CEN16FA210

A loss of engine power during cruise flight for reasons that could not be determined because a test run of the engine did not reveal any mechanical malfunctions or anomalies that would have precluded normal operation. Contributing to the accident were the tree stumps at the forced landing site.

The passenger reported that, about 15 minutes after takeoff on the cross-country flight, the engine began "stalling in and out." Although the pilot attempted to troubleshoot the issue, he could not remedy it, and selected a dirt road as a forced landing site. The passenger stated that the airplane was too fast and too high to land, and the pilot circled the airplane for a second approach. About 150 feet above the ground, the engine experienced a total loss of power. The airplane touched down in an area of tree stumps and immediately nosed over. Toxicology testing of the pilot revealed the presence of diphenhydramine; however, the level detected was too low to quantify and was unlikely to be impairing. No shoulder harnesses were installed, and their installation was not required. Advisory Circular 91-65, in part, stated, "The [National Transportation Safety Board] concluded that shoulder harness use is the most effective way of reducing fatalities and serious injuries in general aviation accidents." Although the spark plugs displayed significant wear, a test run of the engine revealed no anomalies that would have precluded normal operation. A carburetor icing probability chart showed the airplane was operating in conditions conducive to serious icing at glide power; however, the airplane should not have been susceptible to carburetor icing at the cruise power setting at which it was operating. The investigation could not determine a reason for the loss of engine power.

