Henley, MO, USA
N150U
NORTH AMERICAN AT-6D
The airline transport pilot reported that, about 30 minutes into the local flight, the engine experienced a total loss of power, and he conducted a forced landing to a powerline cut. He stated that the airplane was at low altitude at the time of the loss of engine power because he had been taking photos of a friend's farm. Two witnesses observed the airplane conducting aerobatic maneuvers during the flight. One of the witnesses stated that the airplane was flying so low that it startled her horses as it passed overhead. She then observed the airplane roll inverted; shortly thereafter, the engine became silent. The airplane lost altitude while still inverted and impacted trees. Examination of the wreckage revealed no preimpact mechanical malfunctions or anomalies that would have precluded normal operation. The airplane's operating instructions stated that, "Inverted flying must be limited to 10 seconds because of engine difficulties resulting from prolonged inverted flight." Because no anomalies were found during the examination, it is likely that the loss of engine power was a result of fuel disruption to the engine during the extended inverted flight.
On June 19, 2016, about 1440 central daylight time, a North American AT-6D, N150U, sustained substantial damage when it impacted trees while maneuvering at a low altitude near Henley, Missouri. The pilot and passenger received serious injuries. The airplane was registered to Ozark Management Inc. and operated by the pilot under the 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed and no flight plan was filed. The airplane departed from the Jefferson City Memorial Airport (JEF), Jefferson City, Missouri, at an unknown time on a local flight. A deputy of the Cole County Sheriff's Department reported that about 1410 he observed an aircraft flying about 1,500 ft above ground level (agl). He stated that he observed the airplane perform an aerobatic maneuver – a loop. The airplane then departed from his view to the north behind his car. He rolled down his car window and said that the engine sounded like an "old P-51 Mustang." The deputy was later notified by dispatch about 1445 that an airplane accident had occurred. He arrived at the scene about 1453. He noted that the accident aircraft was same type of WWII airplane and had the same markings as the one he had observed at 1410. A Federal Aviation Administration (FAA) inspector interviewed a witness who observed the airplane before it crashed. The witness stated that she observed the airplane flying at a low level over the farm fields near her property. She stated that the airplane was so low that it startled her horses as it flew overhead. She stated that the engine was operating as it flew overhead. Then she observed the airplane fly inverted, but she was not sure how long it was inverted. The airplane's engine became silent shortly after it went inverted. The airplane lost altitude while still inverted and she heard a crashing sound as it impacted the trees. FAA inspectors examined the airplane wreckage at the accident site. The inspectors reported that the airplane crashed into a wooded area. The initial point of impact was a tree about 325 ft south of the main wreckage. The debris field extended about 300 feet south of the aircraft's final resting place. There was a strong odor of fuel and oil in the immediate area of the aircraft fuselage which was found inverted in a clearing. The left wing was separated from the fuselage and was lying adjacent to the fuselage. The right wing had separated from the fuselage and was lying approximately 50 feet south of the aircraft. The main landing gear were still mounted to the underwing structures and were in the retracted position. The forward cockpit had sustained significant impact damage. The pilot seat was intact, but broken from its mount with the seatbelts intact. The instrument panel was broken and most the instrument gauge glass was broken; the switches were crushed; and all the circuit breakers were pushed in (not popped). The fuel selector was set to the 20-gallon reserve setting. The flap handle was found in the up position; the throttle was full open; the mixture was full rich; and the RPM setting was in the mid position between increase and decrease. The rear cockpit had minor damage to the structure surrounding the occupant. The seat was intact on its mount and the seatbelts were also intact. The cockpit glass on the entire cockpit was broken. The aircraft engine cowling was severely damaged. The propeller blades were bent aft and had minimal chordwise scratching or leading edge nicks or gouges. The engine fuel filter assembly was examined. The filter had minor debris present. The electric fuel pump was examined and the shaft was manually rotated. The fuel pump operated properly and moved the residual fuel it contained from one side of the pump to the other. The North American AT-6D Flight Operating Instructions listed prohibited maneuvers. The prohibited maneuvers included: 1) outside loops, 2) inverted flight in excess of 10 seconds, 3) snap rolls in excess of 130 mph, 4) slow rolls in excess of 190 mph are prohibited, and 5) spins and stalls when normal gross weight is exceeded. The operating instructions also included this statement: "Inverted flying must be limited to 10 seconds because of engine difficulties resulting from prolonged inverted flight." FAA inspectors interviewed the pilot and passenger. Neither remembered what occurred during the accident, but they stated that no aerobatic maneuvers were flown during the accident flight. In a written statement, the pilot made the following statement, "Sightseeing trip, about 30 minutes into the flight the engine made a pop and the prop stopped. I was low from taking pictures of a friend's farm. We forced landed into a powerline cut. That's the last I remember." The pilot also stated that the cause of the engine's loss of power could be attributed to the corrosion of the supercharger bearings, which when they fail, it causes the supercharger to wobble. The supercharger then starts to contact the engine case causing fine metal filings to build in the oil which results in the engine failing from oil starvation. At 1353, the surface weather observation at JEF was: wind 200 degrees at 10 kts; 10 miles visibility; few clouds at 5,500 ft; scattered clouds at 7,000 ft; temperature 32 degrees C; dew point 19 degrees C; altimeter 30.17 inches of mercury.
The pilot’s decision to conduct extended inverted flight, which resulted in a total loss of engine power due to fuel flow disruption. Contributing to the accident was his decision to conduct aerobatic maneuvers at low altitude, which precluded him from selecting a suitable landing site following the total loss of engine power.
Source: NTSB Aviation Accident Database
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