Narrative:

It was the first officer's leg from ZZZ. Upon rotation during takeoff with an approximately 15 KT left crosswind; the first officer noticed a significant roll due to unresponsive aileron input for crosswind correction. The first officer recovered by using right aileron and righting the wings. The first officer then told me the ailerons seemed 'sloppy' and asked me to try flying it at approximately 1200 ft AGL. I took control of the aircraft and noticed the same thing. Basically the ailerons felt as though there was a dead band between 4 degrees left and right deflection. Once I continued roll input beyond 4 degrees; the controls then felt more normal; and roll was ctlable beyond the 4 degree point. The aircraft remained in positive control throughout the flight; the ailerons just felt unresponsive in this 4 degree range of motion either side of center. We climbed to 10000 ft and discussed the problem. I checked circuit breakers and did some troubleshooting but could not find a solution to the problem. We then decided to declare an emergency and return to ZZZ. I communicated with the flight attendants; operations and maintenance while the first officer flew. I then took over control of the aircraft and made a normal approach and landing in ZZZ on runway 25. Callback conversation with reporter revealed the following information: reporter stated that the aileron trim actuator was replaced and several days later the aileron ctring bearing was replaced. No further discrepancies were written against the aileron control system.

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Original NASA ASRS Text

Title: A B737-700 CREW EXPERIENCED AN AILERON DEAD BAND BTWN PLUS OR MINUS 0-4 DEGS OF AILERON MOVEMENT. NORMAL INPUT BEYOND 4 DEGS.

Narrative: IT WAS THE FO'S LEG FROM ZZZ. UPON ROTATION DURING TKOF WITH AN APPROX 15 KT L XWIND; THE FO NOTICED A SIGNIFICANT ROLL DUE TO UNRESPONSIVE AILERON INPUT FOR XWIND CORRECTION. THE FO RECOVERED BY USING R AILERON AND RIGHTING THE WINGS. THE FO THEN TOLD ME THE AILERONS SEEMED 'SLOPPY' AND ASKED ME TO TRY FLYING IT AT APPROX 1200 FT AGL. I TOOK CTL OF THE ACFT AND NOTICED THE SAME THING. BASICALLY THE AILERONS FELT AS THOUGH THERE WAS A DEAD BAND BTWN 4 DEGS L AND R DEFLECTION. ONCE I CONTINUED ROLL INPUT BEYOND 4 DEGS; THE CTLS THEN FELT MORE NORMAL; AND ROLL WAS CTLABLE BEYOND THE 4 DEG POINT. THE ACFT REMAINED IN POSITIVE CTL THROUGHOUT THE FLT; THE AILERONS JUST FELT UNRESPONSIVE IN THIS 4 DEG RANGE OF MOTION EITHER SIDE OF CTR. WE CLBED TO 10000 FT AND DISCUSSED THE PROB. I CHKED CIRCUIT BREAKERS AND DID SOME TROUBLESHOOTING BUT COULD NOT FIND A SOLUTION TO THE PROB. WE THEN DECIDED TO DECLARE AN EMER AND RETURN TO ZZZ. I COMMUNICATED WITH THE FLT ATTENDANTS; OPS AND MAINT WHILE THE FO FLEW. I THEN TOOK OVER CTL OF THE ACFT AND MADE A NORMAL APCH AND LNDG IN ZZZ ON RWY 25. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE AILERON TRIM ACTUATOR WAS REPLACED AND SEVERAL DAYS LATER THE AILERON CTRING BEARING WAS REPLACED. NO FURTHER DISCREPANCIES WERE WRITTEN AGAINST THE AILERON CTL SYS.

Data retrieved from NASA's ASRS site as of January 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.