TUCSON, AZ, USA
N198AW
BOEING 737-204
DURING APPROACH, A FIRE ERUPTED IN THE WHEEL WELL OF THE 22-YR OLD AIRPLANE. THE FIRE BURNED THRU THE HYDRAULIC LINES RENDERING THE A, B, & STANDBY HYD SYSTEMS INOP. THE CREW LANDED THE AIRPLANE USING THE EMERGENCY MANUAL REVERSION FLIGHT CONTROL SYSTEM. HOWEVER, THE AIRPLANE WAS UNABLE TO STOP ON THE RUNWAY BECAUSE OF THE PREVIOUS FAILURES OF THE CHECK VALVES IN THE BACKUP HYD ACCUMULATOR PRESSURE SYSTEMS FOR THE #2 THRUST REVERSER AND THE INBOARD PAIR OF WHEEL BRAKES. DURING THE 2 MIN ROLLOUT, THE AIRPLANE TRAVERSED 14,000 FT, OVERRAN THE RWY END, AND COLLIDED WITH A CONCRETE STRUCTURE WHICH COLLAPSED THE NOSE GEAR. THE AIRPLANE HAD RECENTLY UNDERGONE A 'C' CHECK DURING WHICH THE OPERATOR'S MECHANICS FAILED TO OBSERVE & REPAIR AN ELECTRIC WIRE WHICH HAD BEEN CHAFING AGAINST A HYD LINE. ON THE ACCIDENT FLT THE ENERGIZED WIRE ARCED, PUNCTURED THE LINE, & IGNITED THE ESCAPING HYD FLUID. THE HYD CHECK VALVES HAD FAILED EARLIER DUE TO MECHANICAL WEAR.
FAILURE OF THE OPERATOR'S MAINTENANCE PERSONNEL TO DETECT AN ELECTRICAL WIRE WHICH HAD CHAFED AGAINST A HYDRAULIC LINE AND WHICH EVENTUALLY ARCED CAUSING A LEAK IN THE HYDRAULIC LINE AND SUBSEQUENT FIRE AND HYDRAULIC SYSTEM FAILURE. IN ADDITION, PREVIOUS WEAR OF CHECK VALVES IN THE BACKUP HYDRAULIC SYSTEMS PREVENTED THE AIRPLANE FROM STOPPING ON THE RUNWAY. A CONTRIBUTING FACTOR WAS THE AIRPLANE MANUFACTURER'S INADEQUATE GUIDANCE FOR MAINTAINING THE HYDRAULIC COMPONENTS.
Source: NTSB Aviation Accident Database
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