N2785B
MBB BO-105S
THE TWIN ENGINE HELICOPTER WAS IN CRUISE FLIGHT OVER THE GULF OF MEXICO, WHEN IT SUDDENLY PITCHED NOSE DOWN AND DESCENDED UNCONTROLLED TO IMPACT INVERTED INTO THE WATER. IT SANK TO A DEPTH OF APPROXIMATELY 380 FEET. AFTER RECOVERY OF THE HELICOPTER, EXAMINATION REVEALED THAT AN INCORRECT HYDRAULIC SWITCH GUARD HELD THE TEST SWITCH IN THE RESET POSITION, ELECTRICALLY ISOLATING HYDRAULIC SYSTEM NUMBER TWO FROM OPERATION, AND THAT THE HYDRAULIC MODULE WAS IN THE NUMBER 1 SYSTEM. FURTHER INSPECTION AND TESTING FOUND A DEFECTIVE MICRO-SWITCH IN THE OUTBOARD LATERAL GUIDE ASSEMBLY OF THE HYDRAULIC MODULE. ADDITIONALLY, THE OPERATOR HAD NOT COMPLIED WITH A REQUIRED SERVICE BULLETIN FOR THE MODULE.
THE PARTIAL ELECTRICAL FAILURE OF THE MICRO-SWITCH FOR THE OUTBOARD LATERAL GUIDE ASSEMBLY, AND THE INCORRECT GUARD INSTALLED ON THE HYDRAULIC TEST SWITCH, RESULTING IN A TOTAL HYDRAULIC FAILURE. FACTORS WERE: THE INCORRECT INSTALLATION OF THE GUARD BY AN UNKNOWN PERSON, THE FAILURE OF THE COMPANY TO COMPLY WITH THE SPECIFIED SERVICE BULLETIN.
Source: NTSB Aviation Accident Database
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