Narrative:

We had just departed runway 31 at ZZZ1; and were executing a right turn out to the east towards ZZZ2. It was to be a short flight of about 13 mins. ATC had cleared us initially to 7000 ft. This altitude was appropriately entered into the FMS guidance system altitude pre-selector prior to departure; and was confirmed by both crew members. I was the PF; and used the flight director to hand-fly the departure. At about 5000 ft I selected autoplt to on; and noted that the altitude in the pre-selector showed 8000 ft. I assumed the first officer had received clearance to that altitude and it did not register immediately that this altitude was different from our original clearance. Abeam the airport and in cruise-climb through 6000 ft (approximately) my first officer announced that he would be off the #1 communication radio while obtaining the ATIS for our destination of ZZZ2. I replied that I had the #1 communication and pointed out quickly that I was in the climb to 8000 ft. He did not respond as he tuned in the second radio. ATC queried us at 7600 ft as to what we were doing; and I replied that we were climbing to 8000 ft as instructed (or so I thought). The controller gave us an immediate turn and descent back to 7000 ft. Lesson learned: pay closer attention to the altitudes that you have been cleared to previously; and don't assume that what is simply in the pre-selector is correct. We determined that although it is unclr who turned the altitude pre-selector knob; it is likely that one of us did so inadvertently while reaching for the heading control knob located adjacent to it. Also; don't assume that the other crew member agrees with your statements if he or she is silent.

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Original NASA ASRS Text

Title: A BE20 INADVERTENTLY TURNED THE ALT ALERTER AND AFTER ENGAGING THE AUTOPLT CLBED TOWARD THE WRONG ALT UNTIL ATC NOTIFIED THEM OF THE ERROR.

Narrative: WE HAD JUST DEPARTED RWY 31 AT ZZZ1; AND WERE EXECUTING A R TURN OUT TO THE E TOWARDS ZZZ2. IT WAS TO BE A SHORT FLT OF ABOUT 13 MINS. ATC HAD CLRED US INITIALLY TO 7000 FT. THIS ALT WAS APPROPRIATELY ENTERED INTO THE FMS GUIDANCE SYS ALT PRE-SELECTOR PRIOR TO DEP; AND WAS CONFIRMED BY BOTH CREW MEMBERS. I WAS THE PF; AND USED THE FLT DIRECTOR TO HAND-FLY THE DEP. AT ABOUT 5000 FT I SELECTED AUTOPLT TO ON; AND NOTED THAT THE ALT IN THE PRE-SELECTOR SHOWED 8000 FT. I ASSUMED THE FO HAD RECEIVED CLRNC TO THAT ALT AND IT DID NOT REGISTER IMMEDIATELY THAT THIS ALT WAS DIFFERENT FROM OUR ORIGINAL CLRNC. ABEAM THE ARPT AND IN CRUISE-CLB THROUGH 6000 FT (APPROX) MY FO ANNOUNCED THAT HE WOULD BE OFF THE #1 COM RADIO WHILE OBTAINING THE ATIS FOR OUR DEST OF ZZZ2. I REPLIED THAT I HAD THE #1 COM AND POINTED OUT QUICKLY THAT I WAS IN THE CLB TO 8000 FT. HE DID NOT RESPOND AS HE TUNED IN THE SECOND RADIO. ATC QUERIED US AT 7600 FT AS TO WHAT WE WERE DOING; AND I REPLIED THAT WE WERE CLBING TO 8000 FT AS INSTRUCTED (OR SO I THOUGHT). THE CTLR GAVE US AN IMMEDIATE TURN AND DSCNT BACK TO 7000 FT. LESSON LEARNED: PAY CLOSER ATTN TO THE ALTS THAT YOU HAVE BEEN CLRED TO PREVIOUSLY; AND DON'T ASSUME THAT WHAT IS SIMPLY IN THE PRE-SELECTOR IS CORRECT. WE DETERMINED THAT ALTHOUGH IT IS UNCLR WHO TURNED THE ALT PRE-SELECTOR KNOB; IT IS LIKELY THAT ONE OF US DID SO INADVERTENTLY WHILE REACHING FOR THE HDG CTL KNOB LOCATED ADJACENT TO IT. ALSO; DON'T ASSUME THAT THE OTHER CREW MEMBER AGREES WITH YOUR STATEMENTS IF HE OR SHE IS SILENT.

Data retrieved from NASA's ASRS site as of January 2009 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.