeller Examination
Disassembly revealed multiple fractured components, sandy material, and sludgy oil. The hub serial number indicated a 1991 date; the blades were manufactured before 1970. The propeller had been modified from grease-filled to oil-filled and had prior dynamic balance marks.
Three actuating pins were found loose in the hub. One had fractured due to fatigue, originating at a thread root. The other two were bent and stripped from their ferrules. Hardness values were lower than current specifications, consistent with superseded pins. The three ferrules remained attached to blades. The ferrule with the fractured pin had two blind holes; the others had one each. The fractured pin contacted the bottom of its blind hole. Aft surfaces of ferrules showed bulging below the blind holes.
Propeller history showed overhauls in 1992 and 1998. The 1998 overhaul complied with service bulletins through SB218. Parts lists from 1998 did not detail whether actuating pins were replaced. The propeller exceeded the 60-month overhaul calendar limit by about three times (15.2 years since overhaul) but remained within the 1,500-hour service limit (1,361 hours since overhaul).
Communications
Communications were normal until about 1033, when the pilot reported a serious vibration but intended to continue to L35. The controller asked about the cause; the pilot described instrument indications. The controller asked if he could maintain altitude; the pilot believed he could. The controller advised holding altitude and circling down over the airport. The pilot concurred. No further communications were recorded.