HISTORY OF FLIGHT
On May 28, 2017, about 0910 central daylight time, a Piper PA36-300 airplane, N3711E, was substantially damaged when it impacted a cotton field near El Campo, Texas. The commercial-rated pilot sustained serious injuries. The airplane was owned and operated, by Trade Wind Ag Service Inc., under the provisions of Title 14 Code of Federal Regulations Part 137. Visual meteorological conditions prevailed and no Federal Aviation Administration (FAA) flight plan had been filed for the flight. The aerial application flight departed a private field about 0900.
The owner of the accident airplane was conducting agricultural flight operations in another airplane, over a nearby field, and had not seen the accident airplane for a while. He flew to check on the pilot and spotted the airplane wreckage about 0920. Two witnesses in the area reported seeing or hearing the airplane flying just prior to the accident and could hear popping noises or loud shot gun-type popping sounds.
According to the FAA inspector who responded to the accident, the airplane hit the ground in a nose low, left wing low attitude. The airplane wreckage was in the field adjacent to where the pilot was conducting aerial applications. Debris extended for about 60 feet from the initial impact point to the main wreckage. The engine and propeller assembly, and both main landing gear separated from the airframe. The right wing separated partially from the fuselage and the left wing was crushed aft and buckled.
Months following the accident, the pilot could not recall details of the accident. He did recall losing altitude and trying to level the wings. He also recalled trying to egress from the airplane window. Prior to the accident flight, he recalled having a difficult time starting the engine – once the engine started there was a deep rumble with popping, but it eventually cleared, and the engine ran without issue or hesitation.
WRECKAGE INFORMATION
The wreckage was recovered to a secure storage facility and examined by a National Transportation Safety Board (NTSB) investigator and an investigator from Lycoming. The fuel selector valve was in the "On" position. The detents were definitive when tested and the fuel selector valve lever moved without hesitation or sticking. Both fuel tanks were compromised during the impact sequence and the wing skins exhibited hydraulic deformation, consistent with fuel being present at the time of impact. The internal foam baffles in both fuel tanks were discolored and deteriorated. When touched by hand, the baffles would disintegrate into very fine particles.
The engine assembly was impact damaged and had dirt imbedded around the case and cylinders of the engine. The left magneto leads were impact damaged and could not be functionally tested. Both the left and right magneto produced a spark at the end of each lead when placed on a test bench and activated. The valve covers, the upper bank of spark plugs, and the injector nozzles were removed to facilitate the examination. Injector nozzle Nos. 1, 2, and 6 were obstructed with an unknown substance.
The engine was rotated through by hand at the propeller. Valve movement was noted on all cylinders. Tactile compression was observed at all, but the No. 1, cylinder. The accessory gears at the rear of the engine rotated and confirmed valve train and crankshaft continuity.
There was no evidence of fuel in the engine fuel lines; however, trace fuel was noted in the engine driven fuel pump and 5 to 10 ml of fuel was noted in the boost pump output line. The fuel filter, fuel screen, and the throttle body screen were free of visible contaminants. Liquid in the fuel flow divider tested positive for water when tested with a water-finding paste.
The fuel injection servo was examined by an NTSB investigator and an investigator from Precision Airmotive LLC. The flange, mixture shaft, and multiple fittings on the fuel injection servo were impact damaged. The unit was placed on a field flow bench and stoddard solvent was used to test the unit for flow and pressure. A leak was noted at the mixture control shaft; however, it was attributed to impact damage to the unit. The pressures at varying simulated engine rpms were consistent with the mixture control valve in the idle or off position. This position was later confirmed during the disassembly of the unit. Both the drain jet and the venturi drain were plugged and partially plugged, respectively, with an unknown substance. According to Precision Airmotive LLC, both conditions would result in a rich mixture.
ADDITIONAL INFORMATION
According to the owner/operator of the airplane, they had purchased the airplane about a year prior to the accident. On occasion they had issues starting the engine and this was remedied by adjusting the gap on the spark plugs. During flight, the fuel pressure would decrease, and the low fuel pressure light would illuminate. If the pilot turned the fuel pump on, the light would go out, and the fuel pressure would increase. During routine maintenance, 5 days prior to the accident, a mechanic found blue foam, he identified as coming from the internal foam baffles in the fuel tanks, in the fuel filter at the engine. The filter was cleaned and then checked periodically after every flight without further findings. The internal foam baffles were not replaced at the time of the finding.
Piper Service Bulletin 713, dated May 11, 1981, calls for the inspection and maintenance of the fuel cells due to the possibility of foam particles contaminating the fuel system, when they start to discolor and deteriorate.