Narrative:

While en route at cruise FL390; the autoplt disengaged. I re-engaged the autoplt and then I noticed vsi fluctuations of +/-100 ft; followed by the autoplt disengaging again. Within 10 seconds we received a red stall warning light; stick shakers on both control panels; a stall fail message caution on the ED1 and the pfd was showing full red indication bars on the airspeed tape. I then advised the first officer to call ATC and tell them we are descending to FL360. I descended to FL360 without the autoplt engaged and I leveled at FL360 and re-engaged the autoplt. Once I engaged the autoplt; the aircraft started a climb of 1000/FPM. I then disengaged the autoplt manually and told the first officer to tell ATC we are descending to a lower altitude. ATC gave us FL340 and I descended to FL340; leveled the aircraft; and turned the autoplt back on. Within 1 min of turning the autoplt back on; and level at FL340; the autoplt disengaged and the stall indications returned. I then declared an emergency through the first officer to ATC and told them we were descending to a lower altitude which ended up being FL210. Throughout the descent from FL340 to FL210; the stall indications previously mentioned continued all the way through the descent to approximately FL280. I was in a 3000-4000/FPM descent while the stall indications were occurring. After approximately FL280; the stall indications ceased and I proceeded to descend to FL210 and I engaged the autoplt. Within 10 mins; the autoplt disengaged and due to the high workload; I re-engaged the autoplt and it operated normally throughout the remainder of the flight. Throughout the event the aircraft never felt like it was about to stall even though I was receiving all indications from the stall system that the aircraft was near a stall. While we were in the descent from FL340 to FL210 the first officer and I were communicating with dispatch and ATC to find a suitable diversion airport. Dispatch informed me that ZZZ was suitable; and we had the appropriate plates to divert there. While en route to ZZZ; we reviewed the stall fail checklist and possible aft door open due to the aft good being deferred. We stayed in contact with dispatch and proceeded to ZZZ and landed without incident. We requested crash fire rescue equipment standing by upon landing. Throughout the flight we communicated several times to the flight attendants on our situation and that we were diverting to ZZZ. We told the flight attendants to prepare for an emergency. I made the decision to declare an emergency and divert to ZZZ based on the information I was receiving throughout the event. Once the passenger deplaned and all of the paperwork was completed; the ground crew at ZZZ informed me that all of the carry-on and checked bags were placed in the aft cargo bin. The forward and center bins were empty. Overall; I feel the event possibly occurred due to aft center of gravity or an electrical anomaly associated with the stall system. Or; a combination of the two. Callback conversation with reporter revealed the following information: reporter stated that following this event; a simulator period determined that the only way this event could occur would be for both stall vanes to have failed. A single failure would not give the full stall warning with the speed tape and pfd commands. The reporter's air carrier was not concerned with baggage loading because the weight was not great enough to cause a cg concern.

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Original NASA ASRS Text

Title: A CRJ900 DIVERTED TO A NEARBY ARPT AFTER BOTH ANGLE OF ATTACK STALL VANES FAILED CAUSING A STALL WARNING IN FLT. AN EMER WAS DECLARED.

