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On April 30, 2000, about 1635 Eastern Daylight Time, a Beech 36, N28JP, was substantially damaged during a forced landing to a field in Nassawadox, Virginia. The certificated commercial pilot and three passengers were seriously injured. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight conducted under 14 CFR Part 91.
The pilot described the events surrounding the accident in a written statement. He said:
"On April 30, 2000, I was piloting a Beech Bonanza A36 aircraft of which I am the owner. Conditions were VMC and I had flight following for the flight originating at the Dare County Regional Airport (MQI) located in Manteo, North Carolina, destined for Delaware Airpark Airport (33N), Dover, Delaware. The tanks were topped off prior to departure from MQI."
"We were in-flight for approximately 40-50 minutes and flying along the coast over Kitty Hawk when I felt the engine began to run rough North of the Chesapeake Bay. All of my engine instruments were observed by me to be in the green at this time, including oil pressure. I richened and leaned the mixture, but there was no improvement in engine performance."
"The aircraft then began loosing altitude and I applied additional power. I radioed Norfolk to declare an emergency. I believed Accomack Airport to be approximately 5 miles away and straight ahead. I raised my airspeed to maintain altitude but continued to loose altitude nonetheless. I then heard a loud "bang" and observed oil on the windshield. The prop began windmilling and I made a shallow left turn to the west in search of an appropriate place to land. I shut the main fuel and made a shallow right turn to parallel highway 13. I eventually landed in a soft field near the highway."
A Safety Board investigator interviewed the pilot after the accident. He was asked to describe his procedure for leaning the mixture, and explained that he always leans the mixture to 1,400 degrees on the EGT. He estimated this figure corresponded with a fuel burn rate of 16 gallons per hour.
In a subsequent telephone interview, the pilot reported that during the accident flight he remained at a power setting of 25 inches of manifold pressure and 2500 RPMs. He also stated that as he flew "over the Peninsula" he noticed that the engine had developed a slight roughness, and the sound began to "hum lower." About 8 miles from the Accomack County Airport, the oil pressure decreased and the engine "was getting very rough." The pilot heard a "pop," and the engine lost all power. He then performed a forced landing to a field.
In a written statement, a passenger seated in the right front seat reported:
"We took off from Manteo and climbed to 6,500 feet. I noticed we started loosing oil pressure and I mentioned it to the captain. We started looking for a place to land. We tried to make Melfa and couldn't do it. We picked the best field to do it."
A witness reported hearing the airplane "spitting" and "sputtering." Smoke was observed coming from the left side of the airplane as it "broke to the right," and went down in a field.
A second witness reported hearing a "cluttering or clicking" noise coming from the airplane, as it banked to the left. The airplane then "pancaked," hit the ground, and came to an abrupt stop.
A third witness stated the engine noise "didn't sound right," and observed a brief trail of smoke from the airplane. The airplane then banked to the left, straightened, and started to loose altitude. The engine noise "got worse" as the airplane descended.
The pilot held a commercial pilot certificate with ratings for instrument airplane and airplane single engine land. He reported 4,500 hours of total flight experience on his most recent Federal Aviation Administration (FAA) second class medical certificate, which was issued on January 5, 2000.
According to the pilot's logbook, during the 12 months prior to the accident, he flew 93 hours in the make and model of the accident airplane. The pilot reported 2,000 total flight hours in the make and model of the accident airplane, on the NTSB Pilot/Operator Aircraft Accident Report.
The airplane received an annual inspection on October 28, 1999, about 44 flight hours prior to the accident flight.
Examination of the airplane by an FAA inspector revealed that all major components of the airplane were accounted for at the scene. The airplane came to rest on a heading of 350 degrees, and virtually no ground scars were observed leading to the wreckage. The surrounding vegetation was not damaged, except for a 4-foot path leading to the wreckage that was "coated with oil."
The airplane, aft of the engine mounts exhibited upward compression, consistent with a "near vertical descent." The underside of the airplane was covered with oil, and evidence of an oil fire was observed in the engine compartment. The landing gear and flaps were both retracted.
