Narrative:

Mdw; rejected takeoff runway 31C. After being cleared for takeoff; taxied onto runway 31C. While turning right to centerline; pushed up throttles at 1 inch. Aligned with centerline; rolling down runway and stabilized; pushed throttles up for takeoff. Aircraft immediately turned right. Crosschecked N1's and noticed large split --#1 near takeoff setting and #2 at 40-50%. Tried to correct to centerline (while #2 continued to slowly spool) using rudder then yoke/nosewheel steering. Aircraft did not respond and continued right toward edge of runway. Pulled throttles to idle and used differential braking to correct aircraft to runway centerline. Completed rejected takeoff procedures; informed tower; and was able to easily clear runway; using nosewheel steering; at taxiway K. Obtained clearance from ground control to return to gate. Communicated problem/situation to flight attendants; operations; maintenance and passenger. Maintenance met aircraft at gate and debriefed. In coordination with dispatch; mdw maintenance and maintenance control; elected to pull aircraft 'off line' to inspect nosewheel and run #2 engine. Offloaded passenger. Dispatch assigned new aircraft number and departed 2 hours late. I believe #1 engine spooled much faster than #2. Not sure why nosewheel steering would not correct back to centerline. Maybe momentum? I've noticed an increased number of engines not spooling evenly; especially -300's and early -700's. In the future; I plan to more cautiously push throttles for takeoff thrust and hopefully avoid another above situation. Supplemental information from acn 668565: I would like to recommend that this type of situation be included in simulator training.

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Original NASA ASRS Text

Title: FLT CREW OF B737-700 EXPERIENCE UNEVEN SPOOL-UP OF ENGS ON TKOF FROM MDW. NEARLY RESULTS IN A RWY EXCURSION.

Narrative: MDW; REJECTED TKOF RWY 31C. AFTER BEING CLRED FOR TKOF; TAXIED ONTO RWY 31C. WHILE TURNING R TO CTRLINE; PUSHED UP THROTTLES AT 1 INCH. ALIGNED WITH CTRLINE; ROLLING DOWN RWY AND STABILIZED; PUSHED THROTTLES UP FOR TKOF. ACFT IMMEDIATELY TURNED R. XCHKED N1'S AND NOTICED LARGE SPLIT --#1 NEAR TKOF SETTING AND #2 AT 40-50%. TRIED TO CORRECT TO CTRLINE (WHILE #2 CONTINUED TO SLOWLY SPOOL) USING RUDDER THEN YOKE/NOSEWHEEL STEERING. ACFT DID NOT RESPOND AND CONTINUED R TOWARD EDGE OF RWY. PULLED THROTTLES TO IDLE AND USED DIFFERENTIAL BRAKING TO CORRECT ACFT TO RWY CTRLINE. COMPLETED REJECTED TKOF PROCS; INFORMED TWR; AND WAS ABLE TO EASILY CLR RWY; USING NOSEWHEEL STEERING; AT TXWY K. OBTAINED CLRNC FROM GND CTL TO RETURN TO GATE. COMMUNICATED PROB/SIT TO FLT ATTENDANTS; OPS; MAINT AND PAX. MAINT MET ACFT AT GATE AND DEBRIEFED. IN COORD WITH DISPATCH; MDW MAINT AND MAINT CTL; ELECTED TO PULL ACFT 'OFF LINE' TO INSPECT NOSEWHEEL AND RUN #2 ENG. OFFLOADED PAX. DISPATCH ASSIGNED NEW ACFT NUMBER AND DEPARTED 2 HRS LATE. I BELIEVE #1 ENG SPOOLED MUCH FASTER THAN #2. NOT SURE WHY NOSEWHEEL STEERING WOULD NOT CORRECT BACK TO CTRLINE. MAYBE MOMENTUM? I'VE NOTICED AN INCREASED NUMBER OF ENGS NOT SPOOLING EVENLY; ESPECIALLY -300'S AND EARLY -700'S. IN THE FUTURE; I PLAN TO MORE CAUTIOUSLY PUSH THROTTLES FOR TKOF THRUST AND HOPEFULLY AVOID ANOTHER ABOVE SIT. SUPPLEMENTAL INFO FROM ACN 668565: I WOULD LIKE TO RECOMMEND THAT THIS TYPE OF SIT BE INCLUDED IN SIMULATOR TRAINING.

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.