Narrative:

We had a performance issue departing lga. I am a new captain (under 300 hours) and my first officer is a new hire on his third trip off IOE (initial operating experience). As such I was very deliberate in doing the checklist and checked all takeoff data before leaving the ramp. All takeoff data checked ok with a reduced 26 KT power setting and a takeoff power setting of 97% N1. We closed out 1;400 pounds lighter then planned. Once cleared on to position and hold I taxied the aircraft onto the runway; set the parking brake and waited for landing traffic to clear the intersection. Given takeoff clearance I stood the throttles up to 40% N1; waited for them to stabilize; pressed toga; engaging the autothrottle. I then continued to advance the throttle manually for a faster spool up due to the short runway. Satisfied with the engines; I released the brakes and continued the takeoff roll. With about 2;000 ft of runway remaining I still had not reached V1 and vr and was unhappy with my acceleration. I advanced the power manually; reached vr and brought the aircraft into the air. The ILS antennas on the far end of the runway became abnormally large in the windscreen; however we successfully cleared them. I would estimate by inches not feet. Once at a safe altitude I discussed the event with my new first officer and assured him this was not a normal takeoff. I asked what he saw and he pointed out the power setting had only reached 90-91% N1 during the takeoff roll when commanded setting was to be 97%. It is my firm belief that had I not added more power during the last 2;000 ft there would be much more to tell about this story. I am trying to figure out why the autothrottle did not capture the full takeoff power setting. I had confirmed the commanded setting of 97% several times on the FMC takeoff page during taxi out. I watched the power advance but missed the fact it didn't reach the full 97% as I had transitioned most of my attention outside. Now having time to reflect back; in the recent past the flight department issued a message that the autothrottles should be engaged at 40% N1 and let alone to advance the throttle by themselves. It was my understanding this procedure was to allow for a smooth spool up of the engines and lessen pilot workload. Is it possible that the manual advancement of the throttle beyond the 40% may have disrupted the auto throttle logic? If so; an emphasis should be placed on the dangers of this technique.

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Original NASA ASRS Text

Title: B737 Captain reports discovering late in the takeoff roll that the autothrottles have not achieved planned takeoff N1. Thrust is increased and the aircraft barely clears obstacles at the far end of the runway.

Narrative: We had a performance issue departing LGA. I am a new Captain (under 300 hours) and my First Officer is a new hire on his third trip off IOE (Initial Operating Experience). As such I was very deliberate in doing the checklist and checked all takeoff data before leaving the ramp. All takeoff data checked ok with a reduced 26 KT power setting and a takeoff power setting of 97% N1. We closed out 1;400 LBS lighter then planned. Once cleared on to position and hold I taxied the aircraft onto the runway; set the parking brake and waited for landing traffic to clear the intersection. Given takeoff clearance I stood the throttles up to 40% N1; waited for them to stabilize; pressed TOGA; engaging the autothrottle. I then continued to advance the throttle manually for a faster spool up due to the short runway. Satisfied with the engines; I released the brakes and continued the takeoff roll. With about 2;000 FT of runway remaining I still had not reached V1 and Vr and was unhappy with my acceleration. I advanced the power manually; reached Vr and brought the aircraft into the air. The ILS antennas on the far end of the runway became abnormally large in the windscreen; however we successfully cleared them. I would estimate by inches not feet. Once at a safe altitude I discussed the event with my new First Officer and assured him this was not a normal takeoff. I asked what he saw and he pointed out the power setting had only reached 90-91% N1 during the takeoff roll when commanded setting was to be 97%. It is my firm belief that had I not added more power during the last 2;000 FT there would be much more to tell about this story. I am trying to figure out why the autothrottle did not capture the full takeoff power setting. I had confirmed the commanded setting of 97% several times on the FMC takeoff page during taxi out. I watched the power advance but missed the fact it didn't reach the full 97% as I had transitioned most of my attention outside. Now having time to reflect back; in the recent past the Flight Department issued a message that the autothrottles should be engaged at 40% N1 and let alone to advance the throttle by themselves. It was my understanding this procedure was to allow for a smooth spool up of the engines and lessen pilot workload. Is it possible that the manual advancement of the throttle beyond the 40% may have disrupted the auto throttle logic? If so; an emphasis should be placed on the dangers of this technique.

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.