Unadilla, GA, USA
N780SR
Ryan ST-3KR
The pilot was flying the recently-acquired airplane on a cross-country flight. During the descent for landing, the engine shook violently followed by the wooden propeller blades separating at the hub. The pilot landed the airplane in a field, resulting in substantial damage. The previous owner had the propeller replaced with an older one prior to delivery of the airplane, stating that he did not want the new owner to "ding up the expensive new prop." Examination of the remaining hub and attachment bolt revealed evidence of fatigue failure due to excessive looseness of the attachment bolts. The mechanic who replaced the propeller did not adequately document its replacement. Reportedly, the propeller that failed had been in storage for 30 years, and showed evidence of gray staining deep into the wood, indicative of significant moisture penetration over an extended period of time.
On October 20, 2007, at approximately 1000 eastern daylight time, a Ryan ST-3KR, N780SR, was substantially damaged during a forced landing near Unadilla, Georgia, after the propeller separated from the airplane. The certificated commercial pilot was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the flight, which departed Cook County Airport (15J), Adel, Georgia, destined for Perry-Houston County Airport (PXE), Perry, Georgia. The personal flight was conducted under the provisions of 14 Code of Federal Regulations (CFR) Part 91. According to the pilot, he had recently purchased the airplane in Winter Garden, Florida, and had partially completed a multiple leg trip, which would terminate in Nashville, Tennessee. At approximately 0845 on the day of the accident, the pilot started the airplane and after completing his run-up, departed 15J. Upon reaching his cruising altitude of 2,500 feet mean sea level (msl), he turned directly for PXE. The flight was uneventful for the first 75 minutes of flight. At approximately 0955, the pilot initiated a descent to 1,500 feet msl in preparation for landing at PXE. Approximately 5 minutes later the airplane began to shake "violently," and after approximately 10 seconds, the propeller "flew apart." The pilot then reduced power to idle and shut off the mixture control in order to keep the engine from separating from the airplane. He then determined that the best available place to land was an open hay field that was off to his left side, and began to maneuver for landing. Just prior to landing, a "large amount" of oil was released from the engine area that covered the pilot. After touching down in the field, the pilot applied heavy braking. As the airplane approached a road with a built-up shoulder, the pilot applied full right brake and the airplane turned to the right and stopped. The recorded weather at Robins Air Force Base (WRB), Warner Robins, Georgia, located 24 miles northeast of the accident site, at 0955, included winds from 330 degrees at 5 knots, 10 statute miles visibility, clear skies, temperature 17 degrees Celsius (C), dew point 13 degrees C, and an altimeter setting of 30.05 inches of mercury. According to FAA records, the pilot held a commercial pilot certificate with ratings for airplane single-engine land and airplane multi-engine land. His most recent FAA third-class medical certificate was issued on May 11, 2007. He reported 4,100 total hours of flight experience. Examination of the wreckage by a Federal Aviation Administration (FAA) inspector revealed that the propeller mounting bolts were damaged, and that only a small amount of material from the wooden propeller remained attached to the propeller hub. The engine had partially separated from the firewall, and the firewall was damaged. The engine's lubrication and fuel system hoses were damaged, and the landing gear and fuselage both were twisted. According to both FAA and maintenance records, the airplane was manufactured in 1942. The airplane's most recent annual inspection was completed on August 5, 2007. At the time of the inspection, the airplane had accrued 3,457.2 total hours of operation, and the engine had accrued 380 hours of operation since its last overhaul. Portions of the wooden propeller and hub were sent to the National Transportation Safety Board Materials Laboratory for examination. According to the Materials Laboratory Factual Report, "the four attachment holes...were blackened and charred, [consistent with] significant friction between them and their attachment bolts...and therefore the propeller [was] loose." There was also "gray staining that had penetrated deep into the grain of the wood...normally associated with the ingress of moisture over a significant period of time." The fracture surface of the mounting bolt contained a zone area typical of fatigue, whereas the other zone was typical of overload. An FAA inspector contacted the mechanic who had worked on the airplane. He stated that he had installed "a different propeller and hub assembly" at the previous owner's request "so that [the new owner] would not ding up the expensive good prop." The mechanic added that "the propeller was supplied with the hub already installed and that all he had to do was install the hub and propeller on the crankshaft and torque the barrel nut to 250 foot pounds with an 8-foot breaker bar." The mechanic said he did not make any logbook entry and did not have any other installation documentation other than a repair invoice. The following was written on that repair invoice: "Removed newer prop. Installed original prop owner furnished. Hub was installed and safetyed (sic). I installed master nut and torqued to specs. Aircraft was flown for two hours at our field before leaving with new owner." The following are excerpts taken from the airframe logbook: 11/1/84, 3186.5, Replace propeller with new Sensenich 5/12/86, 3236.5, Exchange Famlin propeller for Sensenich propeller SN #AA5939 1/1/87, Removed and replaced prop 3/27/99, Installed (unreadable) prop, TQW nut to proper spec The propeller that failed had been in storage for approximately 30 years.
The improper propeller installation by the mechanic.
Source: NTSB Aviation Accident Database
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