Examination of the engine revealed a fist-size hole on the top of the crankcase, and the #5 connecting rod was pushed out of the case. No evidence of oil was observed in the crankcase. The #5 and #6 cylinder lower rocker box cover screws appeared to be "finger tight." Oil could be traced from the rocker box to the forward exhaust stack.
TESTS AND RESEARCH
The engine was removed from the accident site and examined in a hangar in Hagerstown, Maryland, on May 5, 2000. Present for the examination was an FAA inspector, a representative of the engine manufacturer, and a representative of the airplane manufacturer.
The #2 cylinder was removed from the engine case and metallic granules were observed embedded in its interior. When the #2 piston was removed, a hole was observed on the side of the piston, at the 6 o'clock position, which extended through the piston from the side to the interior. The top compression piston ring was intact; however, the second compression piston ring and the oil control ring were broken. A portion of the piston beneath the oil control ring was broken, and the forward end of the piston pin was chipped.
The #1, #3, and #4 cylinders were removed from the engine case, and their corresponding pistons were removed from the cylinders. No abnormalities were observed in the pistons or their cylinders. Removal of the #5 and #6 cylinders and their pistons was not possible due to severe damage to the cylinder skirts. However, the pistons moved freely inside the cylinders, and no abnormalities were observed.
The engine case was split, the crankshaft was removed, and it was noted that the #5 and #6 connecting rods had separated from the crankshaft. The #5 and #6 rod journals were blackened, and their bearings completely disintegrated.
The #1, #2, #3, and #4 connecting rods remained attached to the crankshaft at their journals. The #1 connecting rod rotated normally around its rod journal, which displayed light scoring, and its bearing did not reveal any abnormalities. The #2 connecting rod was difficult to rotate, and was a whitish gray color at the crankshaft end. The #2 rod journal was blackened and heavily scored. The #3 and #4 connecting rods also displayed a whitish gray color and their bearings were almost completely disintegrated. Their connecting rod bolts were secured; however, the #3 and #4 connecting rods were loose on their journals. The #3 and #4 rod journals were scored and blackened.
The engine driven fuel pump, manifold valve, fuel injector nozzles, and fuel metering unit were examined at Teledyne Continental Motors on September 12, 2000, under the supervision of a Safety Board investigator. An initial attempt to flow check the fuel pump was unsuccessful due to a clogged fuel vapor return jet. The return jet was removed and reinstalled, and the fuel pump flowed normally. It was noted that the fuel pump fittings were not capped during shipping. A flow check of the fuel injector (FI) nozzles revealed a clogged #2 fuel nozzle. Fuel flow was ceased and reapplied and the nozzle flowed normally. Contamination present in the nozzle orifice was forced out during the second attempt to flow check the nozzle. It was also noted that the FI nozzles were not capped during shipping. Examination of the manifold valve and fuel metering unit revealed no discrepancies.
The #2 cylinder assembly, piston, and connecting rod were examined at the National Transportation Safety Board Materials Laboratory, Washington, D.C., on July 30, 2000. According to the Materials Laboratory Factual Report:
"Optical examinations showed severe deterioration of the piston including erosion of the head crown and scoring of the skirt. The edge of the piston was completely missing from the combustion surface to the first compression ring and around more than half of the perimeter. In the missing areas the surfaces had a roughened eroded appearance. The piston skirt was heavily scored completely around the cylinder and some of the rings were stuck in their prospective groves. Heavy particulate material was partially fused to combustion surfaces of the piston crown and the cylinder head. The material appeared to be from the piston...The damage to the piston and the combustion surface deposits are indicative of detonation in the cylinder."
Detonation was described in the FAA publication AC65-12A as "the instantaneous and explosive burning of the fuel/air mixture. The explosive burning during detonation results in an extremely rapid pressure rise. This rapid pressure rise and the high instantaneous temperature, combined with the high turbulence generated, cause a 'scrubbing' action on the cylinder and the piston. This can burn a hole completely through the piston."
The Advisory Circular further stated, "...the presence of severe detonation during its operation is indicated by dished piston heads, collapsed valve heads, broken ring lands, or eroded portions of valves, pistons, or cylinder heads."
Factors affecting detonation were described as design, cylinder cooling, magneto timing, mixture distribution, and carburetor settings.