Accident Overview
On October 12, 2012, at about 1835 eastern daylight time, a Piper PA-28-140, registration N15037, operated by Ace Pilot Training Inc., was substantially damaged during a forced landing to a corn field following a partial loss of engine power. The aircraft had just departed from Lehigh Valley International Airport (ABE), Allentown, Pennsylvania. The certified flight instructor (CFI) and private pilot were not injured. The instructional flight was conducted under 14 Code of Federal Regulations Part 91 in visual meteorological conditions. No flight plan was filed.
Flight Events
According to the CFI, the airplane was fueled to 36 gallons before the flight. Engine start-up, taxi, and run-up were normal. During departure from runway 31, at about 200 feet above ground level, the CFI noticed the throttle lever did not appear to be completely forward. He and the private pilot pushed the throttle lever full forward, meeting resistance, after which the engine began sputtering. The CFI applied carburetor heat, but the engine continued to sputter. He elected to land in a corn field. During the landing, the engine firewall and right aileron were substantially damaged.
Post-Accident Examination
A Federal Aviation Administration (FAA) inspector examined the wreckage and found that the No. 2 top sparkplug, No. 3 bottom sparkplug, and No. 3 top sparkplug were fouled. In a subsequent test run, the engine lost all power whenever the right magneto was selected. Both magnetos were retained and forwarded to the NTSB Materials Laboratory.
Laboratory examination of the right magneto revealed that seven teeth from its drive gear were fractured and exhibited single-sided bending fatigue, consistent with applied force in one direction over time. Examination of the left magneto found a loose drive gear with teeth worn along the top corner. The drive gear had not been fully seated on the drive shaft and was removed by hand. Additionally, the point cam was not fully installed and seated in the bottom of its slot and exhibited a wear scar where the cam contacted the points. The mis-installed cam prevented full seating of the drive gear onto the drive shaft. When the distributor cap was installed, the top corner of the drive gear contacted the distributor housing. The wobbling action of the drive gear during operation resulted in wear of the gear teeth, though the mis-installation did not appear to prevent the left magneto from operating in its current condition.
Maintenance History
The airplane was manufactured in 1972 and equipped with a Lycoming O-320-E3D, 150-horsepower engine. According to maintenance records and an FAA inspector, the most recent annual inspection was completed on August 22, 2012. The engine's most recent overhaul was completed on June 27, 2005. At the time of the accident, the engine had accumulated approximately 72 hours since the annual inspection and 2,300 hours since overhaul. The FAA inspector noted that the accident magnetos (Unison [Slick] model 4370 right, and model 4371 left) were installed at overhaul and had not been replaced or serviced during the time since overhaul. When the inspector attempted to disassemble the magnetos, he had to remove inspector's lacquer (yellow paint) from screw holes, consistent with the magnetos never having been disassembled for inspection since overhaul. The engine manufacturer recommended overhauling the engine every 2,000 hours or 12 years, which would have included replacing the magnetos with new or overhauled units. Additionally, Slick service bulletin SB-308A recommended inspecting the magnetos every 500 hours.