SEA03FA025

The pilot reported that while en route, the engine backfired, followed by a total loss of power. The pilot initiated a forced landing, attempting to land at a nearby airport. The aircraft was unable to reach the runway and collided with trees and brush about 200 yards short of the runway. During a post-accident engine examination, the crankshaft was found fractured through the forward side of the number four journal. Metallurgical examination of the fracture surface revealed that the crankshaft failure was the result of fatigue initiating at a subsurface inclusion. Scanning electron microscopic examinations established that the fatigue initiated at a single subsurface site located 0.023 inch below the journal surface. Closer inspection found an approximate 0.002 to 0.003 inch diameter pit at the origin location. The pit was mostly empty but contained remnants of material that was identified by energy dispersive x-ray spectroscopic as mostly aluminum and calcium. The age of the crankshaft could not be determined but appeared to be an older crankshaft that was manufactured prior to the manufacturers transition to vacuum arc remelted steels which have higher fatigue strengths and which almost eliminates the presence of inclusions.

History of flight

On January 12, 2003, approximately 1547 Pacific standard time, a Mooney M20F, N6442Q, registered to and being flown by a private pilot, sustained substantial damage during a collision with trees/terrain during an intentional gear-up landing following a total loss of power on short final to the Tacoma Narrows Airport, Tacoma, Washington. Visual meteorological conditions prevailed and no flight plan had been filed. The pilot was uninjured during the forced landing. The flight, which was personal, was operated under 14 CFR 91, and originated from Puyallup, Washington, approximately 1530, and was destined for Olympia, Washington.

During a telephone interview and subsequent written statement, the pilot reported that while en route to Olympia about 1,000 feet altitude and northwest of Tacoma Narrows, the engine backfired, followed by a total loss of power. The pilot contacted Tacoma Narrows tower requesting landing. The pilot was cleared to runway 17. The pilot reported that he intentionally kept the landing gear retracted in hopes of extending the glide path to the runway, however, the aircraft was too low and collided with high brush and the terrain about 200 yards short of the runway.

Personnel information

At the time of the accident, the pilot held a private pilot certificate for single engine land and sea aircraft with an instrument rating. The pilot reported a total flight time in all aircraft of 2,279 hours with 2,000 hours in the make and model aircraft involved in the accident.

Aircraft information

The aircraft and engine maintenance logbooks were provided for review. The engine logbook indicated that the Lycoming IO-360-A1A, serial number L14312-51A engine had been overhauled on October 1, 1998, at a tach time of 3,184 hours. Total time on the engine at the time was 1,350 hours. The engine was installed in N6442Q on November 29, 1998.

The next entry was for an annual/100 hour inspection dated April 7, 2000, at a tach time of 3,276.22 hours and 92.22 hours since major overhaul (SMOH). No significant write-ups were recorded at the time.

On July 11, 2001, at a tach time of 3,377.52 hours and 193.52 hours SMOH, the engine was signed off for an annual/100 inspection. Total time on the engine was recorded as 3,294.52 hours. The logbook entry stated in part, "Drained oil, removed oil screen, cleaned screen (two small pieces of metal), replaced screen and added 8 qts W100 50W Aeroshell oil." The mechanic who accomplished the maintenance inspection reported that the metal appeared to be two small pieces of steel shavings that were not aluminum. The mechanic stated that he asked the pilot to bring the aircraft back after a few hours of flight time. The pilot did not bring the aircraft back until August.

Another entry in this same inspection reported, "Inspected fuel filter, found debris, removed fuel pump and removed debris." The mechanic reported that the debris appeared to be fuel hose material. The mechanic further stated that it appeared that the hoses had not been changed at overhaul and there were signs of deterioration.

On August 3, 2001, at a tach time of 3,379.59 hours and 195.59 hours SMOH, the aircraft was brought to the same mechanic. During this maintenance visit, the oil hoses and fuel lines were removed and replaced. The mechanic reported that the pilot stated that during the last flight before bringing the aircraft in to get the hoses changed, the fuel pressure fluctuated.

On October 29, 2001, at a tach time of 3,394.59 hours and 210.59 hours SMOH, the aircraft was brought to the same mechanic. During this maintenance visit, the mechanic stated that he inspected the engine for an oil leak. The mechanic stated that he tightened the sump bolts, case bolts and intake manifold bolts. All appeared to be tight. The leak appeared to be coming from the case half near the nose.

On April 4, 2002, at a tach time of 3,415.4 hours and 231.4 hours SMOH, the aircraft was brought to the same mechanic to re-check for oil leaks. The logbook entry stated that the mechanic "Removed lower case bolts and reinstalled using sealant," and "Replaced intake gaskets on cylinders #2 and #4."

The mechanic stated that there was still an oil leak when the aircraft was brought in. The mechanic found that one of the case bolts was where the leak was coming from. He stated that he also checked a few of the cylinder bolts (not all). The ones that he checked all seemed fine and that at the end of the inspection the leak went away.

At the time of the accident, the tach time was recorded as 3,473.78 hours and 290.1 hours SMOH. The aircraft and engine had not accomplished an annual/100 hours inspection since July 11, 2001.

Wreckage and impact information

The wreckage was located approximately 200 yards short of runway 17, and approximately 100 yards east of runway centerline. The aircraft collided with high brush and trees. Extensive leading edge damage was noted to both wings. The landing gear was retracted. All flight control surfaces remained attached.

Additional information

On January 16, 2003, investigators with the National Transportation Safety Board, Federal Aviation Administration and Lycoming Engines, examined the engine. During the inspection it was found that the left magneto was separated from the mount. A section of the mount was missing and broken away. Both attachment bolts were missing as well as the gasket. Evidence of rubbing was noted on the mounting flange. The right side magneto remained attached at the mount. Both magnetos were removed. Both magnetos produced a spark from all towers utilizing hand rotation. During the removal and inspection of the remainder of the accessories, the oil screen was found to contain a significant amount of metal flakes on the screen. The oil pump drive was broken. After removal of all accessories and accessory housing, it was found that the crankshaft bolt was loose. The dowel pin was intact. Rotation of the crankshaft did not produce accessory continuity.

On January 21, 2003, the engine was completely torn down. During the teardown, it was found that the piston skirts were scratched from internal metal foreign object debris. The camshaft was fractured between the number four intake and exhaust lobes. It appeared that the fracture was a result of a connecting rod strike. The numbers three and four pistons also displayed rod strikes. The crankshaft was fractured in the area of the number four connecting rod journal. The number four connecting rod remained attached and the two rod bolts, rod nuts and cap were intact. The number 4 connecting rod bearing was completely worn down, and the metal on the connecting rod was galled. Significant fretting was noted on the crankcase halves in the areas of the rear and center saddle supports. The oil sump, suction screen and oil pressure screen contained what appeared to be the bearing metal from the number four connecting rod. The sump also contained the material from the missing left magneto gasket.

The crankshaft and number four connecting rod were sent to the National Transportation Safety Board Materials Laboratory, Washington D.C. for examination. The metallurgist reported that the crankshaft failure was the result of fatigue initiating at a subsurface inclusion. Scanning electron microscopic (SEM) examinations established that the fatigue initiated at a single subsurface site located 0.023 inch below the journal surface. Closer inspection found an approximate 0.002 to 0.003 inch diameter pit at the origin location. The pit was mostly empty but contained remnants of material that was identified by energy dispersive x-ray spectroscopic (EDS) as mostly aluminum and calcium. Additional SEM imaging utilizing backscattered electrons identified several additional imbedded particles (inclusions) of aluminum and calcium in the area of the fat