Narrative:

On arrival; I elected to fly a missed approach and declare an emergency due to being virtually unable to make the aircraft turn left safely. The flight had proceeded normally from initial inspection through taxi-out; takeoff; climb; cruise; and during the arrival. No control issues were detected. This included several ATC assigned turns; both with the autoplt engaged and during manual flight. On the downwind portion of the visual approach; ATC instructed us to slow to final approach speed to allow for departing traffic. We were at about 2000 ft; flaps 30 degrees; 160 KTS. Vref speed at our weight was about 125 KTS. I called for flaps 45 degrees; bug vref; and instructed the first officer to keep an eye on airspeed and to inform me if I went below 145 KTS (I wanted a safety margin until we were aligned with the runway). As the flaps came down; I felt an increasing left wing-down rolling moment. I applied right wing-down aileron trim until the aircraft became more stable. I commented to the first officer that 'this is hard' referring to controling the aircraft. At this point we were in place to begin the base-to-final turn. I attempted 2 or 3 times to make the turn. Each time as left aileron was applied; the aircraft felt like it would snap-roll left if anything more than the smallest bank was applied. I leveled the aircraft; called for a missed approach; and performed a mostly normal missed approach. Once the flaps came up (initially to 8 degrees; then up) the aileron control returned to normal. Initially; tower ATC told us to turn to fly the runway heading and to climb and maintain 2000 ft. I was unable to make the left turn due to the control issues; and was occupied with maintaining aircraft control; so I was unable to arrest the climb until we were almost at 3000 ft. We notified tower ATC of this; that we were on a heading of about 360 degrees and at about 3000 ft. We communicated with ATC; declaring an emergency. We explained our control issue and asked for a right traffic straight-in approach. We were given this by ATC and performed a more or less normal landing. On the second approach; flaps 45 degrees was delayed until about 2 mi out when aligned with the runway. As they came down; the left roll tendency again occurred but; as we did not need any large turns and had a right crosswind; the aircraft was ctlable. On the missed approach we were initially unable to comply with the ATC assigned heading and altitude due to the control issues. As soon as possible we informed ATC of this; declared the emergency; and requested and received an amended clearance. We were able to comply with all further clrncs. All the ATC controllers were extremely helpful during the event. During the event CRM worked very well. The first officer did an excellent job of handling the PNF tasks and primary communications. All company procedures were complied within a fairly timely manner. We were very careful to make sure to run all appropriate checklists on the missed approach and second approach and landing. Callback conversation with reporter revealed the following information: reporter stated that the rolling tendency only occurred with flaps 45 selected. No flap asymmetry was detected by the flap system or from crew observation. The cause of the malfunction was unknown; and the reporter is not aware of any similar occurrences in the fleet.

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Original NASA ASRS Text

Title: A LEFT ROLLING MOMENT WAS INDUCED WHEN LANDING FLAPS WERE SELECTED ON A CRJ200. THE FLT CREW CONDUCTED A GAR; DECLARED AN EMER AND RETURNED FOR LNDG.

