On December 22, 1993, a Hughes 369D (registration N115HD) operated by Smokey Mountain Helicopters was involved in an aviation accident near Waimea, Kauai, HI. Investigators recorded the probable cause as: AN INADEQUATE ENGINE COMPRESSOR CLEANING PROCEDURE SPECIFIED IN THE MANUFACTURER'S SERVICE LETTER, WHICH RESULTED IN THE TOTAL LOSS OF ENGINE POWER DUE TO CONTAMINATION, BLOCKAGE, AND COLLAPSE OF THE FUEL NOZZLE INLET SCREEN. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During an external load operation, the helicopter's engine lost power. The aircraft performed an autorotation into a riverbed, struck a boulder, and rolled over. Examination revealed a collapsed fuel inlet screen contaminated with sodium-rich silicon material from a daily compressor wash procedure.
Accident Overview
During an external load operation, the helicopter's engine stopped producing power. The pilot executed an autorotation into a river bed area. During the landing, the helicopter contacted a boulder and rolled over.
Investigation and Examination
Engine examination revealed a collapsed fuel inlet screen within the fuel nozzle, which restricted fuel flow. Heavy contamination was noted on the screen. Subsequent analysis identified the contaminant as a sodium-rich silicon material.
Wash Procedure and Contamination
The helicopter was operated exclusively in a marine environment. The operator performed a daily compressor wash procedure in accordance with the engine manufacturer's service letter. The specified procedure resulted in immersion of the fuel nozzle in sodium-contaminated wash water, with subsequent infiltration of the solution into the fuel nozzle inlet screen.
Fuel Nozzle Screen Details
The fuel nozzle inlet screen has a life limit of 2,500 hours and is not subject to any routine inspection requirements.