Incident Overview
On August 5, 2011, at approximately 1430 central daylight time, a Piper PA-28-180, registration N7689W, sustained substantial damage after a section of propeller blade separated in flight. The airplane was forced to land on a highway near Millsap, Texas. The private pilot and his passenger were not injured. The aircraft had departed Mineral Wells Airport (MWL) around 1415, destined for Grand Prairie Municipal Airport (GPM) in Grand Prairie, Texas. No flight plan was filed, and visual meteorological conditions prevailed for the flight conducted under 14 Code of Federal Regulations Part 91.
Pilot's Account
The pilot reported that he was leveling off at 3,400 feet mean sea level (msl) when the airplane made a "severe jerk" and began to vibrate violently. Smoke was observed coming through the firewall, and faceplates on the instrument panel began to fall off. The pilot shut down the engine by pulling the mixture control. After the engine stopped, a large section of a propeller blade was observed missing. The pilot trimmed the airplane for best glide speed and landed on a road. During the landing roll, the right wing struck a road sign.
Damage and Examination
According to the pilot, an 18-inch long section of propeller blade was missing, and the engine had broken loose from several motor mounts. Secondary damage to the engine and components was also reported. Metallurgical examination of the remaining blade section revealed striations on the fracture surface consistent with crack initiation and propagation by high cycle fatigue. At least three crack arrest marks were observed, consistent with the stopping and starting of cyclic stresses.
Maintenance and Airworthiness Directive
Examination of maintenance records showed that the Sensenich propeller (part number 76EM8-0-60, serial number 13700K) had been overhauled on July 30, 2004, and reinstalled on the Lycoming O-360-A3A engine. The last 100-hour inspection was completed on October 1, 2010, at a total time of 165.73 hours since overhaul. The Federal Aviation Administration (FAA) had issued Airworthiness Directive (AD) 69-09-03 R3 on May 15, 1996, applicable to Sensenich 76EM8 propellers mounted to Lycoming O-360-A3A engines. The AD aimed to prevent propeller blade tip fatigue failure, which could result in loss of control. It required factory inspection and reconditioning for propellers with 500 hours or more of flight time. Propellers inspected or reworked per the AD were to be identified with the suffix letter "K" after the serial number, which was present on the accident propeller. The AD also prohibited continuous operation between 2150 and 2350 RPM and required marking the tachometer with a red arc in that range. The pilot stated he was aware of the AD and had complied with the RPM restriction.