On December 9, 2010, at 1645 eastern standard time, a Flight Design GMBH, CTLS, N30LK, operated by Zone Aviation, received substantial damage on impact with terrain during a forced landing near Willard, Ohio. The pilot reported that the airplane experienced a total loss of engine power during cruise flight. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 91 personal flight was not operating on a flight plan. The private pilot was uninjured and the passenger sustained minor injuries. The flight originated from Union County Airport, Marysville, Ohio, at 1620 and was en route to Lorain County Regional Airport, Lorain/Elyria, Ohio .

The pilot had rented the airplane from the operator so as to accumulate cross country flight time requirements for an instrument rating. The pilot preflighted the airplane and noted that the oil was at the dip stick's upper quantity line. There were no mechanical anomalies observed. After takeoff, he climbed to 10,000 feet mean sea level (MSL) and then descended to 9,500 feet MSL where the airplane remained for approximately 10 minutes. A "snap or pop" sound then occurred. The engine immediately began vibrating; actuation of carburetor heat had no effect. The engine speed decreased from 5,150 rpm to 4,000 rpm with the engine throttle setting remaining unchanged at about 85 percent. The engine subsequently experienced a total loss of engine power. The propeller stopped rotating during the entire descent and subsequent forced landing.

The airplane was powered by a Rotax 912 ULS2, serial number 5651168, engine that underwent its last 100-hour/annual inspection at a total time of 503.7 hours, on October 20, 2010. The engine received its last oil and oil filter change using Aeroshell Sports Plus 4 oil at a total time of 558.1 hours on November 30, 2010.

Engine logbook records show that the oil and oil filter were changed on the following dates, tachometer times, and with the following oil brands:

December 22, 2009, 54.5 hours, Aeroshell Sports Plus 4
March 2, 2010, 130.3 hours, Aeroshell Sports Plus 4
May 13, 2010, 187.9 hours, Penzoil 20W50 Motorcycle
June 10, 2010, 190.8 hours, Penzoil 20W50 Motorcycle
July 1, 2010, 303.8 hours, Penzoil (type not specified)
July 20, 2010, 349.7 hours, Aeroshell Sports Plus 4
August 20, 2010, 406.5 hours, Aeroshell Sports Plus 4
September 23, 2010, 453.8 hours, Aeroshell Sports Plus 4

There were no engine logbook entires showing any repair or replacement of engine components prior to the accident. The operator stated the engine had never experienced a propeller strike.

The airplane was examined at the operator's base of operations under the supervision of the Federal Aviation Administration. The examination noted that the engine and engine firewall were intact and attached to the fuselage. The fuselage sustained substantial damage . The engine crankshaft could not be rotated by hand with the spark plugs removed. Appearance of the spark plugs were consistent with normal engine operation. The number 3 spark plug was damaged. The engine oil level measured by the dipstick was in the normal operating range. The oil tank was disassembled and the oil level within the oil tank was in the normal range. The oil filter did not contain metallic debris. The cooling system appeared intact and there was no evidence of cooling leaks. The engine valve train did not display indications of hammering. Cylinder head numbers 1, 3, and 4 did not display indications of hammering.

The number 3 piston was fragmented. The exhaust valve was fractured at the head/stem area. The exhaust spring was fractured in half. The cylinder wall was scoredand the piston skirt was broken. The intake valve was intact except for a triangular piece that was broken off at the valve seat. The connecting rod was twisted with the piston pin offset 3/4 from the connecting rod. The crankshaft was twisted between the main webs.

There was no blue discoloration consistent with oil starvation. The crankcase, main bearings, camshaft, and lifters displayed normal features. Metal debris from the number 3 cylinder was found throughout the crankcase. The gearbox displayed normal features and contained metal debris from the number 3 cylinder.

Metallurgical examination of the number 3 cylinder exhaust valve spring, part number 838155, revealed a fatigue fracture due to a non-metallic inclusion. The fatigue fracture originated at the coil side face and covered about 25 percent of the material cross-section. The fatigue fracture initiated at a depth of about 210 microns below the spring surface. The inclusion was above the metallographic wire rod inspection limit of 15 microns.

Rotax referenced the International Valve Spring Wire Manufactures Association in stating:

“Inclusions are unavoidable imperfections in steel. Regardless of the steelmaking method, some type of undesirable inclusion will exist.”
“Most valve spring quality wire specifications that have been written in the last several years limit the allowed inclusion thickness at 15 or 20 microns, when inspected using optical methods. Other types of inspection, such as acid dissolution and fatigue testing, have confirmed that good quality steels produced with the new technology will certainly contain inclusions larger than 15 microns. One example of an acid dissolution test has shown that a 25 gram sample of today’s cleanest steel contained as many as 14 harmful inclusions in the size range 20-50 microns.”

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