Narrative: WHILE ENRTE AT CRUISE FL390; THE AUTOPLT DISENGAGED. I RE-ENGAGED THE AUTOPLT AND THEN I NOTICED VSI FLUCTUATIONS OF +/-100 FT; FOLLOWED BY THE AUTOPLT DISENGAGING AGAIN. WITHIN 10 SECONDS WE RECEIVED A RED STALL WARNING LIGHT; STICK SHAKERS ON BOTH CTL PANELS; A STALL FAIL MESSAGE CAUTION ON THE ED1 AND THE PFD WAS SHOWING FULL RED INDICATION BARS ON THE AIRSPD TAPE. I THEN ADVISED THE FO TO CALL ATC AND TELL THEM WE ARE DSNDING TO FL360. I DSNDED TO FL360 WITHOUT THE AUTOPLT ENGAGED AND I LEVELED AT FL360 AND RE-ENGAGED THE AUTOPLT. ONCE I ENGAGED THE AUTOPLT; THE ACFT STARTED A CLB OF 1000/FPM. I THEN DISENGAGED THE AUTOPLT MANUALLY AND TOLD THE FO TO TELL ATC WE ARE DSNDING TO A LOWER ALT. ATC GAVE US FL340 AND I DSNDED TO FL340; LEVELED THE ACFT; AND TURNED THE AUTOPLT BACK ON. WITHIN 1 MIN OF TURNING THE AUTOPLT BACK ON; AND LEVEL AT FL340; THE AUTOPLT DISENGAGED AND THE STALL INDICATIONS RETURNED. I THEN DECLARED AN EMER THROUGH THE FO TO ATC AND TOLD THEM WE WERE DSNDING TO A LOWER ALT WHICH ENDED UP BEING FL210. THROUGHOUT THE DSCNT FROM FL340 TO FL210; THE STALL INDICATIONS PREVIOUSLY MENTIONED CONTINUED ALL THE WAY THROUGH THE DSCNT TO APPROX FL280. I WAS IN A 3000-4000/FPM DSCNT WHILE THE STALL INDICATIONS WERE OCCURRING. AFTER APPROX FL280; THE STALL INDICATIONS CEASED AND I PROCEEDED TO DSND TO FL210 AND I ENGAGED THE AUTOPLT. WITHIN 10 MINS; THE AUTOPLT DISENGAGED AND DUE TO THE HIGH WORKLOAD; I RE-ENGAGED THE AUTOPLT AND IT OPERATED NORMALLY THROUGHOUT THE REMAINDER OF THE FLT. THROUGHOUT THE EVENT THE ACFT NEVER FELT LIKE IT WAS ABOUT TO STALL EVEN THOUGH I WAS RECEIVING ALL INDICATIONS FROM THE STALL SYS THAT THE ACFT WAS NEAR A STALL. WHILE WE WERE IN THE DSCNT FROM FL340 TO FL210 THE FO AND I WERE COMMUNICATING WITH DISPATCH AND ATC TO FIND A SUITABLE DIVERSION ARPT. DISPATCH INFORMED ME THAT ZZZ WAS SUITABLE; AND WE HAD THE APPROPRIATE PLATES TO DIVERT THERE. WHILE ENRTE TO ZZZ; WE REVIEWED THE STALL FAIL CHKLIST AND POSSIBLE AFT DOOR OPEN DUE TO THE AFT GOOD BEING DEFERRED. WE STAYED IN CONTACT WITH DISPATCH AND PROCEEDED TO ZZZ AND LANDED WITHOUT INCIDENT. WE REQUESTED CFR STANDING BY UPON LNDG. THROUGHOUT THE FLT WE COMMUNICATED SEVERAL TIMES TO THE FLT ATTENDANTS ON OUR SITUATION AND THAT WE WERE DIVERTING TO ZZZ. WE TOLD THE FLT ATTENDANTS TO PREPARE FOR AN EMER. I MADE THE DECISION TO DECLARE AN EMER AND DIVERT TO ZZZ BASED ON THE INFO I WAS RECEIVING THROUGHOUT THE EVENT. ONCE THE PAX DEPLANED AND ALL OF THE PAPERWORK WAS COMPLETED; THE GND CREW AT ZZZ INFORMED ME THAT ALL OF THE CARRY-ON AND CHKED BAGS WERE PLACED IN THE AFT CARGO BIN. THE FORWARD AND CTR BINS WERE EMPTY. OVERALL; I FEEL THE EVENT POSSIBLY OCCURRED DUE TO AFT CTR OF GRAVITY OR AN ELECTRICAL ANOMALY ASSOCIATED WITH THE STALL SYS. OR; A COMBINATION OF THE TWO. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THAT FOLLOWING THIS EVENT; A SIMULATOR PERIOD DETERMINED THAT THE ONLY WAY THIS EVENT COULD OCCUR WOULD BE FOR BOTH STALL VANES TO HAVE FAILED. A SINGLE FAILURE WOULD NOT GIVE THE FULL STALL WARNING WITH THE SPEED TAPE AND PFD COMMANDS. THE REPORTER'S ACR WAS NOT CONCERNED WITH BAGGAGE LOADING BECAUSE THE WEIGHT WAS NOT GREAT ENOUGH TO CAUSE A CG CONCERN.

Data retrieved from NASA's ASRS site as of May 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.