Narrative:

Aircraft was cleared to 12000 ft MSL. Out of 11000 ft, ZME issued traffic at 12 O'clock position and 10 mi. Center advised if we could take a turn to the right or sight the traffic, we could continue the climb. We accepted the turn to the right. When the captain sighted the traffic, center radio was too busy to advise him. However, the captain thought we were cleared to a higher altitude and had continued to climb. The aircraft climbed to 12900 ft before descending back to 12000 ft. Before reaching 12000 ft, center gave us a higher altitude. Probably 2 things could have been done to prevent this from happening: 1) crew should monitor climb closely the last 1000 ft. 2) use the automation system. The captain was hand flying the aircraft at the time. Supplemental information from acn 475879: I turned right, going through 11000 ft and had traffic in sight at the same time. First officer reported 11000 ft for 12000 ft. I was programmed for higher or to keep climbing. At 12000 ft, I looked at altitude in preset window, asked first officer what altitude we were cleared to -- at time we were 12500 ft. First officer said we weren't cleared higher. Climb was stopped and a descent was started. As mistakes like these occur, I wish I knew the answer. One factor was first time to fly with this person as first officer. I guess to prevent this is to fly with regular people or if someone new, be extra careful.

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Original NASA ASRS Text

Title: A CPR FLT CLBS 800 FT ABOVE ITS ASSIGNED ALT WHEN THE CAPT MISINTERPS THAT CTLR'S PHRASEOLOGY AS A CLRNC FOR A HIGHER ALT 20 NM W OF MSL, AL.

Narrative: ACFT WAS CLRED TO 12000 FT MSL. OUT OF 11000 FT, ZME ISSUED TFC AT 12 O'CLOCK POS AND 10 MI. CTR ADVISED IF WE COULD TAKE A TURN TO THE R OR SIGHT THE TFC, WE COULD CONTINUE THE CLB. WE ACCEPTED THE TURN TO THE R. WHEN THE CAPT SIGHTED THE TFC, CTR RADIO WAS TOO BUSY TO ADVISE HIM. HOWEVER, THE CAPT THOUGHT WE WERE CLRED TO A HIGHER ALT AND HAD CONTINUED TO CLB. THE ACFT CLBED TO 12900 FT BEFORE DSNDING BACK TO 12000 FT. BEFORE REACHING 12000 FT, CTR GAVE US A HIGHER ALT. PROBABLY 2 THINGS COULD HAVE BEEN DONE TO PREVENT THIS FROM HAPPENING: 1) CREW SHOULD MONITOR CLB CLOSELY THE LAST 1000 FT. 2) USE THE AUTOMATION SYS. THE CAPT WAS HAND FLYING THE ACFT AT THE TIME. SUPPLEMENTAL INFO FROM ACN 475879: I TURNED R, GOING THROUGH 11000 FT AND HAD TFC IN SIGHT AT THE SAME TIME. FO RPTED 11000 FT FOR 12000 FT. I WAS PROGRAMMED FOR HIGHER OR TO KEEP CLBING. AT 12000 FT, I LOOKED AT ALT IN PRESET WINDOW, ASKED FO WHAT ALT WE WERE CLRED TO -- AT TIME WE WERE 12500 FT. FO SAID WE WEREN'T CLRED HIGHER. CLB WAS STOPPED AND A DSCNT WAS STARTED. AS MISTAKES LIKE THESE OCCUR, I WISH I KNEW THE ANSWER. ONE FACTOR WAS FIRST TIME TO FLY WITH THIS PERSON AS FO. I GUESS TO PREVENT THIS IS TO FLY WITH REGULAR PEOPLE OR IF SOMEONE NEW, BE EXTRA CAREFUL.

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.