Narrative:

After takeoff from dtw we were told to maintain 250 KTS and to climb to 13000'. Passing through 10000' I selected 250 KTS on the autoplt 'speed select'. The indication on the FCU (flight control unit) showed that selected speed of 250 KTS would be maintained, however the aircraft continued to accelerate as if it were still in 'managed' speed. It continued to accelerate. When we got the overspd warning the autoplt kicked off. In trying to determine what was happening with the autoplt/autothrust system the aircraft was allowed to climb to 13700'. I disconnected the autothrottles and pulled the power off and descended back to 13000'. The autoplt was reconnected as were the autothrottles and everything worked O.K. Even at a selected speed of 250 KTS. We were then given 16000' as an altitude and when a 'level change' was made everything worked normal. I still don't know what the problem was unless the autothrust system was not active and we had no indication that it was not engaged. It should have been engaged or some indication that it wasn't engaged. This was only my second trip on the large transport after my initial chkout and it came after being off for 2 weeks. However, the first officer and I discussed the situation and neither of us knows why the autothrust system did not respond properly. I did notice that the extreme left hand column on the FMA was blank but in the confusion failed to notice in the far right hand column of the FMA whether the autothrust was engaged. I asked the first officer if he could have accidentally disconnected the autothrust when I asked him to engage the autoplt when we left 3000' AGL since the autothrust engage/disengage pushbutton is right next to the autoplt pushbutton. He said 'he didn't think so'. This whole incident probably would not have happened if I had been more observant of the FMA (flight mode annunciator) indications.

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Original NASA ASRS Text

Title: ACR ADVANCE COCKPIT LGT OVERSHOOTS ALT BY 700' DURING CLIMB, PARTLY AS A RESULT OF AUTOTHROTTLE MALFUNCTION.

Narrative: AFTER TKOF FROM DTW WE WERE TOLD TO MAINTAIN 250 KTS AND TO CLB TO 13000'. PASSING THROUGH 10000' I SELECTED 250 KTS ON THE AUTOPLT 'SPD SELECT'. THE INDICATION ON THE FCU (FLT CTL UNIT) SHOWED THAT SELECTED SPD OF 250 KTS WOULD BE MAINTAINED, HOWEVER THE ACFT CONTINUED TO ACCELERATE AS IF IT WERE STILL IN 'MANAGED' SPD. IT CONTINUED TO ACCELERATE. WHEN WE GOT THE OVERSPD WARNING THE AUTOPLT KICKED OFF. IN TRYING TO DETERMINE WHAT WAS HAPPENING WITH THE AUTOPLT/AUTOTHRUST SYS THE ACFT WAS ALLOWED TO CLB TO 13700'. I DISCONNECTED THE AUTOTHROTTLES AND PULLED THE PWR OFF AND DSNDED BACK TO 13000'. THE AUTOPLT WAS RECONNECTED AS WERE THE AUTOTHROTTLES AND EVERYTHING WORKED O.K. EVEN AT A SELECTED SPD OF 250 KTS. WE WERE THEN GIVEN 16000' AS AN ALT AND WHEN A 'LEVEL CHANGE' WAS MADE EVERYTHING WORKED NORMAL. I STILL DON'T KNOW WHAT THE PROB WAS UNLESS THE AUTOTHRUST SYS WAS NOT ACTIVE AND WE HAD NO INDICATION THAT IT WAS NOT ENGAGED. IT SHOULD HAVE BEEN ENGAGED OR SOME INDICATION THAT IT WASN'T ENGAGED. THIS WAS ONLY MY SECOND TRIP ON THE LGT AFTER MY INITIAL CHKOUT AND IT CAME AFTER BEING OFF FOR 2 WKS. HOWEVER, THE F/O AND I DISCUSSED THE SITUATION AND NEITHER OF US KNOWS WHY THE AUTOTHRUST SYS DID NOT RESPOND PROPERLY. I DID NOTICE THAT THE EXTREME LEFT HAND COLUMN ON THE FMA WAS BLANK BUT IN THE CONFUSION FAILED TO NOTICE IN THE FAR RIGHT HAND COLUMN OF THE FMA WHETHER THE AUTOTHRUST WAS ENGAGED. I ASKED THE F/O IF HE COULD HAVE ACCIDENTALLY DISCONNECTED THE AUTOTHRUST WHEN I ASKED HIM TO ENGAGE THE AUTOPLT WHEN WE LEFT 3000' AGL SINCE THE AUTOTHRUST ENGAGE/DISENGAGE PUSHBUTTON IS RIGHT NEXT TO THE AUTOPLT PUSHBUTTON. HE SAID 'HE DIDN'T THINK SO'. THIS WHOLE INCIDENT PROBABLY WOULD NOT HAVE HAPPENED IF I HAD BEEN MORE OBSERVANT OF THE FMA (FLT MODE ANNUNCIATOR) INDICATIONS.

Data retrieved from NASA's ASRS site as of July 2007 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.