College Station, TX, USA
N180CM
CESSNA R172
The airline transport pilot was conducting a personal cross-country flight. The pilot reported that, during cruise flight, he heard a loud "pop or bang" and that the airplane started vibrating. The engine subsequently lost power. During the forced landing to a road, the airplane struck a building and then a truck. An examination of the engine found two holes in the crankcase. Further examination revealed that the No. 1 connecting rod had failed due to fatigue. The engine manufacturer had previously issued a service bulletin (SB), which recommended the examination and potential replacement of the connecting rods in the accident engine due to wear or fatigue; the SB included both the accident engine's serial number and the connecting rod's forging stamp identification. The engine manufacturer subsequently revised the SB; the revision excluded the accident engine by serial number but the connecting rods were still included. However, it would not be possible for a mechanic to identify the connecting rod serial numbers without taking the engine apart. A review of the maintenance records revealed that the accident engine was last overhauled about 5 years after the issuance of the revised SB; no entry was found indicating that the connecting rods were examined in accordance with the SB, and no subsequent maintenance occurred that would have allowed for the examination of the connecting rods. However, because this was a Part 91 operation, such an inspection was not mandatory. Despite the fact that the SB was not mandatory, because the manufacturer removed the engine serial number from the revised SB, a mechanic would have very little way of knowing whether the connecting rods should be inspected.
On September 17, 2015, about 1330 central daylight time, a Cessna R172 airplane, N180CM, was substantially damaged during a forced landing near Easterwood Field Airport (KCLL), College Station, Texas. The airline transport pilot and passenger sustained serious injuries. The personal flight was conducted under the provisions of 14 Code of Federal Regulations Part 91 on a visual flight rules flight plan. Visual meteorological conditions prevailed at the time of the accident. The cross-country flight departed Thompson Field Airport (1TA7), Canton, Texas, was en route to Mustang Beach Airport (KRAS), Port Aransas, Texas, and diverted to KCLL. The pilot reported that the airplane was at 6,500 feet when he heard a loud "pop or bang" and the airplane started vibrating. The engine subsequently lost power. The pilot was performing a forced landing to a road when the airplane struck a building and then a truck. The right wing and fuselage were bent and buckled. The engine exmination was conducted under the auspicies of the National Transportation Safety Board investigator-in-charge. The accident engine was a Teledyne Continental Motors IO-360-K engine (serial number 355189). An examination of the engine found a hole in the crankcase, about 1 inch wide and 4 inches long, directly aft of the #1 cylinder. A second hole, one inch wide and 1 inch long, was directly aft of the #2 cylinder in the crank case. Internal examination of the engine revealed that the #1 connecting rod was fragmented. Pieces of the rod were found throughout the engine and in the oil sump. The beam width of the failed connecting rod was measured at 0.6165 inches. The remaining connecting rods measured between 0.5960 and 0.6110 inches. Metallurgical examination of a separation point at the I-beam of the rod revealed signatures consistent with fatigue. An examination of the airframe and remaining systems revealed no further anomalies. On May 28, 1986, Teledyne Continental Aircraft Engine issued Service Bulletin (SB) M86-11 - Connecting Rod Product Improvement. This stated in part that during maintenance, which allowed access to the connecting rods, the connecting rods should be measured and replaced if their dimension fell below a dimension of 0.625. The accident airplane's engine was included in the serial number range provided in this SB. In addition, the forging signature on the accident engine's connecting rods was also included in this SB. On October 1, 1986, Teledyne Continental Aircraft Engine issued Revision 1 to SB M86-11. This revision changed the affected serial number range and excluded 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 upon production records that indicated that those serial numbers would likely not have the affected connecting rods installed. On November 14, 1996, Teledyne Continental Motors issued Critical Service Bulletin (CSB) 96-13. This CSB superseded M86-11 Revision 1. This CSB required the inspection to take place at the next 100 hour or annual inspection but no later than 1 year following the issuance of the CSB. This CSB excluded the accident engine's serial number and did not discuss the forging signatures which would have still required the connecting rod be inspected and replaced according to the previous SB. According to the maintenance records, the engine overhaul was completed on February 1, 1991. The engine components, including the connecting rods, were sent to Engine Components, Inc., for inspection and repair as necessary. New main and rod bearings were installed and the original connecting rods were used. There was no entry in the maintenance records showing compliance with either the SB or the CSB. Between 1991 and the accident no further disassembly of the engine or cylinders took place to the extent to allow for the inspection of the connecting rods. The Teledyne Industries IO-360 Overhaul Manual, current at the time of the overhaul, also provided the serviceable limit dimension for the connecting rod beam at the narrowest point; 0.625 inches. There was no indication of what service information or manuals the mechanic(s) used or had available to them at the time of the overhaul.
The total loss of engine power due to the fatigue failure of the No. 1 connecting rod. Contributing to the accident was the manufacturer’s exclusion of the accident engine (by serial number) in a revision of a service bulletin.
Source: NTSB Aviation Accident Database
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