Narrative: ON ARR; I ELECTED TO FLY A MISSED APCH AND DECLARE AN EMER DUE TO BEING VIRTUALLY UNABLE TO MAKE THE ACFT TURN L SAFELY. THE FLT HAD PROCEEDED NORMALLY FROM INITIAL INSPECTION THROUGH TAXI-OUT; TKOF; CLB; CRUISE; AND DURING THE ARR. NO CTL ISSUES WERE DETECTED. THIS INCLUDED SEVERAL ATC ASSIGNED TURNS; BOTH WITH THE AUTOPLT ENGAGED AND DURING MANUAL FLT. ON THE DOWNWIND PORTION OF THE VISUAL APCH; ATC INSTRUCTED US TO SLOW TO FINAL APCH SPD TO ALLOW FOR DEPARTING TFC. WE WERE AT ABOUT 2000 FT; FLAPS 30 DEGS; 160 KTS. VREF SPD AT OUR WT WAS ABOUT 125 KTS. I CALLED FOR FLAPS 45 DEGS; BUG VREF; AND INSTRUCTED THE FO TO KEEP AN EYE ON AIRSPD AND TO INFORM ME IF I WENT BELOW 145 KTS (I WANTED A SAFETY MARGIN UNTIL WE WERE ALIGNED WITH THE RWY). AS THE FLAPS CAME DOWN; I FELT AN INCREASING L WING-DOWN ROLLING MOMENT. I APPLIED R WING-DOWN AILERON TRIM UNTIL THE ACFT BECAME MORE STABLE. I COMMENTED TO THE FO THAT 'THIS IS HARD' REFERRING TO CTLING THE ACFT. AT THIS POINT WE WERE IN PLACE TO BEGIN THE BASE-TO-FINAL TURN. I ATTEMPTED 2 OR 3 TIMES TO MAKE THE TURN. EACH TIME AS L AILERON WAS APPLIED; THE ACFT FELT LIKE IT WOULD SNAP-ROLL L IF ANYTHING MORE THAN THE SMALLEST BANK WAS APPLIED. I LEVELED THE ACFT; CALLED FOR A MISSED APCH; AND PERFORMED A MOSTLY NORMAL MISSED APCH. ONCE THE FLAPS CAME UP (INITIALLY TO 8 DEGS; THEN UP) THE AILERON CTL RETURNED TO NORMAL. INITIALLY; TWR ATC TOLD US TO TURN TO FLY THE RWY HDG AND TO CLB AND MAINTAIN 2000 FT. I WAS UNABLE TO MAKE THE L TURN DUE TO THE CTL ISSUES; AND WAS OCCUPIED WITH MAINTAINING ACFT CTL; SO I WAS UNABLE TO ARREST THE CLB UNTIL WE WERE ALMOST AT 3000 FT. WE NOTIFIED TWR ATC OF THIS; THAT WE WERE ON A HDG OF ABOUT 360 DEGS AND AT ABOUT 3000 FT. WE COMMUNICATED WITH ATC; DECLARING AN EMER. WE EXPLAINED OUR CTL ISSUE AND ASKED FOR A R TFC STRAIGHT-IN APCH. WE WERE GIVEN THIS BY ATC AND PERFORMED A MORE OR LESS NORMAL LNDG. ON THE SECOND APCH; FLAPS 45 DEGS WAS DELAYED UNTIL ABOUT 2 MI OUT WHEN ALIGNED WITH THE RWY. AS THEY CAME DOWN; THE L ROLL TENDENCY AGAIN OCCURRED BUT; AS WE DID NOT NEED ANY LARGE TURNS AND HAD A R XWIND; THE ACFT WAS CTLABLE. ON THE MISSED APCH WE WERE INITIALLY UNABLE TO COMPLY WITH THE ATC ASSIGNED HDG AND ALT DUE TO THE CTL ISSUES. ASAP WE INFORMED ATC OF THIS; DECLARED THE EMER; AND REQUESTED AND RECEIVED AN AMENDED CLRNC. WE WERE ABLE TO COMPLY WITH ALL FURTHER CLRNCS. ALL THE ATC CTLRS WERE EXTREMELY HELPFUL DURING THE EVENT. DURING THE EVENT CRM WORKED VERY WELL. THE FO DID AN EXCELLENT JOB OF HANDLING THE PNF TASKS AND PRIMARY COMS. ALL COMPANY PROCS WERE COMPLIED WITHIN A FAIRLY TIMELY MANNER. WE WERE VERY CAREFUL TO MAKE SURE TO RUN ALL APPROPRIATE CHKLISTS ON THE MISSED APCH AND SECOND APCH AND LNDG. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THAT THE ROLLING TENDENCY ONLY OCCURRED WITH FLAPS 45 SELECTED. NO FLAP ASYMMETRY WAS DETECTED BY THE FLAP SYSTEM OR FROM CREW OBSERVATION. THE CAUSE OF THE MALFUNCTION WAS UNKNOWN; AND THE REPORTER IS NOT AWARE OF ANY SIMILAR OCCURRENCES IN THE FLEET.

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.