BFO94LA038

The flight was cruising at 7500' when the engine started to run rough 12.2 nautical miles from Norfolk airport. The pilot stated that he did not change the propeller setting until he was overhead the airport. Thereafter there was a loud explosion and the oil access door blew open and pieces of the engine exited the airplane. During the forced landing on runway 23 the airplane touched down on the grassy area. Examination revealed the no. 2 cylinder assembly, piston and connecting rod separated from the crankcase at the cylinder hold-down stud area. For metallurgical examination the hold- down studs along with the crankcase were sent to the NTSB lab in Washington, DC. The examination disclosed fatigue cracks and there was evidence of welding through the crankcase. The welding areas were softer than the areas that were not welded.

On Monday, February 7, 1994, at 1600 eastern standard time, a Piper PA-32R-300, N38780, collided with the ground following a power-off forced landing at Norfolk International Airport, Norfolk, Virginia. The certificated flight instructor, and his five passengers were not injured while the airplane sustained substantial damage. The airplane was being operated under 14 CFR 91. The flight originated in Greenville, North Carolina. The intended destination was Hartford, Connecticut. Visual meteorological conditions prevailed and a flight plan was not filed.

The pilot stated that he and his five passengers were at a cruising altitude of 7500 feet MSL when, "the engine changed vibration and ran somewhat rough." He stated that he took the controls from the student and declared an emergency with Norfolk Approach as he was 12.2 nautical miles from Norfolk Airport. The pilot stated that he advised Norfolk Approach that he would try to maintain his current altitude and try to correct the problem.

The pilot stated that enroute to the airport he did not change any of the power settings until he was directly overhead the airport. He stated that he increased the propeller rpm slowly, and shortly thereafter he heard a loud explosion coming from under the left side of the engine cowling. He stated that the oil access door blew open, and pieces of the engine exited the aircraft. The pilot stated that he shut the engine down by turning off the magnetos and made a forced landing at Norfolk Airport. During the forced landing on runway 23, the airplane touched down west of the runway in a grassy area.

The airplane was examined at the accident site by the FAA. The examination revealed oil on the windshield of the airplane, and the number 2 cylinder along with its respective piston and connecting rod had exited the engine through the engine cowling. The engine was removed from the airplane and shipped to Piedmont Aviation Services Inc., of Winston-Salem, North Carolina, for examination. The examination confirmed the number 2 cylinder was missing from the crankcase and the attaching studs and thru bolts were fractured. The breakaway torque was checked on all cylinder studs and thru bolts which were not affected by the cylinder separation. The values for each are listed on the attached two tables.

The remaining hold down stud bolts along with the crankcase were sent to the NTSB Lab in Washington, DC, for metallurgical examination. The examination revealed that the separation of the six hold down studs and two through bolts for the number two cylinder were the result of fatigue cracks that emanated along multiple sites at the root of the threads. Metallographic section through the pad for one of the hold down studs for the number 2 cylinder revealed that extensive weld repair had been performed through the entire thickness of the case at this location. Hardness measurements on the section cut from the engine case showed that the welded areas were much softer than the areas that were not welded.

The investigation revealed that the engine had over 3834 hours of total time, including 343 hours since major overhaul. The last annual inspection was completed on September 20, 1993, and the airplane had accumulated over 160 hours since the last inspection.