NTSB Factual Report

On September 6, 2007, about 1800 eastern daylight time, a Piper PA-23-250, N62BA, was substantially damaged during an in-flight fire near Bernardsville, NJ. The certificated commercial pilot was not injured. Visual meteorological conditions prevailed, and no flight plan was filed. The positioning flight, which originated at Northeast Philadelphia Airport (PNE), Philadelphia, Pennsylvania, and was destined for Stewart International Airport (SWF), Newburgh, New York, was conducted under the provisions of 14 Code of Federal Regulations Part 91.

According to the pilot, about 25 minutes, and 45 miles, into the flight he noticed a slight vibration. He scanned the engine instruments and noticed a partial loss of fuel flow to the right engine. He then decided to return to PNE for a precautionary landing, and to have the problem diagnosed. The pilot continued diagnosing the problem by completing the applicable checklists. About 2 to 3 minutes later, he noticed a small streak of smoke trailing along the right engine cowling, so he elected to shut down the right engine as a precautionary measure. He then observed a flame emanating from the right side of the engine, so he pitched the nose of the airplane down, increasing the airspeed, and subsequently extinguishing the fire almost immediately. The pilot later landed uneventfully at PNE.

Examination of the right engine by a Federal Aviation Administration (FAA) inspector revealed that the number 3 cylinder was separated from the engine case, and that the right wing was substantially damaged.

Portions of the engine including the number 3 cylinder and its associated hardware; a portion of the crank case from the number 3 cylinder location; and the hold down plates for cylinder numbers 1, 2, and 4, were forwarded to the Safety Board Materials Laboratory for detailed examination. According to the Materials Laboratory Factual Report, the fracture surfaces of two of the studs used two attach the number 3 cylinder, both consistent in size with cylinder through bolts, were examined. Both fracture surfaces were relatively smooth and slightly concave across 90-percent of the fracture surface, features consistent with fatigue fractures. The other smaller diameter studs exhibited rougher fracture features with curving bands across approximately 60- to 75-percent of the fracture surfaces, features consistent with fatigue under relatively high stress.

Gray paint, similar in color to the paint on the rest of the cylinder exterior, was observed on the outboard surface of the number 3 cylinder mounting flange in areas that made contact with the hold down plates. According to the Overhaul Manual for Lycoming Direct Drive Aircraft engines, the cylinder flange should only have a 0.0005-inch maximum layer of zinc chromate primer applied. The primer should appear green with a yellowish tint, and metal should show through. The flange area in contact with the hold down plates should then be masked before painting the cylinder with a phthalate resin-type enamel.

The thickness of the cylinder flange was measured at the location where gray paint was observed, and at an adjacent area where bare metal was observed. The flanged measured 0.2567-inch in the area with the paint, and 0.2556-inch in the adjacent area of bare metal; indicating a 0.0011-inch thick layer of paint.

Further examination of the number 3 cylinder hold down plates revealed that one of the stud holes had gray paint around the hole in the nut contact area. On the opposite side of the plate, the cylinder flange contact side, the surface around the upper left stud hole and a smaller area around the adjacent stud hole were shiny and polished. All other stud holes in the submitted plates exhibited bare metal in the nut contact areas around the stud holes.

According to the operator, the right engine was last overhauled 1,055 flight hours prior to the accident flight, and had accumulated 52 flight hours since the most recent annual inspection. An FAA inspector examined the engine logbook records and found no entries stating that any of the cylinders had been removed or replaced since the last engine overhaul.

According to FAA maintenance inspection records (FAA Form 8130-3, Airworthiness Approval Tag), the cylinders installed during the overhaul were new, and had serial and cylinder class numbers stamped on them. The engine overhauler stated that new cylinders were received with a thin coat of zinc chromate, and that the engine was painted after reassembly. The failed No. 3 cylinder examined after the accident did not have serial numbers, and had paint between the cylinder flange and hold down plate.

The pilot held a commercial pilot certificate with ratings for airplane single and multiengine land, and instrument airplane. He reported 8,100 total hours of flight experience, 4,600 hours of which were in the accident airplane make and model.

NTSB Probable Cause

The failure by unidentified maintenance personnel to follow appropriate procedures when attaching the No. 3 cylinder, which was replaced subsequent to the engine overhaul and not entered in the logbook, resulting in fatigue failures of the cylinder studs.