CHICAGO, IL, USA
N1852U
McDonnell Douglas DC-10-30
SHORTLY AFTER TAKEOFF, THE FLIGHT CREW HEARD A NOISE FROM THE RIGHT SIDE OF THE AIRCRAFT, WHICH SOUNDED LIKE AN ENGINE COMPRESSOR STALL. THE #3 ENGINE WAS SHUT DOWN & THE CREW MADE AN UNEVENTFUL LANDING AT THE DEPARTURE AIRPORT. PIECES OF COWLING FROM THE RIGHT ENGINE FELL IN A RESIDENTIAL AREA, BUT DID NO DAMAGE. TEARDOWN OF THE ENGINE REVEALED THAT TURBINE BLADES ON THE FIRST STAGE LOW PRESSURE TURBINE WHEEL HAD BROKEN OFF & HAD PENETRATED THE ENGINE CASE & CORE COWL DOORS. FURTHER INVESTIGATION REVEALED THAT 2 STUD BOLTS (SADDLE BOLTS) HAD PULLED OUT FROM STRUT BOSSES 2 & 3 IN THE TURBINE MID FRAME (TMF), WHICH PLACED AN ADDITIONAL LOAD ON STRUT BOSSES 1 & 4. EVENTUALLY, THE 1 & 4 SADDLE BOLTS PULLED LOOSE & ALLOWED THE NOZZLE SUPPORT FLANGE TO SHIFT REARWARD. THIS SHIFT ALLOWED THE NOZZLE SEGMENTS TO COME IN CONTACT WITH THE LOW PRESSURE TURBINE & RESULT IN THE FAILURE. THERE WAS INDICATION THAT UNAUTHORIZED REWORK HAD BEEN ACOMPLISHED ON THE SADDLE BOLTS BEFORE OWNER (UNITED AIRLINE) HAD PURCHASED THE AIRPLANE FROM ANOTHER (LAKER) AIRLINE.
Source: NTSB Aviation Accident Database
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