NTSB Identification: LAX94FA130.
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Accident occurred Monday, February 21, 1994 in WALNUT CREEK, CA
Probable Cause Approval Date: 05/04/1995
Aircraft: SIKORSKY S-58T, registration: N581BG
Injuries: 3 Fatal.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
THE HELICOPTER WAS OBSERVED FLYING LOW IN A GRADUAL DESCENT OVER A RESIDENTIAL AREA HEADING TOWARD AN OPEN FIELD. WITNESSES SAID THE HELICOPTER NOISE LEVEL WAS QUIET, BUT NOT SOUNDLESS. AT 200 FEET ABOVE THE GROUND, THE HELICOPTER ROLLED LEFT TO AN INVERTED FLIGHT ATTITUDE AND THEN DESCENDED IN A NOSE-DOWN ATTITUDE. WRECKAGE EXAMINATION DID NOT FIND ANY PREIMPACT MECHANICAL FAILURES WITH THE HELICOPTER'S FLIGHT CONTROL OR DRIVE SYSTEMS. SIGNATURES ON THE INTERNAL ROTATING COMPONENTS OF BOTH ENGINES, THE DRIVE SYSTEM, MAIN ROTOR BLADES, AND TAIL ROTOR BLADES WERE INDICATIVE OF LOW RPM. EXAMINATION OF THE ENGINE FUEL SYSTEM REVEALED EVIDENCE OF FOREIGN PARTICLES IN THE FLOW DIVIDER AND FUEL NOZZLES. POSTACCIDENT FUEL SAMPLES FROM THE REFUELING TRUCK WERE TESTED IN A LABORATORY. ACCORDING TO THE LAB REPORT, THE FUEL HAD A TENDENCY TO ABSORB AND RETAIN WATER, AND A PRESENCE OF MICROBIAL CONTAMINATION WAS NOTED. IN ADDITION TO THE LAB TESTS, FUEL SAMPLES FROM THE OPERATORS REFUELING TRUCKS WERE INDEPENDENTLY TESTED WITH WATER DETECTION PASTE AND TESTED POSITIVE FOR WATER.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: Inadequate fuel quality control procedures by the helicopter operator resulting in fuel contamination and a loss of engine power. The pilot's decision to extend the autorotative glide to avoid striking residential homes, which resulted in low main rotor rpm and a subsequent in-flight loss of control, is also causal in this accident. A factor in the accident was the unsuitable nature of the residential area over which the loss of power occurred for a successful forced landing. Full narrative available
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