Flight Details
On July 15, 2012, at 1400 eastern daylight time, a Socata TB 10, registration N189TB, experienced a partial propeller blade separation after departing from runway 23 at North Central State Airport (SFZ), Pawtucket, Rhode Island. The aircraft was on a local instructional flight under visual meteorological conditions, and no flight plan was filed. The private pilot was at the controls under the supervision of a certified flight instructor (CFI). As the airplane climbed to about 800 feet, the occupants heard a loud noise resembling a shotgun blast, followed by severe vibrations. The CFI assumed control, reduced power, and initiated a 180-degree turn to land on runway 33. He also pulled the mixture to further reduce engine power. The aircraft landed without incident, and neither the pilot nor the CFI were injured. The airplane itself was not damaged. The CFI reported no oil on the windscreen or abnormal engine indications during the event, and vibrations continued until touchdown and the propeller stopped windmilling.
Examination of Propeller Blade
Post-incident inspection revealed that approximately 3.5 inches of the tip of one propeller blade had separated. The remaining blade section was sent to the NTSB Materials Laboratory for analysis. Visual examination showed that 80 percent of the fracture surface was relatively flat with a reflective luster, characteristic of fatigue crack propagation. The remaining 20 percent had an uneven, rough matte surface consistent with an overstress fracture. Microscopic inspection of the fatigue regions did not identify an exact origin. Additionally, the blade's cross-sectional profile near the general location of the origin differed from the expected profile. Scanning electron microscope imaging revealed markings indicative of mechanical abrasion on that surface. X-ray examination confirmed the blade's material composition as type AA2025 aluminum alloy, and hardness and conductivity testing yielded measurements consistent with the specified material.
Propeller Maintenance History
According to propeller logbook entries, the propeller blades underwent a major overhaul on February 18, 2009, following a propeller strike. The propeller was reinstalled on the aircraft on March 3, 2009, at a tachometer time of 5,007 hours. A subsequent logbook entry on April 27, 2011, at tachometer time 5,449 hours stated, "reinstalled propeller assembly after repair by Sensenich Propeller." The reason for this repair was not documented in the logbook, and no corresponding entry was found in the airframe logbook. The most recent annual inspection of the propeller was completed on January 18, 2012, at tachometer time 5,677 hours. At the time of the incident, the tachometer read 5,860 hours, indicating 669 hours since the last overhaul. Both propeller blades were manufactured by Hartzell Propellers on March 14, 1980. According to Hartzell, there is no life limit for these blades as long as they pass required overhaul inspections.