Accident Summary
On September 17, 2015, at approximately 1330 central daylight time, a Cessna R172 airplane, registration N180CM, was substantially damaged during a forced landing near Easterwood Field Airport (KCLL) in College Station, Texas. The airline transport pilot and passenger sustained serious injuries. The personal flight was conducted under 14 Code of Federal Regulations Part 91 on a VFR flight plan. Visual meteorological conditions prevailed. The cross-country flight had departed Thompson Field Airport (1TA7) in Canton, Texas, and was en route to Mustang Beach Airport (KRAS) in Port Aransas, Texas, but diverted to KCLL.
The pilot reported that at 6,500 feet, a loud "pop or bang" was heard, followed by vibrations and a subsequent loss of engine power. During the forced landing attempt to a road, the airplane struck a building and then a truck. The right wing and fuselage were bent and buckled.
Engine Examination
An examination of the engine, a Teledyne Continental Motors IO-360-K (serial number 355189), was conducted under the auspices of the NTSB investigator-in-charge. Two holes were found in the crankcase: one about 1 inch wide and 4 inches long directly aft of the #1 cylinder, and another 1 inch wide and 1 inch long directly aft of the #2 cylinder.
Internal examination revealed that the #1 connecting rod was fragmented, with pieces found throughout the engine and in the oil sump. The beam width of the failed connecting rod measured 0.6165 inches, while the remaining rods measured between 0.5960 and 0.6110 inches. Metallurgical examination of a separation point at the I-beam of the rod showed signatures consistent with fatigue. No further anomalies were found in the airframe or remaining systems.
Service Bulletins and Maintenance History
On May 28, 1986, Teledyne Continental Aircraft Engine issued Service Bulletin (SB) M86-11, "Connecting Rod Product Improvement." It stated that during maintenance allowing access to connecting rods, they should be measured and replaced if their dimension fell below 0.625 inches. The accident airplane's engine was included in the serial number range provided in this SB, and the forging signature on its connecting rods was also included.
On October 1, 1986, Revision 1 to SB M86-11 changed the affected serial number range, excluding the accident airplane's connecting rods by engine serial number but not by forging signature identification. According to Continental Motors, the serial number range was reduced based on production records indicating those serial numbers likely would not have the affected rods.
On November 14, 1996, Critical Service Bulletin (CSB) 96-13 superseded M86-11 Revision 1. It required inspection at the next 100-hour or annual inspection, but no later than 1 year following issuance. This CSB excluded the accident engine's serial number and did not discuss the forging signatures that would have still required inspection under the previous SB.
Maintenance records showed the engine was overhauled on February 1, 1991. Engine components, including connecting rods, were sent to Engine Components, Inc., for inspection and repair. New main and rod bearings were installed, but the original connecting rods were reused. No entry showed compliance with either the SB or CSB. From 1991 until the accident, no further disassembly of the engine or cylinders occurred that would have allowed inspection of the connecting rods.
The Teledyne Industries IO-360 Overhaul Manual, current at overhaul, also provided a serviceable limit dimension of 0.625 inches for the connecting rod beam at its narrowest point. There was no indication of what service information or manuals the mechanic(s) used or had available during the overhaul.