WPR13FA086

An in-flight encounter with icing conditions during descent, which resulted in the airplane exceeding its critical angle-of-attack and experiencing an aerodynamic stall followed by an in-flight breakup.

During a visual flight rules cross-country flight, air traffic control was providing flight-following services. The pilot informed the controller that there was cloud cover ahead and requested an instrument flight rules clearance and approach to the destination airport. The controller granted the clearance and then instructed the pilot to maintain 14,000 ft; the pilot read back the clearance. The pilot then requested a lower altitude and was advised to expect a lower altitude in 10 to 12 miles. The pilot was subsequently cleared for a descent to 7,000 ft and issued arrival instructions. Two minutes later, the controller advised the accident pilot of a pilot report of icing in the area. One minute later, the controller issued a clearance to 6,000 ft but received no response from the pilot. The controller issued the clearance again, and the pilot acknowledged the instruction. The controller relayed a nearby outside air temperature but received no response from the pilot. The controller made several attempts to contact the pilot and also asked another pilot to try to establish contact; all attempts were unsuccessful. Two minutes later, radar contact was lost. The wreckage was located about 1 mile from the last radar return and was distributed over the terrain for about 1/2 mile, indicating that an in-flight breakup had occurred. A postaccident examination of the airframe or engine revealed no anomalies that would have precluded normal operation. A weather study indicated that the airplane likely encountered light-to-moderate precipitation, especially near the end of the radar flight track. Precipitation and clouds would have reduced visibility. Considering the environmental freezing level, the airplane likely encountered supercooled liquid water and snowflakes about the time that voice communication was lost. Pilot reports in the immediate area described increasing instrument meteorological conditions (IMC) along with light-to-moderate icing conditions. The reports described the flight conditions as mostly smooth with some light turbulence when passing in and out of cloud tops. Along with the likely IMC, the airplane likely experienced moderate or greater icing conditions around the accident time. The airplane likely developed ice on the wings, which resulted in an aerodynamic stall followed by a loss of control and in-flight breakup during the descent.

