CLEARWATER, FL, USA
N900JE
LEARJET 35A
DURING TAXI UP TO HANGAR UNDER DIRECTION OF LINEMAN AFTER ARRIVAL THE FLT EXPERIENCED LOSS OF HYDRAULIC PRESSURE AND BRAKES. THE PLT COULD NOT ACTIVATE THE EMERGENCY BRAKES PRIOR TO ROLLING INTO THE HANGAR AND COLLIDING WITH TWO ACFT PRIOR TO COMING TO REST. EXAMINATION OF THE ACFT REVEALED THE SPOILERON CONTROL VALVE ASSEMBLY SUFFERED FRACTURE OF A NAS1351-4H-24P SCREW DUE TO HYDROGEN EMBRITTLEMENT CRACKING WHICH CAUSED THE SCREW HEAD TO SEPARATE FROM THE SCREW SHANK. THE SCREW IS ONE OF THREE WHICH RETAINS THE SELECTOR VALVE TO THE MANIFOLD ASSEMBLY. WHEN THE SCREW FAILED THE VALVE BODY SEPARATED ALLOWING LOSS OF ALL USABLE HYDRAULIC FLUID. THE SOURCE OF THE MIGRATING ELEMENTAL HYDROGEN INTO THE FRACTURE AREA COULD NOT BE DETERMINED. THE VALVE ASSEMBLY HAD BEEN INSTALLED IN THE ACFT SINCE MANUFACTURE IN 1977 AND HAD ACCUMULATED 5,642 HOURS. THE VALVE IS MAINTAINED ON CONDITION.
Source: NTSB Aviation Accident Database
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