Hawkinsville, GA, USA
N6216M
THRUSH S2R
The pilot reported that during the takeoff roll for the aerial application flight, the airplane used more runway than normal, and that after takeoff it “didn’t seem to produce power as usual.” He began a right turn and noticed “the power and airspeed [were] slowing.” He checked the gauges and noticed that that the fuel pressure was fluctuating, and then turned on the emergency fuel pump. He then jettisoned the chemical load, and the airplane continued to descend until it impacted trees. A postaccident examination of the airplane found that the electric main fuel pump did not operate. Disassembly of the pump’s electric motor revealed that the carbon brushes had completely worn away, with no brush material remaining in either of the two brush holders. Examination of the engine revealed no anomalies that would have precluded normal operation. Given that the pilot reported a longer than usual takeoff roll and a reduction in engine power throughout the flight, the pump may not have been operating properly or at all before takeoff. The reduction in power may have been due to the engine operating on only its internal fuel pump. The pilot did not report that the condition improved after he activated the emergency fuel pump. Whether or not the emergency pump had no effect or there was insufficient time to recover before the airplane struck trees could not be determined.
On May 5, 2022, at 0930 eastern daylight time, a Thrush S2R-H80, N6216M, was substantially damaged when it was involved in an accident in Hawkinsville, Georgia. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 137 aerial application flight. The pilot reported that he loaded the airplane with 325 gallons of chemicals and water for the planned aerial application flight. During the takeoff roll, the pilot noticed that the airplane used more runway than normal to lift off. After takeoff, he noticed that the engine “didn’t seem to produce power as usual.” He began a right turn and noticed “the power and airspeed [were] slowing,” after which he stopped the turn and attempted to keep the airplane as straight and level as possible. He checked the gauges and saw that the fuel pressure was fluctuating and immediately turned on the emergency fuel boost pump. He jettisoned the chemical load, but the airplane continued to lose altitude and airspeed until it struck trees and terrain. A postaccident examination of the airplane revealed that the electric airframe main fuel pump would not rotate when supplied with electrical power. The emergency fuel pump (of the same make/model as the main) rotated when supplied with electrical power. After partially disassembling the main and emergency pump electric motors, black powdery material consistent with carbon dust was found inside of both motor housings. (See Figures 1 and 2) The two brush holders inside the main pump motor were empty; that is, no brush material remained. The push block and spring from one of the holders was missing. The emergency pump’s brush assemblies were intact, with about 3/16” of material remaining on each brush. Figure 1. Main Fuel Pump Motor Figure 2. Emergency Fuel Pump Motor The engine gas generator rotor could not be rotated. A borescope examination of the gas generator turbine blades revealed that the blades were present and intact. About half of the power turbine blades were found bent in the direction of rotation, consistent with impact damage. No preimpact anomalies that would have precluded normal engine operation were found. The airframe mounted fuel filter was undamaged and absent of debris. The filter cavity was clean and full of fuel. The maintenance records available did not contain any service history or installation date for the electric fuel pumps. The data plates on the pumps indicated the main pump was manufactured on March 24, 2017, and the emergency pump was manufactured on December 12, 2016. Whether the pumps were original, replacements, or overhauled, could not be determined. The airplane was manufactured in 2017. The airplane manufacturer did not prescribe a life limit or overhaul schedule for the fuel pumps. The airplane maintenance manual specified that they should be operated and checked for leaks during the annual/100-hour inspection. Additionally, the engine start checklist specified that both pumps are to be operated (independently), and the resulting fuel pressure from each checked, before every engine start. According to the airframe maintenance manual: The GE H80-100 engine is designed to have fuel fed to its inlet under pressure, but it will run normally without the airplane supplying fuel under pressure. The engine manufacturer has placed a limit of 100 [hours] on the engine running without pressurized inlet fuel, however. This is because the engine fuel pump will cavitate without inlet fuel pressure, which eventually damages the pump.
A failure of the electric main fuel pump due to the carbon brushes having completely worn away.
Source: NTSB Aviation Accident Database
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