On May 16, 2005, at 1145 Hawaiian standard time, a Hughes 369D helicopter, N611WA, sustained substantial damage during an autorotational landing on a shoreline near Kihei, Hawaii. A partial loss of engine power during cruise flight preceded the autorotational landing. The airline transport helicopter pilot and his three passengers were not injured. The helicopter was registered to, and operated by, WindWard Aviation, Inc., Kahului, Hawaii, as a personal flight under the provisions of 14 CFR Part 91. The local flight departed Kahului 36 minutes prior to the accident. Use your browsers 'back' function to return to synopsisReturn to Query Page
According to the pilot, they were in cruise flight over McGregor Point on the island of Maui when the engine began to "wind down." The engine did not completely lose power, but was not producing enough to maintain flight. The pilot elected to autorotate to the shoreline near McGregor Point. After touching down, the helicopter slid back on the slippery rocks and the tail rotor blades impacted the ground resulting in damage to the blades and shearing of the tail rotor drive shaft.
The helicopter was removed from the shoreline prior to high tide and was taken to the Kahului Airport. The Federal Aviation Administration (FAA) inspectors, who responded to the accident site, found the fuel nozzle filter 30 percent blocked with a brown substance. Disassembly and closer examination of the fuel system revealed about 10 percent contamination of the fuel control unit filter and no contamination of the fuel pump filter. The fuel from the tank was pumped into a 55-gallon drum and showed no evidence of contamination. The remaining fuel was drained from the tank by removing the tank sump drain. This fuel contained approximately 1 ounce of a brownish watery substance. The fuel cells were examined and the same brownish watery substance was noted on the upslope side of the ribs and folds in the bottom of the fuel cells. The fuel boost pump was removed and the entire inlet screen of the pump was completely obscured and blocked with a brown contaminant and a white cotton-like material, and the fuel tank outlet line contained brown substance similar to that found at the nozzle.
The 369 series of helicopters has one two-cell fuel tank. The airframe fuel system has a fuel tank boost pump to provide positive-pressure fuel delivery to the engine for starting. The engine-driven fuel pump provides high-pressure fuel to the fuel control unit (FCU), which meters fuel to the fuel nozzle. The fuel nozzle is a two-stage single-barrel fuel delivery device providing fuel to the engine for starting and fuel spray for continuous operation. The Allison 250 series engine has three fuel straining devices to prevent contaminants in the fuel from reaching the engine. The fuel pump has a two-stage filter with a bypass and pressure sensor to activate a warning light in the cockpit if the fuel flow through the filter is obstructed (impending bypass). The FCU has an inlet fuel screen with a bypass feature with no associated warning indication. The fuel nozzle has a fuel screen with neither a bypass feature nor an associated warning indicator.
According to the operator, the helicopter was utilized in crop dusting operations on the island of Kauai on the 12th and 13th. During that time, the helicopter was refueled from the company's 500-gallon remotely located fuel tank. The fuel tank was equipped with fuel filters and sumps; however, the fueler assisting during the operations on the 12th and 13th, was not trained in the company's normal operations and had not conducted the daily quality assurance checks, and had not sumped the tank, filters, and hoses. In addition, it was later learned that the fuel tank cover was broken, allowing contaminants and water to enter the system.
Later on the 13th, the helicopter was refueled at Air Services at Lihue Airport and flew to Honolulu, Hawaii. In Honolulu, the helicopter was again fueled with 20 gallons. When the pilot attempted to depart Honolulu to return to Maui, the engine would not start. The pilot drained a fuel sample and found some brown watery contamination. The operator contacted a maintenance facility in Honolulu and requested that they purge and clean the fuel system. After the fuel tank was drained, fuel system purged, the fuel nozzle replaced, and the fuel tank refueled, the helicopter was returned to service. The helicopter was flown back to Maui where the fuel tank was again topped off. The helicopter was not utilized again until the accident flight. On the morning of the accident, the fuel nozzle was again replaced with a new fuel nozzle. The pilot reported finding no contaminants during his preflight inspection and examination of the fuel sample.
Review of the helicopter maintenance manual, under the section titled "Fuel System Fault Isolation," if the helicopter experiences a fuel contamination, the corrective action is to "inspect and clean the fuel cell and start pump inlet screens if large amounts of foreign material are found in the engine driven fuel pump filter (or the optional airframe fuel filter if installed)." The accident helicopter was not equipped with the optional airframe fuel filter. The maintenance endorsement for the maintenance performed in Honolulu indicated that the fuel nozzle was removed for fuel contamination and "fuel filter clean & drain fuel sys[tem]. Install o/h [overhauled] fuel nozzle & new fuel filter. Bleed fuel sys[tem]." The maintenance personnel later reported that they had not opened and cleaned the fuel tank.
According to printed literature from fuel system suppliers, by their very nature, fuels such as diesel and Jet Fuel contain water. There is a microscopic fungi growth that can occur either throughout the fuel or at the interface between visible water and the bottom of the fuel layer. The fungi will grow rapidly, requiring only trace amounts of water and minerals for sustainability. Once this growth begins, the fungi turns into a type of slime, which can be of any color although is likely to be black, green, or brown. With agitation, such as that experienced during filling, the fungi will be redistributed throughout the fuel system where they will cling to walls and supporting structures. As they grow, the fungi will chemically alter the fuel to produce water, sludge, and acidic byproducts. A myriad of problems within the fuel system can occur including clogging of the various fuel filters, and fuel system components.
This event was not the first time fuel contamination has resulted in a helicopter accident in the State of Hawaii. In the past 11 years there have been three fuel contamination events that have resulted in one fatality, four serious injuries, one destroyed helicopter, and two substantially damaged helicopters.
As a result of some of these accidents, the National Transportation Safety Board issued Safety Recommendations A-98-84 through -86, which resulted in the Airworthiness Directive (AD) 2004-24-09 (effective January 5, 2005). That AD directs operators to inspect the fuel nozzle screens on Allison 250-B and 250-C series turboshaft and turboprop engines for contamination, and to inspect and clean the entire aircraft fuel system before further flight if there is any contamination on the screen.
According to the FAA inspector, the operator had complied with Airworthiness Directive 2004-24-09.