GENESEO, IL, USA
N92LL
DOTSON SEABIRD
Witnesses reported seeing the airplane about 20 minutes after takeoff traveling south from the airport at about 1000 feet AGL. The nose of the airplane pitched down, and then it came back level for about 2 seconds. Then the nose pitched down again and the airplane entered a steep, left spiral. Witnesses reported hearing the engine sputter and finally quit. The airplane impacted the ground in about a 70-degree nose-down attitude. Both 5-gallon plastic fuel tanks were ruptured during impact. There was evidence of fuel on the ground at the wreckage site. The flight controls and engine exhibited continuity. The cylinders had compression and ignition. Power was supplied to the starter with the spark plugs disconnected. The engine turned over normally. The electric boost pump operated and delivered fuel to the carburetors. The engine-driven impulse fuel pump did not supply fuel to the carburetors. The one-way check valve attached to the hose of the impulse fuel pump was examined and determined that it was blocked due to corrosion. When the impulse pump was tested without the one way check valve attached, the pump worked normally. The electric boost pump switch was found in the off position.
History of Flight On May 30, 1996, at 0930 central daylight time, an experimental Seabird, N92LL, was destroyed when it impacted the ground while in a stall/spin. The private pilot received fatal injuries. The 14 CFR 91 flight departed Gen-Air Park Airport, Geneseo, Illinois, on a local flight. Visual meteorological conditions prevailed and no flight plan was filed. A witness reported seeing the airplane depart runway 9 at Gen-Air Park about twenty minutes prior to the accident. It was not determined if the pilot remained in the airport traffic pattern, or flew elsewhere between the time of takeoff and the time of the accident. Witnesses reported seeing the airplane flying southbound from the airport toward Route 6. The altitude was described at about 1000 above ground level. A witness reported that the airplane was going straight, and then the nose of the airplane pitched down. The nose came back to level for about 2 seconds. Then the nose pitched straight down again and the airplane started a left hand, spiraling descent. The first revolution was slow, but the second and third turn were faster and tighter. The airplane impacted the ground in about a 70 degrees nose down attitude. Witnesses at a nearby golf course reported that the engine sounded normal at first. Then they heard the engine sputtering and finally stopping. They reported that the airplane was in a steep spiral and that no attempt was made to recover. Personnel Information The pilot was a 71 year old male, private pilot. He had a valid third class medical certificate and had a current biennial light review. He had flown 963 total flight hours. He had logged 39 hours of flight time in the accident aircraft. He had flown 11 hours in the accident airplane in the last 90 days and 6 hours in the last 30 days Aircraft Information The airplane was an experimental Seabird, serial number LD101. The Special Airworthiness Certificate for the amphibian airplane was issued on August 20, 1995. The total time on the airplane on the day of the accident was 39.4 hours. Wreckage and Impact Damage The airplane impacted the ground in an open field about one half mile southwest of the Gen-Air Park Airport. The impact angle was about 70 degrees nose down. The nose wheel landing gear was buried a foot and a half in the ground. The wings had leading edge crush damage. The engine and pusher mounted propeller, which were above and aft of the wing spar, crushed forward and on top of the cabin. Witnesses who arrived at the scene soon after the occurrence reported seeing and smelling fuel. The two five gallon clear plastic jugs used as fuel tanks were ruptured during impact. Fuel was found in the fuel filters and carburetor bowls. The inspection of the airplane revealed that the flight controls exhibited continuity. The propeller was not damaged during impact and all three blades were intact. The inspection of the engine revealed that the engine had continuity. All cylinders had compression and all the spark plugs had ignition. Power was supplied to the starter but with the spark plugs disconnected. The engine turned over normally as during an engine start. When the boost pump switch was engaged, the electric boost pump delivered fuel from the left fuel tank through the impulse fuel pump to the carburetors. The fuel line that went from the right fuel tank to the impulse fuel pump did not deliver fuel to the carburetors. The impulse fuel pump was examined. The fuel pump was originally designed with one fuel intake line from the fuel tank. The pilot/builder had modified the pump. He had drilled a hole in the fuel pump to accommodate a second fuel line that received fuel from the electric boost pump. A pilot familiar with the airplane reported that the pilot/builder used the manual primer and electrical boost pump during starts. He reported that during flight the electric boost pump was in the off position. During the examination of the wreckage, the boost pump was found in the off position. The electric boost pump's fuel line came from the left fuel tank. The impulse pump's fuel line came from the right fuel tank. Both fuel lines had one way check valves and filters attached to the end of the fuel lines where the fuel was picked up. The check valve that was attached to the hose that supplied fuel to the impulse fuel pump was examined. It was determined that the check valve was blocked. The metal ball inside the check valve was stuck and would not allow air or fluids to pass through the check valve. The check valve was cut in two. The inspection revealed corrosion on the barrel of the check valve and on the ball where it had attached to the side of the barrel. Medical and Pathological Information The autopsy was performed at the Illini Hospital, Silvis, Illinois. A Forensic Toxicology Fatal Accident Report was prepared on the pilot by the Federal Aviation Administration's Civil Aeromedical Institute. The report indicated the following results: No Carboxyhemoglobin detected in blood. No Cyanide detected in blood. No Ethanol detected in urine. 9.100 (ug/ml, ug/g) Salicylate detected in blood. 1426.200 (ug/ml, ug/g) Salicylate detected in urine. The levels of Salicylate detected in the blood and urine was normal. Salicylate is found in aspirin. Tests and Research A pilot reported he had flight tested and performed stalls in the airplane. He reported that during stalls the airplane broke to the left with an immediate drop of the nose. He reported that it was a very pronounced roll to the left during the stall. The modification that the pilot/builder had made to the impulse fuel pump was examined. The examination revealed the following: "Modification pulse pump apparently consists only of the addition of a third outlet. The modification alone would not be a problem, but the way the two pumps were plumbed together, each pump was relying on the other as a check valve. When pressure was applied to the inlet of the electric pump, fuel was force backwards out of the pulse pump. When vacuum was applied to the inlet of the electric pump, fuel was drawn backwards through the electric pump" "The way the pumps were plumbed, the pulse pump worked correctly only if the check valve's strainer at the end of the electric pump's inlet was closed." The impulse fuel pump was tested on a similar engine. With the blocked one way check valve removed from the fuel line leading to the impulse pump, the impulse pump operated normally. Additional Information The Federal Aviation Administration was a party to the investigation. The aircraft was released to the Gen-Air Park Airport manager on August 5, 1996.
a loos of power due to a blocked fuel line and the pilot's failure to maintain airspeed.
Source: NTSB Aviation Accident Database
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