Soot colored discoloration consistent with a ground fire was observed on the carburetor and on the firewall mounted fuel strainer. The airplane did not have shoulder harnesses installed and was not required to have them installed at the time it was certified. A hammer and surveying equipment were found unsecured in the rear section of the cabin. The accident engine, propeller, and vented fuel cap were sent to the engine's manufacturer in Mobile, Alabama. The engine had damaged items to include damaged spark plug wires, exhaust pipes, intake pipes, and engine mounts. Drained engine oil was strained and no debris was observed in the strainer. The disassembled carburetor showed that there was sooting inside of the venturi area and on the upstream side of the throttle. The disassembled fuel bowl revealed no anomalies other than the liberated floats. The bowl vent strainer screen housing and its screen were deformed and replaced with exemplar items. The accelerator pump's plunger was damaged during the on scene examination and was replaced with an exemplar plunger. The fuel line inlet connection to the carburetor was damaged and replaced. The inlet screen did not contain any debris. The float and lever assembly was replaced with an exemplar assembly. The carburetor was reassembled and mounted to the engine along with exemplar spark plug wires, exhaust pipes, intake pipes, and engine mounts. The engine was mounted on a test stand and taken to a test cell for an engine run. The engine was operational during the engine run. The vented fuel cap was visually and operationally inspected. The exterior portion of the cap was discolored consistent with exposure to sunlight and weather. The venting passage was found to be blocked and further inspection showed that there was debris in its internal cavities. The airplane operator reported that he came across an article in the Cessna Pilots Association (CPA) magazine about vapor lock in the 172 series Cessna airplanes. The CPA article is appended to the docket material associated with this case. Party members were asked to see if vapor lock applied to this Cessna 175 investigation. The airplane and engine manufacturers' safety representative indicated that there is no history of a design issue or any issue in reference to vapor lock. Advisory Circular 91-65, Use of Shoulder Harness in Passenger Seats, in part, stated: The [National Transportation Safety Board] found that 20 percent of the fatally injured occupants in these accidents could have survived with shoulder harnesses (assuming the seat belt fastened) and 88 percent of the seriously injured could have had significantly less severe injuries with the use of shoulder harnesses. Energy absorbing seats could have benefited 34 percent of the seriously injuries. The safety board concluded that shoulder harness use is the most effective way of reducing fatalities and serious injuries in general aviation accidents. At 1653, the recorded weather at the Grider Field Airport, near Pine Bluff, Arkansas, was: Wind 110 degrees at 6 knots; visibility 10 statute miles; sky condition clear; temperature 31 degrees C; dew point 19 degrees C; altimeter 29.95 inches of mercury. The temperature and dew point were plotted on a carburetor icing probability chart. The intersection of the temperature and dew point was within the serious icing-glide power envelope. An autopsy was performed on the pilot and toxicological samples were taken by the Arkansas State Crime Laboratory. The pilot's cause of death was listed as scattered superficial blunt force injuries. The FAA Civil Aerospace Medical Institute (CAMI) prepared a Final Forensic Toxicology Accident Report on the samples taken. The report indicated: Diphenhydramine detected in Urine Diphenhydramine detected in Blood (Cavity) The CAMI description of Diphenhydramine indicated that it "is a common over the counter antihistamine used in the treatment of the common cold and hay fever." The 66-year-old pilot held a Federal Aviation Administration (FAA) private pilot certificate with an airplane single engine land rating. He also held a FAA third-class medical certificate that was issued on February 26, 2016, with a limitation that he must wear corrective lenses. Copies of pilot logbook excerpts obtained by the FAA did not have the pilot's recorded flight experience totalized. However, the pilot reported on his application for his medical certificate that he accumulated 147 hours of total flight time with 0 hours in the six months preceding his medical. The medical indicated the pilot was 76 inches tall. An endorsement in the pilot logbook excerpts showed that the pilot completed a flight review on April 21, 2016. N6649E, a Cessna 175, Skylark, serial number 56149, was an externally braced high-wing, propeller-driven, fixed landing gear, semi-monocoque design, four-seat airplane. A 175-horsepower, geared, six-cylinder, air cooled, horizontally opposed, carbureted, Continental GO-300-A engine, marked with serial number 6208-9-A, powered the airplane. The propeller was a two-bladed, all-metal, fixed pitch, McCauley model 1B175/MFC8460, with serial number 70765. Copies of airplane logbook excerpts obtained by the FAA showed that an annual inspection was completed on October 6, 2015. An endorsement in the logbooks indicated the airplane had accumulated 2,247.2 hours of total time and the tachometer indicated 0.0 hours at the date of the annual inspection. Fueling records indicated the airplane was serviced with 17.0 gallons of 100 low lead aviation fuel at MEZ on June 6, 2016, and was topped off with 14.5 gallons of 100 low lead aviation fuel at MEZ on June 7, 2016. The airplane was found inverted about 24 miles and 305 degrees from 55M in an open area of rolling land with clear-cut tree stumps present. The first found witness mark was a ground scar consistent with a width of a landing gear tire, which was observed next to a tree stump that had an indented witness mark. The inverted wreckage was found about 40 feet and 120 degrees from that stump. A ground scar depression consistent with the shape of the cowling was observed about 20 feet from that stump in the same direction to the wreckage. A FAA inspector found the fuel selector handle in the BOTH tank position shortly after arriving at the accident site and moved it to the OFF position. A picture of the fuel selector revealed its securing cotter pin was partially engaged. A subsequent on-scene examination of the wreckage was conducted. Flight control cables were traced from the cockpit controls to their respective flight control surfaces and flight control cable continuity was established. The wing flaps were found in the 10-degree extended position and flap control cable continuity was established. Measurement of the elevator trim actuator extension was 1.25 inches, which was consistent with a neutral elevator trim tab position. Engine controls were moved in the cockpit and engine cable continuity was established when their opposite ends moved respectively. The carburetor was found separated from its engine mounting surface. The propeller remained attached to the engine's propeller flange and the propeller did not exhibit any leading edge nicks. The vacuum pump separated from its mounting pad. The fuel line to the carburetor was separated at its carburetor inlet fitting. The carburetor, below the fuel inlet fitting area, was discolored consistent with the color of sooting. The carburetor was disassembled and its floats were found loose in the float chamber, where the float's attaching solder had a shiny appearance consistent with being melted. The firewall fuel strainer was deformed and discolored consistent with the color of sooting. The strainer's screen was found unobstructed and its glass bowl was found broken. The tachometer indicated 28.12 hours. The fuel tank selector valve was removed and it operated normally in all its positions. Bo