CALEDONIA, MS, USA
N45205
Air Tractor AT-401
The pilot was spraying chemicals on a cotton field at an altitude of 300 ft. An hour and a half into the flight, he entered a right turn and the engine lost power. During the initiated forced landing, the right wing collided with a tree. The airplane spun to the right, colliding with the ground nose first, bounced several times, then came to rest. Post-examination of the engine revealed that there was an interruption of the direct drive fuel control (DDFC) gear-train due to a loss of mechanical contact between the teeth of the second and third DDFC gears. The cause for the interference was believed to have been due to excessive loading of the forward gear teeth of the third DDFC gear resulting in loss of material from the third DDFC gear. No assembly, dimensional or material defects were identified which would contribute to excessive loading or interference between the second and third DDFC gears.
On September 13, 1999, at 0815 central daylight time, an Air Tractor AT-401, N45205, collided with the ground following a loss of engine power near Caledonia, Mississippi. The agricultural flight was operated by the commercial pilot under the provisions of Title 14 CFR Part 137, and visual flight rules. Visual meteorological conditions prevailed at the time of the accident and no flight plan was filed. The airplane sustained substantial damage and the pilot was not injured. The flight departed Columbus, Mississippi, at approximately 0645. According to the pilot, he was spraying chemicals on a cotton field at an altitude of approximately 300 feet. An hour and a half into the flight, he entered a right turn and the engine began to lose power. He stated that the engine sounded like it was "slowing down to nothing," and that no smoke was present. He turned on the fuel boost pump and igniter switch, which had no effect. He applied flaps, feathered the propeller, and initiated a forced landing. Realizing he would be unable to clear a hedgerow, he retracted the flaps; however, the right wing collided with a tree. The airplane spun to the right before colliding with the ground nose first and then bounced several times. It came to rest facing the direction of approach with substantial damage to both wings, the empennage, and the propeller and engine assemblies. According to the FAA, examination of the accident site revealed that the airplane rested upright on a west/northwest heading. The empennage was offset to the right with considerable damage. The wings and propeller sustained impact damage and the engine mounts were broken. There was a considerable amount of fuel in both the left and right wing tanks. A sample of fuel was drained from each wing and no evidence of contamination was found. The engine fuel pump strainer/filter was removed and inspected with no evidence of metal or other contamination. An oil line from the front of the engine gearbox was removed in order to view the internal gears. The propeller was rotated, which produced a grinding/rattling sound, but the gearbox gears did not rotate. The engine was sent to the Honeywell Product Safety and Integrity facility in Phoenix, Arizona, and was examined on November 30, 1999. Upon initial examination, the engine power section and propeller shaft was free to rotate. The direct drive fuel control (DDFC) gear was examined by removing the external oil scavenge elbow and rotating the power section while observing the scavenge pump gear rotor element within the gearbox. The oil pump scavenge pump element did not rotate when the power section was turned. An internal examination revealed that there was a loss of mechanical contact between the teeth of the second and third DDFC gears. The examination also disclosed that there was a loss of gear tooth material from both gears. There were contaminates and debris found in the engine lubrication system. No assembly, dimensional or material defects were identified. According to the pilot, the airplane experienced a similar incident on September 7, 1999, a week earlier. The engine lost power while the operator was spraying and the pilot made an emergency landing without sustaining damage. The engine was removed and taken to Smyrna Air Center in Smyrna, Tennessee, for examination and repairs. The examination found the torque sensor shaft that drives the fuel pump sheared. Repairs were made and the airplane was returned to service on September 9, 1999. Since the repairs were made, the airplane had flown approximately 14 hours.
The failure of the fuel control gear train due to oil contamination. A factor was Inadequate maintenance.
Source: NTSB Aviation Accident Database
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