MLG HAS STALL WARNING ACTIVATE ON ROTATION.

Narrative

ON ROTATION ON RWY 23 DSM. THE ACFT STALL WARNING WENT OFF. I VERIFIED THAT AIRSPD WAS INCREASING. HYD PUMPS WERE ON; AND FLAPS WERE AT THE PROPER POS FOR THE RWY 15. I ASKED THE CAPT IF THE ACFT WAS FLYING PROPERLY AND HE STATED IT WAS. HE IMMEDIATELY APPLIED FULL PWR; AND COMMANDED I PULL THE STALL WARNING BREAKERS. THE BREAKERS WERE PULLED IN ACCORDANCE WITH THE FLT HANDBOOK ABNORMAL PROCS. WE WERE SLOW IN SWITCHING TO DEP CTL (THAT MAY JUST HAVE BEEN MY IMPRESSION); BUT NOTHING WAS SAID TO US BY ATC. FLAPS WERE RETRACTED CLOSE TO THEIR MAX ALLOWABLE EXTEND SPD BUT NO LIMITS WERE EXCEEDED. THE FLT WAS ROUTINE FROM THERE ON. AT OUR DEST WE DISCOVERED THE REASON FOR THE WARNING. THE JETWAY IN DSM HAD COME IN CONTACT WITH THE L ANGLE OF ATTACK INDICATOR DEFORMING IT TO FLUSH WITH THE FUSELAGE. WHEN I WALKED AROUND THE ACFT I DID NOT NOTICE THIS SINCE THE LARGE RUBBER BUMPER ON THE JETWAY FLOOR HAD COVERED UP THE DAMAGE. ANOTHER REASON I BELIEVE I MISSED IT WAS THAT ALL OF OUR OTHER DC9'S HAVE ONLY 1 ANGLE OF ATTACK INDICATOR ON THE R SIDE OF THE ACFT. WE HAVE A FEW DC-50 MODEL ACFT THEY HAVE 2; 1 ON EACH SIDE OF THE ACFT. ON PREFLT THE ONE ON THE R SIDE WAS IN THE PROPER POS AND FREE TO MOVE. I GUESS I WILL BE CHKING THESE VERY CLOSELY FOR THE REST OF MY CAREER.