Narrative:

Tower cleared us for takeoff. I spooled up engine 2 to 40% N1 to make the left turn from E1 onto the runway. I transferred the controls to the first officer (first officer) after we completed the before takeoff checklist. He advanced the thrust levers (tl) evenly toward the toga detent. I noticed a split in the engine N1 indications immediately. I saw engine 1 N1 at about 40%; and engine 2 N1 at the blue carrot (takeoff setting). The first officer immediately reduced the tl's and called reject; which initially confused me because I thought engine 1 just needed a second or 2 to spool up to catch engine 2. This caused me to verbally override the first officer's reject decision. He advanced the tl's once more; resulting in 'tla not toga' EICAS message and master caution. I realized my mistake and called reject. I took the controls and turned off the runway at E3 taxiway. I made an announcement to the passengers and returned to the gate where we swapped airplanes.one obvious lesson: once the tl's are reduced and the takeoff reject call is made; do not change your mind. Turn off the runway and sort out the issue.lesson 2: trust the pilot flying's judgement. The first officer had good reason to reject. What I didn't know at the time was how much yaw he felt immediately after advancing the tl's; because he compensated for it with the rudder. That prompted him to look at the N1 gauges; which revealed a large split. He has a lot of time in this airplane and that takeoff thrust felt very abnormal to him. Lesson 3: I'm in the habit of often transferring controls to the first officer with one engine already spooled at 40% N1 and the other at idle (20% N1). In this case that added to the confusion. From now on I'll transfer controls with the engines at symmetrical thrust. That takes away the initial confusion regarding takeoff thrust settings.

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Original NASA ASRS Text

Title: EMB-170 First Officer detected a strong yawing moment as thrust was advanced for takeoff and called for the reject. The Captain; seeing nothing wrong called for the takeoff to continue. The First Officer advanced the thrust levers; but not to the TOGA detent causing an 'ENG TLA NOT TOGA' message to be displayed and the takeoff rejected.

Narrative: Tower cleared us for takeoff. I spooled up engine 2 to 40% N1 to make the left turn from E1 onto the runway. I transferred the controls to the First Officer (FO) after we completed the before takeoff checklist. He advanced the Thrust Levers (TL) evenly toward the TOGA detent. I noticed a split in the engine N1 indications immediately. I saw engine 1 N1 at about 40%; and engine 2 N1 at the blue carrot (takeoff setting). The FO immediately reduced the TL's and called reject; which initially confused me because I thought engine 1 just needed a second or 2 to spool up to catch engine 2. This caused me to verbally override the FO's reject decision. He advanced the TL's once more; resulting in 'TLA NOT TOGA' EICAS message and master caution. I realized my mistake and called reject. I took the controls and turned off the runway at E3 taxiway. I made an announcement to the passengers and returned to the gate where we swapped airplanes.One obvious lesson: Once the TL's are reduced and the takeoff reject call is made; do not change your mind. Turn off the runway and sort out the issue.Lesson 2: Trust the pilot flying's judgement. The FO had good reason to reject. What I didn't know at the time was how much yaw he felt immediately after advancing the TL's; because he compensated for it with the rudder. That prompted him to look at the N1 gauges; which revealed a large split. He has a lot of time in this airplane and that takeoff thrust felt very abnormal to him. Lesson 3: I'm in the habit of often transferring controls to the FO with one engine already spooled at 40% N1 and the other at idle (20% N1). In this case that added to the confusion. From now on I'll transfer controls with the engines at symmetrical thrust. That takes away the initial confusion regarding takeoff thrust settings.

Data retrieved from NASA's ASRS site 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.