Cameron, LA, USA
N350AL
Bell 206L-3
The helicopter was in cruise flight over the Gulf of Mexico when it began to vibrate and shudder. The pilot lowered the collective control to initiate an autorotation and the engine lost power. During the ensuing autorotation, the helicopter's floats were deployed. The pilot attempted to decelerate the helicopter; however, the controls became stiff, and subsequently, the helicopter hit the water hard. Examination of the helicopter's fuel system revealed that the fuel nozzle inlet screen was collapsed and the screen was 80 to 90% contaminated with a brown material with a polymeric-like to varnish-like appearance. The screen was examined by a laboratory, and it was determined that DIEGME, a fuel additive used as an icing inhibitor, was present on the screen. The helicopter's operating environment is such that salt water could have been introduced into the fuel system. The presence of water and fuel would allow bacteria to grow. The combination of bacterial growth, DIEGME, and water resulted in the formation of an "apple-jelly" type material, which then adhered to the fuel system components (fuel nozzle screen). The blockage and collapse of the fuel nozzle screen resulted in an interruption of fuel flow, and the subsequent loss of engine power.
On August 24, 2001, at 0715 central daylight time, a Bell 206L-3 helicopter, N350AL, was destroyed when it impacted water during a hard landing following a loss of engine power 6 miles south of Cameron, Louisiana, in the Gulf of Mexico. The helicopter was registered to and operated by Air Logistics LLC, of New Iberia, Louisiana. The commercial pilot and his one passenger sustained serious injuries. Visual meteorological conditions prevailed, and a company visual flight rules (VFR) flight plan was filed for the 14 Code of Federal Regulations Part 135 on-demand air taxi flight. The flight originated from the Air Logistics Heliport, Cameron, Louisiana, at 0709, and was destined for West Cameron 149, an offshore oil platform located in the Gulf of Mexico. According to the pilot, the helicopter was in cruise flight when it began to "vibrate and shudder." He lowered the collective control to initiate an autorotation, and the engine lost power. During the ensuing autorotation, the helicopter's floats were deployed. The pilot attempted to decelerate the helicopter; however, the controls became stiff, and subsequently, the helicopter "hit the water hard." On July 20, 2001, the airframe and Rolls-Royce CAE250-C30 engine underwent their last inspection, according to Air Logistics’ Approved Inspection Program (AAIP). On August 20, 2001, the following pilot discrepancy was recorded in the aircraft flight log: Fuel gauge erratic. Maintenance personnel removed all fuel probes, removed moisture from them, re-installed them in the helicopter, calibrated the fuel system, and the helicopter was returned to service. On August 23, 2001, the following pilot discrepancies were recorded in the aircraft flight log (9,425.1 hours total time): Fuel gauge became erratic after 3rd flight and during the engine start procedure the engine shuts down as it nears 40% N1. Maintenance personnel cleaned the center fuel probe and removed and re-installed the fuel nozzle. At the time of the accident, the airframe had accumulated a total of 9,429.4 hours, and the engine had accumulated a total of 8,348.8 hours (991.1 hours since overhaul). The helicopter was recovered from the Gulf of Mexico and examined at the Air Logistics facility in New Iberia, Louisiana, under supervision of an FAA inspector. The helicopter's airframe and engine, with exception of the tail boom from the horizontal stabilizer rearward and a portion of the main rotor blade were accounted for. Flight control continuity was established from the cyclic and collective controls to the main rotor system. The engine was examined and there was no evidence of a catastrophic failure. The airframe fuel filter and the fuel strainer in the fuel pump were clear and free of contaminants. The fuel pump, fuel control unit, govoner and fuel nozzle were each placed in a test stand, and met the manufacturer's specifications when operated. Additionally, the N1, N2 and NR tachometer generators were placed in a test stand and met manufacturer's specifications when operated. On September 25th and 26th, 2001, the hydraulic pump and three hydraulic servos were examined at Bell Helicopter's facility in Hurst, Texas, under supervision of the NTSB investigator-in-charge. The hydraulic pump and the three hydraulic servos were observed intact and then placed in a test stand. Each unit operated within the manufacturer's specifications. Near the time of this accident two additional Air Logistic's helicopters, a Bell 407, N417AL, and a Bell 206L-3, N2616, experienced engine failure accidents/incidents. Examination of these helicopter's fuel system components, specifically the fuel nozzle inlet screens, revealed that they were collapsed and contaminated with a brown material that appeared polymeric-like to varnish-like in appearance. The material was determined to be DIEGME, a fuel additive used as an icing inhibitor. Further testing on fuel samples from N417AL revealed that salt water and DIEGME were present in the fuel. The water in the fuel would allow bacteria to grow. The combination of bacterial growth, DIEGME, and water is conducive to the formation of an "apple-jelly" type material, which could then adhere to the fuel system components. The blockage of a fuel nozzle screen can result in its collapse and a subsequent interruption of fuel flow. The fuel nozzle inlet screen from N350AL was re-examined and confirmed to be collapsed. Additionally, 80 and 90% of the screen surface was observed to be contaminated with a brown material with a polymeric-like to varnish-like appearance, similar to that observed in the previously mentioned helicopters. The screen was examined by Heritage Laboratories, and it was determined that DIEGME was present on the screen.
fuel contamination due to the combination of DIEGME, water, and bacterial growth, which resulted in formation of an apple-jelly type material that blocked the fuel nozzle screen and led to a loss of engine power.
Source: NTSB Aviation Accident Database
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