CEN10LA131

The pilot reported that he was in level cruise flight at 3,500 feet mean sea level when the engine suddenly vibrated then seized. The pilot made a "firm" forced landing on rolling brush and rock-strewn terrain. During the landing roll, the landing gear was sheared off and the canard wing was crushed. Engine disassembly revealed case fretting and main bearing movement. A representative of the engine manufacturer indicated that the failure mode was extremely rare, if not unique. The pilot had installed a Hertzler “Silver Bullet” composite propeller to the extended hub. According to the representative, it was possible that a harmonic vibration could have emanated from the propeller through the extended hub to the crankshaft. However, this propeller had not been tested to determine if there were amplified propeller harmonics to the crankshaft and the investigation was unable to determine that such vibration led to the engine failure.

On February 28, 2010, approximately 1845 central standard time, a Lacour Long-EZ SR7-1, N97EZ, registered to and operated by the pilot, was substantially damaged when it impacted terrain during a night forced landing after the engine seized in cruise flight near Falfurrias, Texas. Visual meteorological conditions prevailed at the time of the accident. The personal flight was being conducted under the provisions of Title 14 Code of Federal Regulations (CFR) Part 91 without a flight plan. The pilot and passenger on board the airplane were not injured. The cross-country flight originated at San Antonio (SAT), Texas, approximately 1800, and was en route to McAllen (MFE), Texas. The pilot said he was in level cruise flight at 3,500 feet msl when the engine suddenly vibrated then seized. The pilot lowered the nose gear and made a forced landing on rolling brush and rock-strewn terrain. Touchdown was "firm." During the landing roll, the landing gear was sheared off and the canard wing was crushed. On April 23, 2010, the engine was disassembled and inspected at Cutter Aviation in San Antonio, Texas, under the direction of an FAA airworthiness inspector. Although no metallic particles were found in the drained crankcase oil, some were found in the suction oil screen. The oil filter was relatively clean. The vacuum pump’s nylon drive shaft was sheared. Upon removal of the accessory drive case cover, it was discovered that the small drive gear had been thrust approximately 1/8” out of alignment with the other drive gears. Number 4 cylinder and piston showed unusual wear and discoloration. Inspection of the crankshaft revealed it had sheared at the rear of the number three connecting rod journal. A metallurgical examination of the crankshaft was conducted on May 22, 2010, by AADFW Laboratories in Euless Texas. The sample had cracks and three linear indications. There were no hardening indications. “Multiple origin fractures, possible from over stress” were noted. The back sides of the main bearing shells were very shiny, indicative of bearing movement and loose thru-bolt torque. Case fretting was noted in the center main bearing saddle parting surfaces. The report said that the surface origin of the fatigue fracture was in the aft radius of the #3 rod Journal, initiating at approximately 15 degrees after top dead center. “This position is approximately where the maximum power loading would take place during engine operation,” the report said. “Engine timing will have an effect on the exact position of the maximum power loading. Normal engine timing would be 25 degrees BTC. The actual ignition timing is unknown. Advanced timing, such as used with the electronic ignition, is known to produce increased heat, increased power, and increased pre-ignition and detonation probability.” No material defects and no manufacturing issues, such as grinding burn, were found. No assembly issues, such as fillet ride or connecting rod to journal fit, were found. The reportlisted possible causes of the bearing movement and case fretting: (1) maintenance on the ignition system, (2) vibratory stresses from an incompatible combination of propeller and engine, (3) an out-of-balance or out-of-track propeller, and (4) previous damage to the propeller. The report concluded, “This investigative analysis has been unable to determine the root cause of what initiated the fatigue fracture in this crankshaft.” All engine parts were PMA (Parts Manufacturer Approval) certified. PMA is a combined design-production approval, and is required for the production, replacement, or modification of engine parts for sale or installation on type-certificated engine models approved under supplemental type certificates (STC)]. According to Aero Sport Power, this was the first time an O-320-D2A had experienced this type of a failure. It was noted that the pilot had made numerous engine modifications to improve cooling, and utilized extra cylinder head baffles. A non-standard oil pan was installed to accommodate the Long EZ fuselage. The pilot had also installed a Hertzler “Silver Bullet” composite propeller to the extended hub. According to Aero Sport Power, this propeller had not been tested to determine if there were amplified propeller harmonics to the crankshaft. Aero Sport Power recommended a propeller made of wood and heavier than the composite propeller, giving the propulsion system more of a flywheel effect. Aero Sport Power noted that a propeller flies in “dirty air”; that is, it is subject to airflow dynamics generated by the Long-EZ’s canard and wings. Aero Sport Power said it was possible that a harmonic vibration could emanate from the propeller through the extended hub to the crankshaft. FAA Advisory Circular 20-103, dated March 7, 1978, addresses this issue.