The pilot was in contact with Bakersfield Approach Control on frequency 118.9. The NTSB IIC, the FAA, Beech, and CMI examined the wreckage at Aircraft Recovery Service, Littlerock, California, on March 15, 2013. A full report is contained within the public docket for this accident. Airframe There were multiple disconnects in the flight control system. All identified flight control cables were splayed. All fractured and separated components had angular and jagged fracture surfaces. The left wing sustained more damage than the right wing. It fragmented into two pieces, and both pieces exhibited spanwise creases. The wing separated midspan along a jagged fracture surface. The spar at the separation point remained permanently deformed about 30 degrees in an upward direction. The aileron separated into three sections. The inboard aileron tore along a jagged angular plane at the inboard hinge; the rod end separated at the hinge. The inboard portion of the aileron's middle section also remained permanently deformed in an upward direction. The outboard hinge, and the aileron section outboard of it, remained attached to the wing. The flap remained attached to the inboard half of the left wing. The right wing separated at the wing root. There were chevron wrinkles from the front leading edge at the tip aft to the trailing edge. The chevrons were more pronounced on the aft outboard third of the wing; this section exhibited permanent trailing edge up deformation. The right side of the tail section sustained more damage than the left side. The inboard leading edge of the right horizontal stabilizer was bent down; the inboard trailing edge of the right horizontal stabilizer was bent up. There was a deep chevron from inboard mid-chord to trailing edge midspan. The right ruddervator fragmented into four pieces. The inboard piece contained the hinge; the second piece contained the entire trim tab. The third piece consisted of the outboard section of the ruddervator. The fracture surfaces were angular and jagged. The right counterweight separated at the tip, the fracture surface was angular and jagged. The left horizontal stabilizer exhibited a shallow chevron from inboard mid-chord to the trailing edge quarter-span. The left ruddervator remained connected in place; the counterweight separated at the tip along a jagged and angular fracture surface. The left trim tab remained connected in place with the control cables connected at the control surface. The ruddervator trim measured 1.25 inches, which equated to a position outside the permissible range. The fuel selector valve was in an intermediate position. Engine Recovery personnel had removed the cowling, and slung the engine from a hoist. All cylinders sustained crush damage to the top cooling fins; the left (even) side cylinders sustained the most distortion. Removal of the top spark plugs revealed that all center electrodes were the fine wire type. The number six spark plug (front left cylinder) had fragmented. The spark plug electrodes were gray, which corresponded to normal operation according to the Champion Aviation Check-A-Plug AV-27 Chart. A borescope inspection revealed no mechanical deformation on the valves, cylinder walls, or internal cylinder head. There was some debris in cylinder number six (the spark plug had been breached). The crankshaft rotated with resistance when manually rotated with the propeller. The top of the engine sustained crush damage, and the magneto drives were impinging on the case. Removing the magneto drives and moving the fractured case metal freed the crankshaft, and allowed the engine to turn through 360 degrees, but with some difficulty. Several push rods were bent. The valves moved approximately the same amount of lift in firing order, except for the intake valve on cylinder number six. After striking the valve with a hammer, it became free and moved. Thumb compression was obtained on all cylinders except cylinder number six. The gears in the accessory case turned freely. Both magnetos fragmented, and could not be tested. The oil sump screen was clean and open. The governor screen was clean. Disassembling the oil filter revealed that the filter element was free of debris. The engine driven fuel pump drive gear was not recovered. The rubber diaphragm in the fuel distribution valve was torn through 180 degrees of its circumference, the screen was clean, and there was no observable contamination. The fuel nozzles were open, and the screens were clean. Propeller blade one was the least damaged. Propeller blade two separated about 6 inches from the hub, and was bent aft. The fracture surface was a grainy, matt surface, and angular. From the inboard fracture surface, the blade curled aft about 45 degrees for 9 inches, forward 30 degrees for the next 10 inches, and then gradually aft 5 degrees for 9 inches. The forward surface of the outboard half of the blade had spanwise striations. The outer 2 inches of propeller blade three's tip curled aft 45 degrees. At the conclusion of the postaccident airframe and engine examinations, no evidence of mechanical anomalies was revealed that would have precluded normal operation. The Kern County Sheriff/Coroner completed an autopsy, and determined that the cause of death was multiple blunt force trauma. The FAA Forensic Toxicology Research Team, Oklahoma City, Oklahoma, performed toxicological testing of specimens of the pilot. They did not perform tests for carbon monoxide or cyanide. The report contained the following findings for tested drugs: Losartan detected in muscle and liver; Metropolol detected in detected in muscle and liver. The report contained the following findings for volatile: 10 (mg/dL, mg/hg) ethanol detected in muscle; no ethanol detected in the brain. The report stated that the ethanol found in this case was from sources other than ingestion. The National Transportation Safety Board's (NTSB) Meteorologist was not on scene for this investigation and gathered all the weather data for this investigation from the NTSB's Washington D.C. office and from official National Oceanic and Atmospheric Administration (NOAA) National Weather Service (NWS) sources including the National Climatic Data Center (NCDC). The meteorologist prepared a Weather Study report, which is in the public docket for this accident. Pertinent parts of the report follow. The NWS Surface Analysis Chart for 1600 PST indicated that the accident site was located in a region where clouds and precipitation would be expected. The NWS Storm Prediction Center (SPC) Constant Pressure Charts for 1600 PST indicated that the accident site was located in a very favorable location for vertical motion, clouds, and precipitation given the low, mid, and upper-level environment. No thunderstorm products or convective outlooks were valid for the accident site at the accident time. Surface observations for the area surrounding the accident site was documented utilizing official NWS Meteorological Aerodrome Reports (METARs) and Specials (SPECIs). Meadows Field Airport (KBFL) was the closest official weather station to the accident site; it was located 3 miles northwest of Bakersfield, California, and had an Automated Surface Observing System (ASOS) whose reports were supplemented by the air traffic control (ATC) tower. KBFL was located 18 miles south-southwest of the accident site, at an elevation of 510 feet, and had a 14 degree easterly magnetic variation. KBFL weather at 1554 PST was wind from 330 degrees at 6 knots, 10 miles visibility and light rain, an overcast ceiling at 3,600 feet agl, temperature of 10 degrees C, dew point temperature of 6 degrees C, and an altimeter setting of 30.08 inches of mercury. The remarks section noted that it was an automated station with precipitation discriminator, and rain began at 1538 PST. Porterville Municipal Airport (KPTV) was located 3 miles sou