HUFFMAN, TX, USA
N501JS
Air Tractor AT-400
After completing aerial application, the pilot entered a right base turn to final approach for landing at a private dirt airstrip. During the turn, a witness observed the 'the left wing' go down and 'also the nose.' The airplane crashed in a left wing low (descending) attitude. The pilot/mechanic had performed maintenance on the aircraft and had certified on March 1, 1995, that the 'aircraft has been inspected in accordance with an annual inspection and was determined to be in an airworthy condition.' Postaccident examination revealed that the empennage flight controls exhibited severe corrosion. The left elevator bellcrank assembly elevator horn was found separated from the control rod elevator torque tube. The left stabilizer strut lower attachment was separated where the tube of the strut was welded to the 'U' shaped attachment bracket. Examination of the 'U' bracket only revealed corroded remnants of the forward bracket and no evidence of the edge welds that joined the bracket pieces together. Fracture surfaces on the elevator horn were consistent with overstress separation. Manufacturing specifications required a 0.080 inch steel sheet for the elevator horn. Over the majority of the horn and near the control rod attachment fracture, the thickness was as low as 0.059 inches.
HISTORY OF FLIGHT On July 2, 1996, at 1030 central daylight time, an Air Tractor AT-400, N501JS, registered to and operated by Associated Aerial Applicators of Dayton, Texas, as a Title 14 CFR Part 137 aerial application flight, impacted terrain following a loss of control near Huffman, Texas. The commercial pilot received fatal injuries and the airplane sustained substantial damage. The pilot began the local aerial application flights for the day about 1 hour 15 minutes prior to the accident. Visual meteorological conditions prevailed and a flight plan was not filed. During personal interviews, conducted by the investigator-in-charge, witnesses and operator personnel reported that the pilot was spraying the grain fields with fertilizer. Spray runs were being conducted in an east to west race track pattern. The reloading takeoff and landings were made to a private north to south dirt airstrip (Tricky Airstrip). Upon completing a spray run to the east, the airplane entered a right base turn to final for landing to the north. During the turn a witness observed the "the left wing" go down and "also the nose." The witness further stated that the engine was running and a post-impact engine fire started which was extinguished by a witness. The pilot was wearing a helmet; however chin straps were not on the helmet. PERSONNEL INFORMATION According to FAA records and a friend, the pilot's total flight time was 25,000 flight hours. The pilot was a licensed airframe and powerplant mechanic and performed the maintenance on his aircraft. The pilot's logbooks were not made available to the Board. AIRCRAFT INFORMATION The Air Tractor had been operated and maintained by Associated Aerial Applicators since the airplane was purchased in May 1985. Maintenance records presented to the Board indicated that the pilot/mechanic certified on March 1, 1995, that the "aircraft has been inspected in accordance with an annual inspection and was determined to be in an airworthy condition." Records did not indicate any additional inspections. Company spraying records for June 1996 indicated that the pilot had flown the aircraft almost every day during aerial application flights. The aerial application flights, in June 1996, included flights on the 21st from 1130 until 1430 whereby the airplane was loaded and reloaded from the Tricky Airstrip. WRECKAGE AND IMPACT INFORMATION The aircraft impacted the ground and came to rest on a measured magnetic heading of 230 degrees, approximately 150 yards from the south end of the airstrip. All aircraft components were located within 100 feet of an initial ground scar. The initial ground scar was of the left wing and was 38 feet long. The tail section of the aircraft had separated from the aircraft along with the left aileron. (See wreckage diagram) Seat deformation was downward and forward. The seat belt and shoulder harness was fastened; however, the shoulder harness was frayed along the edges. Wing skin was crushed and buckled. An elevator spring and the interconnect rods for the ailerons and elevators were not found at the site. One propeller blade exhibited aft bending and the other blade was twisted and bent. Physical evidence of fire was noted at the engine in the vicinity of the fuel lines. Engine rotational continuity was confirmed and fuel was found at the fuel heater and the fuel control unit. Flight control continuity could not be established. Empennage flight controls exhibited corrosion and examination of the left elevator bellcrank assembly revealed that the left elevator horn was separated from the control rod elevator torque tube. The left elevator horn and the elevator torque tube were forwarded to the NTSB Metallurgical Laboratory for examination. The NTSB Metallurgists found "extensive corrosion attack and corrosion products" on the elevator components. The elevator horn "fracture surfaces were consistent with an overstress separation." Manufacturer specifications require that the elevator horn be manufactured from 0.080 inch thick alloy steel sheet. Over the majority of the horn and near the control rod attachment fracture, the "thickness varied and in some locations was as low as 0.059 inches thick." In August 1996, the Board examined the flight control system. The left stabilizer strut exhibited corrosion and was separated at the lower attachment assembly. The left and right stabilizer struts lower attachment assemblies were forwarded to the NTSB Metallurgical Laboratory for examination. The NTSB Metallurgists found that the exterior pieces exhibited "some surface corrosion, varying from moderate to severe." The entire lower end of the left elevator strut and the separation area of the attachment bracket were covered by a "thick layer of corrosion scale." Close examination of the "U" bracket "only found corroded remnants of the forward bracket and no evidence of the edge welds that joined the bracket pieces together." MEDICAL AND PATHOLOGICAL INFORMATION The autopsy was performed by Tommy J. Brown, D. O., of the Office of the Medical Examiner of Harris County at Houston, Texas. Toxicology testing was performed by the FAA Civil Aeromedical Institute at Oklahoma City, Oklahoma. Toxicological findings were negative. ADDITIONAL DATA The aircraft was released to the owner's representative.
corroded flight control components, due to the operator's inadequate maintenance and inspection of the airplane; the pilot's failure to follow procedures and directives, by flying the airplane without proper maintenance and annual inspection; and subsequent failure of a corroded flight control component.
Source: NTSB Aviation Accident Database
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