NTSB Factual Report

On August 13, 2001, about 1200 eastern daylight time, a Cessna 210L, N732JT, sustained minor damage during a catastrophic engine failure while in cruise flight near Bluefield, West Virginia. The certificated private pilot was not injured. Visual meteorological conditions prevailed and an instrument flight rules flight plan had been filed for the flight that departed the Manassas Regional Airport (HEF), Manassas, Virginia, about 1005, destined for the McGhee Tyson Airport (TYS), Knoxville, Tennessee. The personal flight was conducted under 14 CFR Part 91.

The pilot reported that he was in cruise flight at 8,000 feet, when he experienced a slight vibration. Shortly thereafter, he experienced a propeller over-speed, and a total loss of oil pressure. The pilot declared an emergency and requested vectors to the nearest airport. The engine vibration increased and when the airplane was about 2 miles from the Mercer County Airport (BLF), Bluefield, West Virginia, he observed flames coming from the engine cowling. Additionally, the cockpit began to fill with smoke. The pilot shut the engine down, and performed a forced landing to runway 23, at BLF.

On scene examination of the IO-520L engine revealed a three inch hole in the engine case, adjacent to the number 2 cylinder. The engine was retained and shipped to Teledyne Continental Motors (TCM), Mobile, Alabama, for further examination.

According to maintenance records, the airplane had been operated for about 4 hours since an annual inspection, which was performed on August 3, 2001. At that time, the number 1 and 2 cylinder and piston assemblies were replaced. In addition, the intake and exhaust valve lifters for all the cylinders were also replaced. The maintenance was performed by Piedmont-Hawthorne Aviation, Knoxville, Tennessee.

A teardown of the engine was performed at TCM under the supervision of a Federal Aviation Administration inspector. The number 2 connecting rod was separated from the crankshaft and pieces of the connecting rod assembly and other metallic debris were located in the oil sump.

All cylinders were steel barreled, plus .010-inch oversized. The number 2 cylinder bore exhibited scoring and piston material was observed embedded in the cylinder bore. The number 2 piston, which was manufactured by Superior Air Parts, Coppell, Texas, was heavily scored on the piston skirt and the piston pin plug was broken at the engine forward side, at the steel pin. Additionally, the number 2 piston bore was elongated on both sides of the piston pin boss. With the exception of the number 2 piston pin assembly, all other piston pin assemblies exhibited normal operational signatures.

The number 1 and 3 connecting rod bearings exhibited some deformation consistent with lubrication distress. The number 1 and 2 connecting rod journals were discolored consistent with heat due to lubrication distress. All other crankshaft main and connecting rod journals exhibited normal operational signatures.

The engine camshaft and valve lifters exhibited normal operation signatures, with no lifter spalling or camshaft wear.

During the teardown, the number 2 piston was measured with a micrometer and found to be a standard size when compared to the appropriate TCM piston drawing. The number 2 cylinder bore was measured .010-inch oversize.

The number 1 and 2 cylinder pistons, the number 2 cylinder, the number 2 connecting rod and associated connecting rod debris, were forward to the Safety Board Material's Laboratory, Washington, DC, for further examination.

Examination of the components by a Safety Board Metallurgist’s revealed that the number 2 cylinder assembly was generally intact with no damage apparent to the valve train components; however, heavy longitudinal scoring and metal transfer was apparent on the bore of the cylinder barrel and the inboard edge of the barrel was deformed consistent with connecting rod contact.

The inboard end of the number 2 connecting rod was fractured in two locations adjacent to the rod bearing area, and the surrounding area was discolored consistent with extreme localized heating. One smaller piece of the connecting rod and one bolt fragment were also received; however, no portion of the cap or other bolt pieces were submitted. Post fracture damage completely obliterated one of the rod fractures and severely damaged the other; however, sufficient detail remained to indicate high stress fatigue propagation from the outer surface of one fracture. The fatigue initiated on the bolt cutout surface and progressed a short distance into the rod before final overstress separation. There were also indicators of severe heating at the bearing surface prior to the separation. The connecting rod bolt fragment showed tensile elongation along with surface and fracture features consistent with an elevated temperature overstress separation.

The crowns of both pistons were marked with part numbers "SA631475" and "010," which indicated that they were manufactured by Superior Air Parts and were 0.010 inch oversize (P010) in diameter. Further markings on the piston pin bosses identified both pistons as SA631892 forgings from lot KS133002. Both sides of the number 2 piston pin bore were severely enlarged and elongated; however, the forward side was larger then the aft side. Additionally, the surrounding areas of the piston were heavily damaged. The engine forward side of the aluminum pin plug, was fractured within the pin body, and the separated plug piece was worn and deformed into an "egg shaped" piece. The separated pin plug wore and deformed pockets into the sides of the piston. The skirt of the piston was severely scored and the rings were trapped and fractured in their respective grooves.

The number 1 piston displayed the same identification markings as the number 2 piston and had similar, but less severe levels of damage.

Diameter measurements were made on each piston at various datum points indicated on a Superior Air Parts engineering drawing, using an optical comparator. The measurements revealed that the number 1 piston contained two locations that were within the P010 limits, and overall tended to be closer to the P010 dimensions. The number 2 piston was closer in size to a standard piston and did not contained any measurable dimensions within the P010 limits.

Additional testing of the pistons included electrical conductivity and hardness measurements. Conductivity measurements of the number 1 piston revealed "fairly uniform" conductivity averaging 47.2% International Annealed Copper Standard (IACS). Conductivity testing of the number 2 piston ranged from a low of 39.0 % to a high of 45.5 % IACS. Typical electrical conductivity for the material was 40 % IACS. All hardness measurements taken from both pistons were below the specified range for a new piston.

Further review of maintenance records revealed the cylinder assemblies installed by Piedmont Hawthorne Aviation, were supplied by Gibson Aviation, El Reno, Oklahoma, and built with used "serviceable parts." According the owner of Gibson Aviation, the pistons supplied to Piedmont-Hawthorne Aviation were "used serviceable pistons that meet the oversized specification." The specific service history of the pistons and piston pins could not be determined. The owner of Gibson Aviation also stated that Gibson Aviation did not check the "piston skirt clearance" and expected the installer to check the skirt clearance per the TCM Overhaul Manual, at the time of the installation. A representative from Piedmont-Hawthorne Aviation stated that the cylinders were installed per the TCM overhaul manual.

NTSB Probable Cause

Improper maintenance which resulted in the installation of an unserviceable piston assembly, and the subsequent catastrophic engine failure. Factors in this accident were the improper inspection by the piston supplier and the softening of the piston.