Narrative:

The problem is that something happened and we don't know what happened. I have many thousands of hours flying embraer jets. I know that really doesn't mean anything. I just have to say I never experienced or heard of anything like this. Therefore; I write this report about this instance in the hopes that this event never happens again. If it should happen again; this as soon as possible report exists as the record/history of a problem to be fixed with the embraer jet or procedure. The first officer and I discussed the event once we climbed above 15000 feet. It is important to note that we differ in thought as to exactly the timing of the following event story. We turned the situation inside and out and rolled it over and over. We did agree on one thing. The situation had us both completely baffled. So you get my story; not his; not ours. Timing refers to time/altitude or altitude/time. It is also important to note the following;1. Our inflight discussion was an attempt to figure out what went wrong and where so that we could learn something; despite the fact that we covered/took care of this tem (threat error management) moment; not an attempt to get our story straight. 2. Just like thousands of hours not meaning much; I learned to fly and did so for several hundred hours in/around montana. So; do I have a healthy respect for mountains? Absolutely.it was the BOBKT3 RNAV departure runway 12 bozeman; montana. We were heavy. We were several hundred pounds below the day's maximum takeoff weight for the day's conditions. Up until 500 AGL according to the departure plate; it all seemed normal. In this business tem is everywhere. Even the smallest item missed can cause big problems later. On this day we didn't do a rolling takeoff. There were no issues with the aircraft. Yet; I elected to use the APU to run the environmental system for the takeoff. I set partial power before brake release. Seconds later I moved thrust levers towards the toga position. Autothrottle system grabbed the thrust levers and placed them into the detent position and full no flex power noted as we rolled down the runway. Why didn't I do a rolling T/O? I wasn't about to waste any pavement. The sooner I get airborne; the better the terrain management.I followed the crosshairs as I was climbing and tracking plate course. The tower called out traffic. As I lost the crosshairs I initially transitioned to and began to follow the diamond flight director in climb and track. Engine power always reduces right at this point. Engine power did reduce from the no flex power setting. My body felt the power reduction as we were climbing out in VMC conditions. My ears heard the power change. My peripheral vision noted the thrust levers moving farther than expected. I believe the autothrottle system was reducing engine power/thrust levers to the flight idle position. First officer noticed right away and blocked prior to autothrottle attaining flight idle and pushed thrust levers forward to counter. At the same time as first officer blocked/countered I lowered the pitch attitude of the aircraft to avoid/counter aircraft slow down to reach flap retraction speed and yet continue climbing. The flight director was demanding extra degrees of pitch up. 1 second after first officer blocked; my right hand replaced his on thrust levers. The tower called out traffic. Crossing above 2000 AGL and our first crossing restriction assured; full automation was applied and used for the duration of the flight without any other anomalies noted. The flight was never in danger for a combination of reasons. Very good VMC conditions and good teamwork. I know this all electronic airplane records practically everything. I'm sure there is some sort of algorithm that can be applied to see if this has happened in the past. I'm sure said algorithm can also be applied going forward to catch this anomaly should it ever occur again.

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Original NASA ASRS Text

Title: EMB170 flight crew reported unusual autothrottle operations during takeoff from BZN Runway 12. Shortly after takeoff the thrust levers began reducing toward idle and the First Officer intervened to return thrust to an appropriate setting.

Narrative: The problem is that something happened and we don't know what happened. I have many thousands of hours flying Embraer jets. I know that really doesn't mean anything. I just have to say I never experienced or heard of anything like this. Therefore; I write this report about this instance in the hopes that this event never happens again. If it should happen again; this ASAP report exists as the record/history of a problem to be fixed with the Embraer jet or procedure. The First Officer and I discussed the event once we climbed above 15000 feet. It is important to note that we differ in thought as to exactly the timing of the following event story. We turned the situation inside and out and rolled it over and over. We did agree on one thing. The situation had us both completely baffled. So you get my story; not his; not ours. Timing refers to time/altitude or altitude/time. It is also important to note the following;1. Our inflight discussion was an attempt to figure out what went wrong and where so that we could learn something; despite the fact that we covered/took care of this TEM (Threat Error Management) moment; not an attempt to get our story straight. 2. Just like thousands of hours not meaning much; I learned to fly and did so for several hundred hours in/around Montana. So; do I have a healthy respect for mountains? Absolutely.It was the BOBKT3 RNAV departure runway 12 Bozeman; Montana. We were heavy. We were several hundred pounds below the day's maximum takeoff weight for the day's conditions. Up until 500 AGL according to the departure plate; it all seemed normal. In this business TEM is everywhere. Even the smallest item missed can cause big problems later. On this day we didn't do a rolling takeoff. There were no issues with the aircraft. Yet; I elected to use the APU to run the environmental system for the takeoff. I set partial power before brake release. Seconds later I moved thrust levers towards the TOGA position. Autothrottle system grabbed the thrust levers and placed them into the detent position and full no flex power noted as we rolled down the runway. Why didn't I do a rolling T/O? I wasn't about to waste any pavement. The sooner I get airborne; the better the terrain management.I followed the crosshairs as I was climbing and tracking plate course. The tower called out traffic. As I lost the crosshairs I initially transitioned to and began to follow the diamond flight director in climb and track. Engine power always reduces right at this point. Engine power did reduce from the no flex power setting. My body felt the power reduction as we were climbing out in VMC conditions. My ears heard the power change. My peripheral vision noted the thrust levers moving farther than expected. I believe the autothrottle system was reducing engine power/thrust levers to the flight idle position. First Officer noticed right away and blocked prior to autothrottle attaining flight idle and pushed thrust levers forward to counter. At the same time as FO blocked/countered I lowered the pitch attitude of the aircraft to avoid/counter aircraft slow down to reach flap retraction speed and yet continue climbing. The flight director was demanding extra degrees of pitch up. 1 second after FO blocked; my right hand replaced his on thrust levers. The tower called out traffic. Crossing above 2000 AGL and our first crossing restriction assured; full automation was applied and used for the duration of the flight without any other anomalies noted. The flight was never in danger for a combination of reasons. Very good VMC conditions and good teamwork. I know this all electronic airplane records practically everything. I'm sure there is some sort of algorithm that can be applied to see if this has happened in the past. I'm sure said algorithm can also be applied going forward to catch this anomaly should it ever occur again.

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.