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On January 25, 2006, approximately 1900 central standard time, a single-engine Cessna 175 airplane, N6612E, registered to and operated by a private individual, was substantially damaged following a hard landing at the Lindsay Municipal Airport (1K2), near Lindsay, Oklahoma. The private pilot, sole occupant of the airplane, was not injured. Night visual meteorological conditions prevailed, and a flight plan was not filed for the 14 Code of Federal Regulations Part 91 personal flight. The local flight originated from the Shawnee Regional Airport (SNL), near Shawnee, Oklahoma, approximately 1815.
The 156-hour pilot reported in a written statement that while on a full-flap approach to runway 01, a 3,000- feet long by 40-feet wide asphalt runway, he allowed the airplane's airspeed to decrease while flaring too high, resulting in a hard landing.
The pilot held an airplane single-engine land rating. His most recent Federal Aviation Administration (FAA) third-class medical certificate was issued on September 30, 2004, without limitations or waivers.
The 1959 model, serial number 56112, was a high-wing, all-metal airplane, configured for a maximum of four occupants, with a fixed tricycle landing gear. The airplane was powered by a 1966 Continental IO-360-C engine, serial number F50482-6-C, rated at 210 horsepower, driving a McCauley D2A34C-76C propeller. According to the owner, the airframe total time was 2,756.1 hours, and the total time on the engine was 2,105 hours, with 801 hours since last overhaul. The airplane's last annual inspection was performed on July 22, 2005.
At 1906, the automated weather observing system (AWOS) at the Pauls Valley Municipal Airport (PVJ), near Pauls Valley, Oklahoma, located approximately 20 nautical miles southeast of the accident site, reported wind from 150 degrees at 4 knots, visibility 10 statute miles, sky clear, temperature 61 degrees Fahrenheit, dew point 25 degrees Fahrenheit, and barometric pressure of 30.43 inches of Mercury. The NTSB IIC calculated the density altitude to be 927 feet.
WRECKAGE AND IMPACT INFORMATION
Examination of the airplane by a Federal Aviation Administration (FAA) inspector, who responded to the accident site, revealed the presence of a crack that propagated from the left upper support-mount bracket bolt hole (part number 0513132-11). There was also a red substance at the fracture, which was consistent with corrosion. The inspector added that the right upper support-mount bracket attachment rivets had separated from the airframe stringer assembly, and the upper portion of the firewall was separated from the airframe, resulting in the engine been tilted approximately 30 degrees downward.
TESTS AND RESEARCH
The upper engine mount brackets were sent on February 3, 2006, for further examination to the NTSB Materials Laboratory, in Washington, D.C.
Cessna document drawing 0513132 of the stringer assembly and the engine mount bracket were examined. Details of the examination from the NTSB laboratory revealed that the engine mount brackets fractured due to metal fatigue. The examination also revealed that the metal content of the brackets did not contain the amount of chromium or silicon that were constituent elements of the specified material, which was SAE 4130. The hardness of the brackets also indicated that the tensile strength was approximately 40 percent below the specified strength.
The FAA issued Advisory Circular 43-16A, titled Aviation Maintenance Alert Bulletin number 334, in May 2006 for Cessna series 172, R172, and 175 model airplanes pertaining to a cracked engine mount attach bracket. The alert was taken from service difficulty report (SDR) 2006FA0000244 that was issued on February 10, 2006. A month later, Aviation Maintenance Alert Bulletin number 335, which was issued in June 2006, included the 172 series 47747 to 49544 and 175 series 55001 to 57119 airplanes. The bulletin noted that SDR data base records listed 17 entries for that particular part number (0513132-11) under ATA code 5313 (fuselage longerons/stringers).
By using ATA code 7120 (powerplant mounts), the data base recorded an additional 13 SDRs for broken/cracked attach brackets on 172/175 airplanes .
Currently, Cessna Aircraft is working on a service information document to address mandatory inspection procedures for the model 175 (schedule for release in the fall of 2006). The document will include 172 models from 28000 to 72884, F172 model 0001 to 1009, all series of the P172 and FP 172 models, R172 models from 2000 to 3199, and FR172 models from 00001 to 00655.
The wreckage components were released to the owner's representative on February 3, 2005.