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On January 28, 1996, approximately 1645 central standard time, a Cessna 152, N757UK, was destroyed during a forced landing following a loss of power near Conway, Arkansas. The private pilot and one passenger received serious injuries. The rental airplane, owned by a private owner, and operated by Barrett Aviation, Little Rock, Arkansas, was being flown under Title 14 CFR Part 91 when the accident occurred. The personal flight originated from Baxter County Municipal Airport, Mountain Home, Arkansas, at 1515, and was en route to North Little Rock, Arkansas. A VFR flight plan was filed; however, there is no record of the plan being activated. Visual meteorological conditions prevailed throughout the flight.
In an interview with the investigator-in-charge, the pilot reported that he had flown an uneventful flight from North Little Rock, Arkansas (departure time approx. 1100) to Mountain Home, Arkansas. He stated that the fuel tanks were "full" when he departed North Little Rock. Upon landing in Mountain Home, approximately 1215, the fuel tanks were "topped off" with an additional 11.1 gallons of 100 low lead aviation fuel. After visiting with family, he returned to the airport, performed a pre-flight, and then departed on a return flight to North Little Rock at 1515.
The pilot further stated that, after approximately 75 minutes of uneventful flying (altitude: approx. 3,500 feet AGL), the engine "appeared to backfire a couple times." He attempted to adjust throttle and the mixture control and activated the carburetor heat, "but the noise persisted." Subsequently, engine RPM began to "drop into the teens", and "any attempt to adjust the throttle and mixture control just resulted in worsening the engine operation." He added that, altitude and level flight could not be maintained and he located a field to execute a forced landing. The pilot "circled the field a couple of times" to set up for the final landing. He recalled that, during the emergency descent, the winds were "gusting up to 40 miles per hour, and thus created additional difficulties." He recalled that, during the last descending turn, the airplane "just missed some tree tops" and then the "plane's nose [was] diving quickly toward the ground." As the nose dropped, he heard the stall warning horn for about 1 second and then it "abated as speed increased."
Six eye witnesses were interviewed and provided statements to the investigator-in-charge. According to two of the witnesses (closest to the accident site), the engine "sounded like it was cutting out", then they observed the airplane circling and descend into a field "nose first." Two other witnesses, who were driving in a car adjacent to the accident site, observed the airplane flying east bound "at a slow rate of speed" and losing altitude. They observed the plane make a descending 180 degree turn and then disappear behind trees. One witness, located approximately 3 miles north of the accident site, observed the airplane over head and heard the engine "backfire and sputter." Another witness, located 1/4 miles north of the site, observed the airplane descending toward a tree line, pull up, reverse course, and descend into the ground.
According to the pilot, he had approximately 49 hours of total flight time at the time of the accident.
The aircraft was manufactured in 1978. According to airframe maintenance records, provided by the operator, the aircraft's total time in service was 4543 hours as of its last 100 hour inspection performed on October 20, 1995. The tachometer time recorded at the accident site was 4625.4 hours (82.4 hours flown since the last airframe inspection). A review of the maintenance records did not reveal any uncorrected maintenance defects and, according to the records, the airframe was in compliance with applicable airworthiness directives.
The engine was a Lycoming model O-235-L2C. According to engine maintenance records provided by the operator, and the tachometer time recorded at the accident site, the engine's total time in service was 4625.4 at the time of the accident. The last major overhaul (according to the records) of the engine was performed on October 29, 1987. The engine's time since major overhaul was 2552.4 hours at the time of the accident. The engine was operated 82.4 hours since the last 100 hour inspection performed on October 20, 1995. The engine manufacturer's recommended overhaul interval is 2,400 hours.
Both the pilot and witnesses reported gusty winds in the vicinity of the accident site. The nearest weather reporting facility, located approximately 25 nautical miles south of the accident site, reported winds from 130 degrees at 10 knots, gusting to 21 knots.
According to FAA records, there was no radio communications or distress calls from the aircraft; however, code "7700" was found dialed into the aircraft's transponder at the accident site.
WRECKAGE AND IMPACT INFORMATION
The initial ground scar, approximately 18 feet long (oriented approximately 036 degrees magnetic) and 8 inches wide, was found about 30 feet south of the wreckage. Fragments of the left wing tip, navigation lights, and paint chips corresponding to the leading edge were embedded along the length of the ground scar. Another ground scar, approximately 8 inches deep and 24 inches wide, was found about 18 feet south of the main wreckage. Both the propeller assembly and engine ring gear were found adjacent to this ground scar. The airplane main wreckage came to rest upright on a heading of 251 degrees magnetic, approximately 45 degrees nose down relative to the terrain. The propeller assembly was separated from the flange mount and mud was embedded into the spinner. One blade was found undamaged and the other blade was bent aft. The left wing leading edge was crushed aft along the span outboard from the wing support strut. Bending of the left wing strut (approximately 80 degrees) was observed, and the lower wing skin below the fuel tank adjacent to the strut was bulged downward. The left wing tip was destroyed. The leading edge of the right wing was crushed aft (less than the left wing) along the span outboard from the wing support strut. The tail section was found bent forward about 80 degrees and twisted to the left beginning just aft of the baggage compartment.
Primary and secondary flight control cable continuity from the cockpit to the control surfaces was confirmed. The flap actuator was measured and the flaps were confirmed to be in the down position (30 degrees). The fuel selector valve was found in the on position. Both throttle and mixture control levers were found in the "closed" position. The carburetor heat was found in the "off" position. Magneto select switch (keyed) was found in the "both" position.
