Accident Details
On June 1, 2013, at approximately 0830 eastern daylight time, a Maule M-4-220C, registration N40337, operated by a private individual, was substantially damaged during a forced landing. The airplane had just departed Farmers Pride Airport (9N7) in Fredericksburg, Pennsylvania, and was destined for Baublitz Commercial Airport (9W8) in Brogue, Pennsylvania. The pilot, an airline transport pilot, reported that after climbing to 2,500 feet mean sea level, the engine began to vibrate and lose power. White smoke filled the cabin. The pilot shut down the engine and executed a forced landing to a soybean field. During the landing roll, the airplane entered a wheat field and nosed over, resulting in substantial damage to the fuselage and vertical stabilizer. The pilot sustained minor injuries; the passenger was not injured. Visual meteorological conditions prevailed and no flight plan had been filed. The flight was conducted under 14 CFR Part 91.
Aircraft and Engine Examination
The airplane, manufactured in 1972, was equipped with a Franklin 6A-350-C1 220-horsepower engine. An initial examination by a Federal Aviation Administration inspector revealed that the No. 4 cylinder head was partially separated from the cylinder barrel, the No. 4 piston was fragmented, and the No. 4 piston pin was fractured. The No. 4 cylinder, connecting rod, fractured piston pin, and piston fragment were sent to the NTSB Materials Laboratory for further examination.
An NTSB metallurgist found that the No. 4 piston pin was circumferentially fractured near its midpoint. The connecting rod was not fractured, but the piston pin bearing in the small end was fractured and damaged, with the separation surface completely obliterated. The piston pin fracture location corresponded to the separation of the piston pin bearing in the connecting rod. Scanning electron microscope examination of the piston pin fracture revealed striations consistent with fatigue propagation that initiated at the pin outer diameter.
The No. 4 piston fragment, estimated to comprise about one-third of the piston crown, was severely battered. Almost all fracture surfaces were obliterated by mechanical damage; the few undamaged areas appeared typical of overstress separations. The No. 4 cylinder was fractured through its bore with overstress features on both the aluminum cylinder and steel liner, with no indications of preexisting cracking.
Maintenance History
According to maintenance records, the airplane and engine had been operated for about 50 hours since its most recent annual inspection, performed on June 27, 2012. The engine had accumulated about 1,400 total hours since new. The No. 4 cylinder was overhauled during June 1990, about 560 hours prior to the accident, and was also removed, reconditioned, and reinstalled during April 2009, about 165 hours prior to the accident.