EMER DECLARED.

Narrative

AT CRUISE ALT; A LARGE BANG OR THUD WAS FELT ON THE ACFT. NO WARNING LIGHTS ILLUMINATED. ALL ENG INSTS WERE NORMAL. I WENT TO BACK TO CHK CARGO AND ALL WAS SECURE. CAPT CALLED CTR AND ASKED IF ANY ACFT WERE IN THE AREA. THERE WASN'T ANY. THE CAPT DECLARED AN EMER; SLOWED TO 250 KTS AND STARTED DSCNT INTO CEDAR RAPIDS. THE LNDG WAS NORMAL; EXCEPT WE DID NOT GET A BLUE THRUST REVERSER LIGHT ON THE L ENG. WE ROLLED OUT TO THE END OF THE RWY AND CLRED THE RWY. FIRE TRUCKS WERE WAITING. WE STOPPED IN THE RUNUP AREA AND ASKED THE FIRE TRUCKS TO SCAN THE ACFT. THEY SAID EVERYTHING LOOKED OK. WE SHUT DOWN THE R ENG AND TAXIED TO PARKING. ON POSTFLT INSPECTION; WE FOUND THE TOP THRUST REVERSER BUCKET ON THE L ENG HANGING UNDER THE EXHAUST FAIRING WITH A LOT OF DAMAGE TO BOTH THRUST REVERSERS. APPARENTLY THE TOP BUCKET INADVERTENTLY DEPLOYED INFLT AND STRUCK THE LOWER BACK OF THE ENG AND LOWER BUCKET STILL STOWED. THERE WAS NO ADVERSE YAW OR ANY INDICATION THIS HAPPENED UNTIL POSTFLT INSPECTION. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR FLIES THE DC9-30. HIS POSTFLT INSPECTION FOUND THAT A BOLT HAD DROPPED OUT OF THE EXTENSION ARM ON THE UPPER CLAM SHELL DOOR. AIR FORCES CAUSED THE DOOR TO GO AFT AND DOWN THROUGH THE ENG EXHAUST DAMAGING THE LOWER CLAMSHELL DOOR. HE DID NOT KNOW IF THE BOLT HAD FAILED OR SIMPLY DISAPPEARED. THE REVERSER UNLOCK LIGHT IS ON THE LOWER DOOR; SO THERE WAS NO INDICATION IN THE COCKPIT OF THIS ANOMALY. THE REVERSER SEEMED TO WORK PROPERLY ON LNDG ROLLOUT. THERE WAS NO YAW EITHER INFLT OR ON THE GND. AS THERE WAS EXTENSIVE DAMAGE TO THE REVERSER MECHANISM; BOTH THE FAA AND NTSB INVESTIGATED THIS. THE RPTR DOES NOT KNOW WHETHER THIS WAS DETERMINED TO BE AN INCIDENT OR ACCIDENT. THE RPTR HAS HEARD OF NO OTHER FAILURES OF THIS TYPE.