DFW08LA094 · Piper PA-28-180

The private pilot/owner and the passenger were on a cross country flight at an altitude of 6,500 feet when a section of propeller blade broke off and the airplane began to shake violently. The pilot reduced power, slowed the airplane and stalled the propeller, which reduced the vibrations. He then declared an emergency and made a forced landing to a field. Examination of the airplane revealed that approximately 44-inches of one of the Sensenich fixed-pitch (all metal) propeller blades had separated and was not recovered. The other blade was intact. The top and bottom engine mounts on the right side (as viewed from the cockpit) were severed and the engine was displaced down and to the right. A materials examination of the propeller's fractured surface revealed fatigue cracking through approximately 85 percent of the blade and corrosion pitting at the initiation point of the failure. The remaining portion of the fracture was more jagged, had a matte appearance, and was oriented at a slant angle, which was indicative of a final overstress fracture region. A review of Sensenich's records revealed that in April 1991, this propeller (which was original to the airplane) was sent to Sensenich to be reworked; however, it was rejected due to the fact that it was "out of material chord at the tip." The propeller was returned, and at some point was placed back on the airplane. However, there was no logged entry in the airframe logbook that indicated when this was accomplished or by whom. On June 13, 1996, the FAA issued Airworthiness Directive (AD) 69-09-03, Revision 3, titled, Sensenich Propeller Manufacturing Company Incorporated models M76EMM, M76EMMS, 76EM8, and 76EM8S metal propellers. The directive was issued, "To prevent propeller blade tip fatigue failure, which can result in loss of control of the aircraft..." As a result, this particular propeller was to be removed, inspected, and reworked in accordance with Senseinich Propeller Service Bulletin (SB) number R-14A, dated July 28, 1995. Those propellers that had been inspected in accordance to the Service Bulletin and found satisfactory were to be marked with the suffix letter "K." Examination of the accident propeller revealed there was no "K" marking. In addition, a review of the logbooks revealed that the AD had not been complied with as required per Federal Aviation Regulations.

Verbatim NTSB analysis and probable cause from the NTSB dataset