ERA16LA123

The pilot was conducting a cross-county flight in the single-engine airplane when the engine began to run rough. Shortly thereafter, the engine experienced a partial loss of power and the pilot subsequently performed a forced landing to a golf course. During the landing, the airplane impacted trees and sustained substantial damage to the left wing. Examination of the engine revealed that two nuts were missing from the No. 3 cylinder head studs, three nuts were loose, and a third stud was fractured. The mostly-flat fracture surface of the stud exhibited features and striations consistent with fatigue, with a shear lip on one side that displayed features consistent with overstress. The fatigue fracture of the No. 3 cylinder head stud led to the loss of engine power and the loosening of several of the other nuts that secured the No. 3 cylinder head to its base.

On March 5, 2016, about 1345 eastern standard time, a Taylorcraft BL-65, N22661, was substantially damaged during a forced landing near St. Petersburg, Florida. The private pilot and a passenger were not injured. The local personal flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. The pilot reported that after flying for about 1 hour uneventfully, the airplane's engine began to run rough. Shortly thereafter, the engine experienced a 50% power reduction and the pilot subsequently performed a forced landing to a golf course. During the landing, the airplane struck trees and sustained substantial damage to the left wing, which partially separated from the fuselage. The airplane was manufactured in 1939 and was equipped with a Lycoming O-145-B2, 65-horsepower engine. Examination of the engine by a Federal Aviation Administration inspector revealed that two nuts were missing from the No. 3 cylinder head studs, three nuts were loose, and a third stud was fractured. The corresponding portion of the fractured stud was located on the cylinder cooling fins with the nut and self-looking washer still attached. The cylinder head and fractured stud were forwarded to the NTSB Materials Laboratory, Washington, DC, for further examination. Metallurgical examination of the No. 3 cylinder head revealed that the insert that was installed in the hole that contained the fractured stud had been partially pulled out and protruded above the cylinder head face. The mostly flat fracture surface of the stud contained features and striations consistent with fatigue, with a shear lip on one side that displayed features consistent with overstress. A second stud was partially pulled out of the cylinder head. The remaining studs all appeared to still be seated inside their mating cylinder head holes. Review of maintenance records revealed that airplane's most recent annual inspection was performed on May 15, 2015, about 42 hours before the accident. The engine had been operated for about 18 hours since its most recent inspection, which was performed on October 8, 2015, and included a check of all cylinder head bolts for "tightness."