Accident Summary
On September 1, 2012, at about 1130 mountain daylight time, a TL Ultralight SRO Stingsport airplane, registration N898N, conducted a forced landing after two of its three propeller blades separated in flight near Longmont, Colorado. The airplane sustained substantial damage. The sport pilot and the designated pilot examiner (DPE) on board were not injured.
Flight and Aircraft Information
The flight was conducted as an instructional flight under 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed. The flight originated from Erie Municipal Airport (KEIK), Erie, Colorado, at 1100. The airplane was a two-place, high wing, fixed gear light sport airplane manufactured in 2006. It was powered by a Bombardier Rotax engine and equipped with a three-bladed WoodComp wooden propeller. An airworthiness certificate was issued for N889N on March 10, 2006.
Pilot and Examiner Actions
The DPE stated that while the pilot was conducting a steep turn demonstration at 2,500 feet above ground level, the engine began vibrating violently. The pilot aborted the maneuver and retarded the throttle to idle, after which the engine experienced a total loss of power. The pilot made an emergency landing in a nearby field. After landing, the pilot and DPE noticed that two of the three propeller blades had separated from the propeller hub.
Propeller Inspection History
Visual inspections of the propeller and propeller hub, and bolt torque checks, were performed per the manufacturer's instructions on August 1, 2009 (total time 158.4 hours), August 3, 2009 (total time 361.2 hours), August 12, 2010 (total time 680.9 hours), and September 1, 2011 (total time 924.8 hours). According to WoodComp, the propeller inspections were required at 150-hour intervals.
Wreckage and Examination
The airplane came to rest upright in a field. The engine mounts and firewall were bent during the forced landing. The remaining propeller blade and all three propeller sleeves were examined by the NTSB Materials Laboratory. Blades and sleeves were labeled A, B, and C. Blade A consisted of an entire blade sleeve with a small amount of fractured wood inside; a tan powdery substance matching the wood propeller was noted. Progressive cracks were evident between the blade and the metal sleeve. Blade B consisted of an entire blade sleeve with a section of wood attached and extending out; cracks were present in the wood at the interface with the sleeve. Blade C consisted of an entire blade sleeve and entire wood blade, with kinked fibers in the composite layer and crack features at the blade root near the metal sleeve.