History of Flight
On May 28, 2017, at approximately 0910 central daylight time, a Piper PA36-300 airplane, registered as N3711E, was substantially damaged when it struck a cotton field near El Campo, Texas. The commercial-rated pilot sustained serious injuries. The aircraft was operated by Trade Wind Ag Service Inc. under Title 14 Code of Federal Regulations Part 137 for aerial application. Visual meteorological conditions were present, and no flight plan was filed. The flight departed a private field around 0900.
The owner of the accident airplane, who was conducting agricultural operations in another aircraft nearby, noticed the absence of the accident airplane and flew to investigate. He spotted the wreckage at approximately 0920. Two witnesses in the area reported seeing or hearing the airplane shortly before the accident, describing popping noises or loud shotgun-like sounds.
According to the Federal Aviation Administration (FAA) inspector who responded, the airplane impacted the ground in a nose-low, left wing-low attitude. The wreckage lay in a field adjacent to the pilot's intended application area, with debris extending about 60 feet from the initial impact point to the main wreckage. The engine, propeller assembly, and both main landing gear separated from the airframe. The right wing partially separated, and the left wing was crushed aft and buckled.
Months after the accident, the pilot could not recall specific details. He remembered losing altitude, attempting to level the wings, and trying to egress through the window. Prior to the flight, he recalled difficulty starting the engine—once started, it produced a deep rumble with popping sounds, but eventually cleared and ran without issue.
Wreckage Examination
The wreckage was recovered to a secure facility and examined by investigators from the National Transportation Safety Board (NTSB) and Lycoming. The fuel selector valve was in the "On" position with definitive detents, moving without hesitation. Both fuel tanks were compromised during impact, and wing skins exhibited hydraulic deformation consistent with fuel being present at impact. Internal foam baffles in both tanks were discolored and deteriorated, disintegrating into fine particles upon touch.
The engine assembly was impact-damaged, with dirt embedded around the case and cylinders. Left magneto leads were damaged and could not be functionally tested, but both magnetos produced sparks on a test bench. Valve covers, upper spark plugs, and injector nozzles were removed for examination. Injector nozzles 1, 2, and 6 were obstructed with an unknown substance.
Manual rotation of the engine via the propeller showed valve movement on all cylinders. Tactile compression was noted on all cylinders except No. 1. Accessory gears rotated, confirming valve train and crankshaft continuity. No fuel was found in engine fuel lines, but trace fuel was present in the engine-driven fuel pump and 5 to 10 ml in the boost pump output line. The fuel filter, fuel screen, and throttle body screen were free of visible contaminants. Liquid in the fuel flow divider tested positive for water using water-finding paste.
The fuel injection servo was examined by an NTSB investigator and a representative from Precision Airmotive LLC. The flange, mixture shaft, and multiple fittings were impact-damaged. The unit was tested on a field flow bench with Stoddard solvent; a leak at the mixture control shaft was attributed to impact damage. Pressures at various simulated engine RPMs were consistent with the mixture control valve in the idle or off position, confirmed during disassembly. Both the drain jet and venturi drain were plugged or partially plugged with an unknown substance. According to Precision Airmotive LLC, these conditions would result in a rich mixture.
Additional Information
The owner/operator had purchased the airplane about a year before the accident. Periodic engine starting issues were addressed by adjusting spark plug gaps. During flight, fuel pressure would decrease and trigger a low-fuel-pressure light; turning on the electric fuel pump would restore pressure. Five days before the accident, routine maintenance revealed blue foam in the fuel filter, identified as originating from the internal foam baffles in the fuel tanks. The filter was cleaned and checked after each subsequent flight, with no further findings. The foam baffles were not replaced at that time. Piper Service Bulletin 713, dated May 11, 1981, recommends inspection and maintenance of fuel cells due to the potential for foam particles to contaminate the fuel system when baffles discolor and deteriorate.