CLANTON, AL, USA
N6937Y
Piper PA-23-250
During cruise flight at 6,000 feet, the pilot reported to air traffic control that he had an engine fire and needed to land immediately. Subsequently, the airplane's left wing separated in-flight, and the airplane crashed in an uncontrolled descent. An investigation revealed that the number six cylinder on the left engine had separated in-flight. Metallurgical examination of the cylinder revealed a fatigue fracture. The fatigue originated at a corrosion pit between the cylinder's cooling fins. There was evidence that fire erupted and spread to the left wing fuel tank, leading to separation of the wing. Also, heat streaking was noted on the left engine cowling and left horizontal stabilizer. Aircraft records showed that the engine had accumulated 1,682 hours of flight time since it was last overhauled on 5/19/75.
HISTORY OF FLIGHT On June 23, 1996, about 2027 central daylight time, a Piper PA-23-250, N6937Y, came apart in-flight, after the pilot reported an in-flight fire, five miles south of Gragg-Wade Field, near Clanton, Alabama. The business flight was operated under the provisions of Title 14 CFR Part 91 with a valid instrument flight clearance. Visual weather conditions prevailed at the time of the accident The private pilot and the four passengers were fatally injured, and the airplane was destroyed by fire and impact forces. The flight departed Lakeland, Florida, at 1900 eastern daylight time. During cruise flight at 6,000 feet, the pilot reported to Montgomery Approach Control that the airplane was on fire, and that he needed to land. The air traffic controller told the pilot that Gragg-Wade Field was located five miles in his twelve o'clock position. The pilot requested the radio frequency that controlled the runway lights. When the controller attempted to respond to the pilot's request, there was a simultaneous loss of radar and radio contact. The scattered wreckage of the airplane was located about three miles south southeast of Clanton, Alabama. Airplane debris was scattered over an area about one half mile long, with the left engine and nacelle, and the left wing outboard section separated from the main wreckage. PERSONNEL INFORMATION According to information contained in the pilot's log, he obtained his private pilot certificate on January 25, 1994. His airplane single engine rating was obtained the same day. On November 2, 1994, he was issued a multi-engine rating, and an airplane instrument rating on April 6, 1995. According to entries in the log, the pilot obtained an initial checkout in the same make and model airplane on September 15, 1994. Additional information regarding the pilot is contained in NTSB Form 6120.4, page 3, under the heading titled First Pilot Information. The flight hours listed in the NTSB Form 6120.4 were obtained from the pilot's log. The last flight listed in the log was dated June 14, 1996. AIRCRAFT INFORMATION The airplane records indicated that the transponder, altimeter, and the static system were tested on May 1, 1995. According to the aircraft records, the last annual inspection was conducted on May 24, 1996, at a total aircraft time of 3,534.18 hours. The total flight hours at the time of the accident could not be determined. The airplane was powered by two Lycoming IO-540-C4B5 engines. The left engine log, engine, serial number L-7502-48, indicated 3,534.18 total hours at the last annual inspection, with 1,682.22 hours since major overhaul. The engine log entry for the last annual inspection indicated that the oil and filter were changed and included the comment "-no metal-." An entry was found in the left engine log dated May 19, 1975, which indicated that the engine was removed and disassembled. According to the log entry, the engine was cleaned, all steel parts magnafluxed, two piston pins replaced, one piston replaced, and all cylinders had the glaze removed from the cylinder walls. All exhaust valve guides were replaced, all lifter bodies replaced, and all intake and exhaust valves, springs and keepers were replaced. The log entry indicated that the total time of the engine was 1,852 hours, and the time since major overhaul was listed as zero. An entry in the aircraft log, also dated May 19, 1975, indicated that both engines and propellers were overhauled. According to Lycoming Service Instruction No. 1009AJ, dated July 1,1992, the recommended time between overhauls for the IO-540C engine is 2,000 hours. Meteorological Conditions Visual weather conditions existed at the time of the accident. Additional information is contained in the NTSB Form 6120.4, on page 4, under the heading, Weather Information. Wreckage and Impact Information The main wreckage, which excluded the left wing outboard of the engine nacelle, left engine and nacelle, and the left propeller, was located in a grassy field. The main wreckage occupied a crater that was about six feet deep. The fuselage, empennage, and right wing exhibited accordion like crushing along the airplane's longitudinal axis. The right engine was buried, with both propeller blades broken out of the propeller hub. The right propeller blades were bent, spanwise, in a broad arc, and exhibited leading edge gouges. There were visible signs of heat streaking on the left horizontal stabilizer. The left wing outboard section was located about 200 yards southeast of the main wreckage. There was evidence of heat distress that included charring of the left fuel bladder, blackening of the interior of the wing leading edge skin, and bulged deformation, away from the fuel bladder, of wing structure around the bladder. The left engine and cowling was located about 1,000 yards south of the main wreckage on the shoulder of U. S. Highway 31. Both propeller blades were in place in the feather position. Heat streaks were noted on the left rear portion of the cowling. The number six cylinder was broken off and separated from the engine and was found adjacent to it, still shrouded by the cowling. The cylinder had separated circumferentially at the approximate midpoint of the steel barrel fins. The oil sump was crushed and oil was saturated through out the compartment. The bent but unbroken connecting rod was attached to the crankshaft, the piston and piston pin were found separated and to the side, with the piston boss broken. The piston crown exhibited peening marks that corresponded to the shape and diameter of the separated cylinder. MEDICAL AND PATHOLOGICAL INFORMATION A post mortem and toxicology examination of the pilot was conducted by the Alabama Department of Forensic Sciences, Office of the Medical Examiner, James R. Lauridson, MD, P. O. Box 240591, Montgomery, Alabama, 36124-0591. A toxicology examination of the pilot was also conducted by the Federal Aviation Administration Toxicology and Accident Research Laboratory P.O Box 25082, Oklahoma City, Oklahoma 73125. The report stated that ethanol found in this case is most likely from post mortem ethanol production. TESTS AND RESEARCH The separated number six cylinder was examined at the Safety Board's Materials Laboratory in Washington, D. C. The cylinder separated circumferentially between the 8th and 9th cooling fins, counting from the head interface. The fracture contained crack arrest positions indicative of fatigue progression. Both fracture faces were covered with heavy accumulations of dark combustion deposits. The fatigue cracking originated at a large corrosion pit. ADDITIONAL INFORMATION The airplane wreckage and records were released to the registered owner's insurance representative, Kevin Twiss of Aviation Insurance Group 1255 Roberts Boulevard, Suite 200 Kennesaw, GA 30144.
corrosion pitting of the number six cylinder on the left engine, and subsequent fatigue fracture and separation of the cylinder, which led to an engine compartment fire, wing fire, and an in-flight separation of the left wing.
Source: NTSB Aviation Accident Database
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