LAX94FA197

The pilot reported that while maneuvering near a waterfall on a sight-seeing flight, the Hughes 369D sustained a loss of engine power, descended, and landed hard on rough/rocky terrain. An exam of the engine revealed the fuel nozzle strainer was contaminated and blocked with sodium, and it was partially collapsed. Tests of the nozzle revealed that flow rates were below the manufacturer's specifications. The helicopter was being operated exclusively in a marine environment and the operator performed compressor wash procedures on a daily basis. In a service letter, the engine manufacturer prescribed turbine engine compressor wash procedures which resulted in immersion of the fuel nozzle in contaminated wash water. There was evidence of subsequent infiltration of wash water into the fuel nozzle strainer. The fuel nozzle strainer had a life limit of 2500 hours, but according to the manufacturer, it was not subject to any prior routine inspection requirement.

History of flight

On April 18, 1994, at 1314 hours Hawaii standard time, a Hughes 369D, N1103N, lost power while maneuvering and collided with rocky terrain below the Manawaupuna Falls, located about 7 miles northeast of Hanapepe, Kauai, Hawaii. The helicopter was being operated by Smoky Mountain Helicopters, Inc., dba Inter-Island Helicopters, Hanapepe, Hawaii, as a sightseeing flight under 14 CFR Part 91. The helicopter was destroyed. The certificated commercial pilot and three passengers were seriously injured. One passenger was fatally injured. The local flight originated at the Port Allen Airport, Hanapepe, Hawaii at 1135 hours. Visual meteorological conditions prevailed.

The helicopter was maneuvering about 150 feet above the surface of a man-made pond below the waterfalls when the engine lost power. The pond was in a valley formed by the Hanapepe River. The surrounding terrain was mountainous covered with thick vegetation.

The pilot stated he noticed a drop in "N2" with an immediate descent. The pilot attempted to fly out of the descent and increased the collective. The pilot stated he then transmitted a Mayday call and "informed the passengers a crash was eminent." The pilot flared the helicopter at treetop level and applied initial cushioning pitch approximately 5 feet above the ground. The pilot stated he did not observe any warning or caution lights during the accident.

The helicopter landed hard in the rocky riverbed about 300 feet downstream from the dam of the man-made pond. All the survivors reported losing consciousness and could not give clear accounts of the circumstances during postaccident interviews.

Personnel information

The pilot holds a Commercial Pilot Certificate with a Rotorcraft- Helicopter rating. According to the operator's accident report, the pilot's total aeronautical experience consists of about 3,100 hours, all of which were accrued in helicopters.

Aircraft information

The helicopter, a Hughes 369D, had accumulated a total time in service of 7,154.3 hours. Examination of the maintenance records revealed that the most recent 100-hour inspection was accomplished on April 14, 1994, 14.3 hours before the accident.

An Allison 250-C20B turboshaft engine, serial number CAE-834267, was removed from the airframe by the operator on January 1, 1994, at 7,322.5 hours total engine time, and later installed in the airframe by the operator on January 28, 1994. The operator's maintenance records indicated about 227.8 hours were flown on the engine after the installation. The engine had accrued a total time in service of 7,550.3 hours at the time of the accident.

According to a statement from the operator, he performs acompressor wash on a daily basis in accordance with theinstructions contained in Allison Service Letter CSL-1135. The procedure was timed at 31 seconds, and 2.5 quarts of water are sprayed into the engine during the process.

Wreckage and impact information

The initial impact point was about 10 feet upstream from the helicopter's point of rest. The landing gear was broken and portions were found upstream with aluminum transferred to submerged rocks.

The belly was crushed upward. The sheet metal was torn from the left side under the pilot's seat aft to the cabin. The cabin floor was displaced upward about 3 inches. The rear seat passenger seatbelt center attach point was torn loose from the aft cabin bulkhead.

The pilot's seat pan was bent downward. The collective torque tube under the pilot's seat was deformed in the same manner contouring the seat pan. The throttle linkage that runs through the collective torque tube was bent corresponding to the seat pan and found in the off position.

The engine turbine section was broken from the accessory gearbox and the fuel control unit was damaged. The engine fuel filter housing was found broken and the filter was found lying on the ground.

The helicopter's fuel cell was found shredded from underneath. No fuel was found in the cells. There was an aroma of jet fuel in the accident area and fuel was noted floating on the water in stagnant pools. One passenger complained of minor skin injuries due to exposure to fuel after the accident. The right rear passenger's seatbelt was found to have jet fuel on it.

The tail boom was severed from the airframe and found about 20 feet downstream in trees on the west bank of the stream. One of the helicopters main rotor blades was found separated and came to rest near the tail boom.

The tail rotor gear box was found attached to the tail boom with about 10 inches of the tail rotor blades broken off. Both outboard segments of the tail rotor blades were found in the accident area. One blade was found about 75 feet downstream of the fuselage. The other blade was found about 100 feet away from the fuselage in vegetation on the east bank of the stream.

Flight control and drive train continuity was established. According to the helicopter airframe manufacturer, the breaks in the drive train and flight controls were consistent with damage generated from impact with the ground.

Tests and research

Engine Examination

The helicopter's engine was examined at the operator's facilities in Hanapepe, Hawaii, on April 21, 1994. There was no evidence or damage found in the engine compressor or turbine section that indicated there was a mechanical failure or malfunction with the rotating or stationary parts.

Fuel Control Inlet Filter

The fuel control inlet filter was tested at Allied Signal Controls and Accessories Division, Burbank, California, on June 1, 1994. The inlet filter was visually inspected and placed in a test fuel control. Metered amounts of fuel were introduced to the fuel control and differential pressures were measured across the control filter. The differential pressures were also measured from randomly selected fuel control inlet filters. The results of the test are attached to this report.

Fuel Spray Nozzle Assembly Flow Tests

The fuel spray nozzle assembly (P/N 6890917, serial No. AG83474) from the accident helicopter was tested on a flow bench at Helipower Services, Santa Paula, California, on June 15, 1994. The nozzle fuel strainer appeared to be collapsed when examined through the fuel inlet end. The nozzle assembly did not meet the flow limits published in the Allison 250-C20 overhaul manual. The tests measure fuel flow in pounds per hour at various specified inlet pressures (PSI). The following table depicts the test results.

Inlet Minimum Maximum Accident Pressure Flow Limit Flow limit Nozzle Flow

60 PSI 23 lb/hr 30 lb/hr 20 lb/hr 125 PSI 50 lb/hr 70 lb/hr 38 lb/hr 200 PSI 138 lb/hr 178 lb/hr 52 lb/hr 400 PSI 260 lb/hr 305 lb/hr 80 lb/hr

After the tests, the fuel nozzle was disassembled and the internal 229 micron fuel strainer was found contaminated and collapsed.

Fuel Filter Information/Research

The helicopter's airframe fuel filter, fuel control unit filter, and fuel nozzle filters are constructed of various micron mesh values. The progression of the filtration runs from fine to course with the 5 micron airframe filter being the finer of the three and the 229 micron fuel nozzle filter being the courser. The fuel control filter is rated at 64 micron. The fuel nozzle filter is final stage of fuel filtration before the fuel enters the combuster section of the engine and is ignited.

The engine manufacturer has established a time limit on the fuel nozzle of 2,500 hours, after which the nozzle must be overhauled. The fuel nozzle screen is not inspected by operators as part of any recurring inspection program approved by the engine manufacturer.

Fuel Filter Examination

The three fuel filters were submitted to Fowler, Inc., Gardena, California, for analy