Narrative:

We were cleared for takeoff. It was the copilot's leg and we made a rolling takeoff. Copilot added thrust to approximately 40% N1 as we were lining up on the centerline. At that point; we were approximately 40 KTS when the copilot pushed the throttles towards takeoff thrust and said 'set takeoff thrust.' target N1 was 85.1% N1. I did not see toga illuminate on the FMC and asked if toga had been selected copilot asked me to reset the thrust as the #1 engine was 5-6% below target I pushed toga again and then manually pushed the #1 thrust lever up to match #2 which was 85.1% N1. As I pushed the throttle up; the autothrottle disarmed and in the distraction of the split thrust settings and manually setting the #1 throttle; I did not call '80 KTS; thrust set.' instead; I saw approximately 100 KTS; with #1 at approximately 81.5% N1 and #2 at approximately 85.1% N1. I said '100 KTS; thrust set.' the throttle was full forward at that point. My decision was the engine was producing good thrust (81.5% N1); we did not have an engine failure; engine fire or engine compressor tall or an unsafe condition that would preclude flying (pre-briefed high speed abort items) thus; I determined it was safer to not make a high speed abort and continued the takeoff. Once safely airborne; we informed departure control that we had a slight engine problem and asked for vectors to remain in the local area. I contacted dispatch and maintenance control. Maintenance control said the engine was probably just out of trim and it would be safe to continue. We decided that although the engine was producing usable thrust; since it would not give full power (approximately 4-5% low); the best decision was to return and let maintenance fix the problem. We coordinated with dispatch and ATC to return and I made an uneventful landing. I briefed the flight attendants and passenger on the return. I did not prepare the cabin or declare an emergency since the engine was running fine -- just a bit below normal due to the out-of-trim condition.

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Original NASA ASRS Text

Title: B737 flight crew reports low N1 during takeoff and elects to continue. Once airborne; and after discussing issue with maintenance; the decision is made to return. The engine runs normally throughout the return and landing.

Narrative: We were cleared for takeoff. It was the Copilot's leg and we made a rolling takeoff. Copilot added thrust to approximately 40% N1 as we were lining up on the centerline. At that point; we were approximately 40 KTS when the Copilot pushed the throttles towards takeoff thrust and said 'Set takeoff thrust.' Target N1 was 85.1% N1. I did not see TOGA illuminate on the FMC and asked if TOGA had been selected Copilot asked me to reset the thrust as the #1 engine was 5-6% below target I pushed TOGA again and then manually pushed the #1 thrust lever up to match #2 which was 85.1% N1. As I pushed the throttle up; the autothrottle disarmed and in the distraction of the split thrust settings and manually setting the #1 throttle; I did not call '80 KTS; thrust set.' Instead; I saw approximately 100 KTS; with #1 at approximately 81.5% N1 and #2 at approximately 85.1% N1. I said '100 KTS; thrust set.' The throttle was full forward at that point. My decision was the engine was producing good thrust (81.5% N1); we did not have an engine failure; engine fire or engine compressor tall or an unsafe condition that would preclude flying (pre-briefed high speed abort items) thus; I determined it was safer to not make a high speed abort and continued the takeoff. Once safely airborne; we informed Departure Control that we had a slight engine problem and asked for vectors to remain in the local area. I contacted dispatch and Maintenance Control. Maintenance Control said the engine was probably just out of trim and it would be safe to continue. We decided that although the engine was producing usable thrust; since it would not give full power (approximately 4-5% low); the best decision was to return and let Maintenance fix the problem. We coordinated with Dispatch and ATC to return and I made an uneventful landing. I briefed the Flight Attendants and passenger on the return. I did not prepare the cabin or declare an emergency since the engine was running fine -- just a bit below normal due to the out-of-trim condition.

Data retrieved from NASA's ASRS site as of April 2012 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.