LAS VEGAS, NV, USA
N1820U
MCDONNELL DOUGLAS DC-10-10
WHILE CLIMBING THRU 35,000 FT FOR A CRUISE ALTITUDE OF 37,000 FT, THE CREW HEARD A LOUD 'THUMP' & THE ACFT DEPRESSURIZED. AS THE CREW DESCENDED TO 11,000 FT, THE CABIN ALTITUDE CLIMBED TO 30,000 FT. THE FLT DIVERTED TO A NEARBY ARPT & SAFELY LANDED. EXAM OF THE ACFT DISCLOSED THAT REPETITIVE PRESSURIZATION CYCLES CAUSED THE INITIATION OF A FATIGUE CRACK & THE RESULTANT RUPTURE OF A FORWARD PRESSURE BULKHEAD. OVER 14 YRS EARLIER, DOUGLAS ISSUED SERVICE BULLETINS ADVISING OPERATORS THAT LEAKS COULD OCCUR IN THE FWD PRESSURE BULKHEAD AREA BECAUSE OF METAL FATIGUE. DOUGLAS RECOMMENDED THAT SPECIFIC CORRECTIVE ACTION BE TAKEN WHICH INVOLVED INSPECTING THE AREA AT 1,500 HOUR INTERVALS OR MAKING PERMANENT STRUCTURAL AIRFRAME MODIFICATIONS. CONTRARY TO THE MAJORITY OF ACFT OPERATORS, UNITED CHOSE NOT TO STRUCTURALLY MODIFY THIS ACFT. RATHER, IT CHOSE TO PERFORM RECURRING VISUAL INSPECTIONS FOR LEAKS IN THE SUSPECT AREA. THE ACFT'S PRESSURE BULKHEAD RUPTURED 1,367 HRS AFTER IT LAST INSPECTION.
RUPTURE OF A FORWARD PRESSURE BULKHEAD BECAUSE OF CYCLICALLY INDUCED METAL FATIGUE. FACTORS WHICH CONTRIBUTED TO THE INCIDENT WERE: THE OPERATOR'S DECISION NOT TO STRUCTURALLY MODIFY ITS AIRPLANE IN ACCORDANCE WITH THE MANUFACTURER'S BUT RATHER TO RELY ON THE MANUFACTURER'S ALTERNATIVE RECOMMENDATION OF PERFORMING REPETITIVE VISUAL INSPECTION IN THE SUSPECT AREA: AND THE OPERATOR'S FAILURE TO UTILIZE AN INSPECTION PROGRAM ADEQUATE TO VISUALLY DETECT CRACK DEVELOPMENT IN A PREVIOUSLY IDENTIFIED SUSPECT AREA.
Source: NTSB Aviation Accident Database
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