The engine was removed from its mounts at the site for documentation purposes. The crankshaft was rotated and continuity to the accessory gears and valve action was confirmed (rocker box covers were removed to view valve action). There was thumb compression on all 4 cylinders. The top 4 spark plugs exhibited heavy wear, and 3 of the bottom plugs that were examined exhibited deposits on the electrodes (the #2 bottom plug had impact damage and could not be examined). The left and right magnetos were removed from the engine. The wire leads of the ignition harness assembly were cut by the investigation team at the distributor blocks and, when rotated by hand, produced spark at all 4 posts. The impulse coupling on the left magneto was not functioning.
The carburetor and carburetor intake manifold were removed from the engine. The fuel supply line was found separated from the carburetor and the carburetor inlet screen was attached. The throttle, mixture, and carburetor heat controls were attached. Fuel was found in the carburetor body. The throttle shaft was worn and the heat butterfly valve was found rubbing against the inside of the body and the seal was found partially worn. The float was the composite type.
The field examination of the airframe and engine did not reveal any pre-accident anomalies that would have prevented engine operation. Both fuel tanks had usable fuel and fuel odor was evident at the site.
MEDICAL AND PATHOLOGICAL INFORMATION
Toxicology tests on the pilot were negative for alcohol (carbon monoxide tests could not be performed due to a lack of a suitable specimen). Drug tests revealed the presence of Morphine (in urine) , Fentanyl ( in blood and urine), and Lidocaine (in blood and urine) in samples taken from the pilot. The samples were taken after the pilot was treated/medicated at the hospital.
There was no evidence of an in-flight or post impact fire.
TESTS AND RESEARCH
Fuel samples were retrieved for testing from the refueling truck which delivered 11.1 gallons of fuel to the aircraft prior to departure on the day of the accident. The samples, tested at Exxon Aviation Fuels, Houston, Texas, met the requirements of the ASTM D 910 Standard Specification for Aviation Gasoline 100LL. A sample retrieved from the aircraft at the accident site was visually observed to be clear, and visually void of water and sediment.
Carburetor ice probability charts were consulted given the approximate reported atmospheric conditions (temperature 45 degrees F, and dew point 29 degrees F). According to the charts, the carburetor was not within the probability range of becoming iced.
The engine (with accessories) was shipped to the manufacturer's facility to attempt engine operation under the supervision of the investigator-in-charge. Impact damage to the propeller mounting flange necessitated that it be straightened sufficiently to allow the installation of new bushings and a factory test propeller. A serviceable starter ring gear support assembly was installed. The impact damaged #2 bottom spark plug was replaced with a serviceable unit similar to the other plugs. The #2 cylinder was fractured near the intake port. The fracture was sealed with case putty. The rocker box covers, oil filter, and oil filter mounting base were replaced with new gaskets. A serviceable ignition harness assembly was installed (wire leads were cut at the accident site to hand test the magnetos).
On March 22, 1996, the engine, with original magnetos , carburetor, and spark plugs (except #2 bottom plug) was successfully operated in a factory production test cell. During engine operation, magneto checks resulted in 350 RPM drop and 145 RPM drop on the left and right magnetos, respectively (205 RPM difference). According to the manufacturer, the 350 RPM drop on the left magneto, and the 205 RPM difference in drop between the left and right magnetos, both exceeded test production test limits.
Subsequent bench testing of the left magneto revealed that the #3 bottom spark did not produce spark. The #3 spark plug had some deposits in the electrode area and a small piece of sealing surface was missing where the ignition wire attached. Testing of the plug in a spark plug test machine after removal of the deposits revealed that the plug did not fire. Further bench testing of the left magneto revealed that it would fire intermittently at speeds below 2000 RPM, and operated normally at higher speeds. Examination of the sparks plug electrodes revealed the following: #1 top was extremely worn; #1 bottom had heavy deposits; #2 top had moderate wear and light sooting; #2 bottom was fractured; #3 top was extremely worn; #3 bottom was extremely worn and had heavy deposits; #4 top was extremely worn; #4 bottom had moderate deposits.
During engine operation the carburetor was tested at 300 and 500 pounds per hour airflow. The engine attained 2360 RPM at the 500 pounds per hour test point. The carburetor was again tested on a different O-235-L2C engine. According to the manufacturer, full rich fuel flows during the test were within production test limits, except at 500 pounds per hour engine airflow. At that test point, fuel flow was 45.3 (.3 pounds per hour above the 45 pounds per hour limit). No anomalies were discovered with the carburetor that would have prevented its operation prior to the accident/impact.
Valve tappet clearances were measured on all valves. The #1 intake, #1 exhaust, and #3 exhaust valves had tappet clearances of .003 to .005 inches above the .012 inch maximum. The #4 intake valve tappet clearance was measured at zero. According to the manufacturer's Service Instruction No. 1068A, tappet clearance of .010 inch is desirable, however a range of .006 inch to .012 inch is acceptable. The Service Instruction also recommends that tappet clearances be checked at 100 hour inspection intervals. All exhaust and intake valves moved freely within their guides.
During a differential compression test, the #4 cylinder had a differential compression of 61/80 PSI. Differential compression on the #1, #2, and #3 cylinders were measured within 72 to 73/80 PSI. All cylinder and piston domes exhibited normal wear.
Other than the aforementioned valve tappet clearance anomalies, and the general worn condition of the spark plug electrodes, no conclusive evidence of a mechanical engine malfunction was discovered during the engine test run or physical examination of components. According to the manufacturer, the combination of the worn spark plugs and the out of tolerance valve tappet clearances, engine performance could have been intermittently affected; however, the degree to which the pilot described the RPM drop during the flight could not be reproduced in the test cell or substantiated during detailed examination.
The wreckage was released to the owner's representative.