Accident Overview
On April 7, 2008, at approximately 1450 central daylight time, a single-engine Piper PA-28-180 (registration N5300L) sustained substantial damage after a section of propeller blade separated during cruise flight. The aircraft subsequently made a forced landing to a wheat field near Paducah, Texas. The certified private pilot and passenger were not injured. The airplane was registered to and operated by the pilot. No flight plan was filed for the business flight, which departed Clark Field Municipal Airport (SEP) in Stephenville, Texas, around 1300, destined for Moore County Airport (DUX) in Dumas, Texas. Visual meteorological conditions prevailed for the flight conducted under 14 Code of Federal Regulations Part 91.
Examination Findings
The pilot reported that while cruising at 6,500 feet approximately 15 miles south of Childress, Texas, the propeller broke off with a "bang" followed by "extremely violent shaking as if the engine was going to fall off." He reduced power, slowed the airplane, and stalled the propeller to reduce vibrations, then declared an emergency and executed a forced landing to a field.
Post-accident examination at a salvage facility revealed that about 44 inches of one Sensenich fixed-pitch metal propeller blade had separated and was not recovered; the other blade remained intact. The top and bottom engine mounts on the right side (as viewed from the cockpit) were severed, displacing the engine down and to the right. Additionally, the lower right side of the Plexiglas windshield had pulled away from the fuselage, with some wrinkles in the surrounding fuselage area.
Further examination of the fractured propeller blade (model M76EMMS, serial number 44624) at the NTSB Materials Laboratory on April 16, 2008, showed two distinct fracture areas. One area was relatively flat, chordwise, and reflective with crack arrest positions, typical of fatigue cracking, extending through about 85% of the blade cross-section at the fracture location. Crack arrest fronts led to a crack initiation point on the camber side, 2.6 inches from the leading edge. Stripping paint from the exterior near the origin revealed small corrosion pits, with the indicated pit about 0.004 inch wide. The remaining fracture portion was jagged, matte, and slanted, indicative of final overstress fracture.
Maintenance History
A review of Sensenich's records showed that in April 1991, the accident propeller (original to the airplane) was sent to Sensenich for rework but was rejected due to being "out of material chord at the tip." It was returned to the previous owner and later reinstalled on the airplane, though no entry in the airframe logbook indicated when or by whom this was accomplished.
On June 13, 1996, the FAA issued Airworthiness Directive (AD) 69-09-03, Revision 3, for Sensenich propeller models including M76EMMS. The directive aimed to prevent propeller blade tip fatigue failure that could result in loss of control. It required removal, inspection, and rework per Sensenich Service Bulletin R-14A (dated July 28, 1995). Propellers found satisfactory were to be marked with suffix letter "K." Examination of the accident propeller revealed no "K" marking, and a review of the airframe logbook showed that the AD had not been complied with as required.
Pilot Information
The pilot held a private pilot certificate for single-engine land aircraft. His last second-class FAA medical was issued in May 2007. He reported a total of 257 flight hours, of which 219 were in the same make and model as the accident airplane.
Weather
Weather reported at Childress Municipal Airport (CDS), about 16 miles northwest of the accident site, at 1353 central daylight time: wind from 170 degrees at 6 knots, visibility 10 miles, and clear skies.