Narrative:

Departing iah with thunderstorm activity in the area. Departure control leveled us at 11000 ft MSL. We asked for deviations around a small area of clouds (due to emergency airworthiness directive on aircraft type). ATC told us to deviate as necessary then turn direct bpt when able. Questioning this he realized we were destined for hrl and then cleared us radar vectors (170 degrees) for WX. A couple of mins later ATC told us 'turn right 210.' I acknowledged 210 degree heading. First officer asked if it was heading 210 degree or altitude 210. What I thought I heard him ask was '210?' while my head was down looking at and adjusting radar, first officer initiated climb. At 12800 ft MSL, I notice altitude alerter set for 21000 ft. Suddenly realizing we were climbing out of 12800 ft on a 170 degree heading I leveled aircraft. ATC called at this same time and mentioned we were cleared to maintain 11000 ft. He then cleared us to maintain 14000 ft, heading 210 degrees. Possible factors in this occurrence -- aircraft had emergency airworthiness directive requiring us to stay clear of icing. Total air temperature more than 7 degree C at this point. Due to thunderstorms in area we were being vectored away from clear area and away from planned route. Most aircraft being vectored this new route but ATC not telling anyone in advance. Flying with relatively new first officer. First officer and I did not communicate properly to clarify whether clearance was for climb or turn.

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Original NASA ASRS Text

Title: FO CLBED ABOVE ASSIGNED ALT DUE TO MISUNDERSTANDING ATC INSTRUCTIONS TO TURN TO A NEW HDG.

Narrative: DEPARTING IAH WITH TSTM ACTIVITY IN THE AREA. DEP CTL LEVELED US AT 11000 FT MSL. WE ASKED FOR DEVS AROUND A SMALL AREA OF CLOUDS (DUE TO EMER AIRWORTHINESS DIRECTIVE ON ACFT TYPE). ATC TOLD US TO DEVIATE AS NECESSARY THEN TURN DIRECT BPT WHEN ABLE. QUESTIONING THIS HE REALIZED WE WERE DESTINED FOR HRL AND THEN CLRED US RADAR VECTORS (170 DEGS) FOR WX. A COUPLE OF MINS LATER ATC TOLD US 'TURN R 210.' I ACKNOWLEDGED 210 DEG HDG. FO ASKED IF IT WAS HDG 210 DEG OR ALT 210. WHAT I THOUGHT I HEARD HIM ASK WAS '210?' WHILE MY HEAD WAS DOWN LOOKING AT AND ADJUSTING RADAR, FO INITIATED CLB. AT 12800 FT MSL, I NOTICE ALT ALERTER SET FOR 21000 FT. SUDDENLY REALIZING WE WERE CLBING OUT OF 12800 FT ON A 170 DEG HDG I LEVELED ACFT. ATC CALLED AT THIS SAME TIME AND MENTIONED WE WERE CLRED TO MAINTAIN 11000 FT. HE THEN CLRED US TO MAINTAIN 14000 FT, HDG 210 DEGS. POSSIBLE FACTORS IN THIS OCCURRENCE -- ACFT HAD EMER AIRWORTHINESS DIRECTIVE REQUIRING US TO STAY CLR OF ICING. TOTAL AIR TEMP MORE THAN 7 DEG C AT THIS POINT. DUE TO TSTMS IN AREA WE WERE BEING VECTORED AWAY FROM CLR AREA AND AWAY FROM PLANNED RTE. MOST ACFT BEING VECTORED THIS NEW RTE BUT ATC NOT TELLING ANYONE IN ADVANCE. FLYING WITH RELATIVELY NEW FO. FO AND I DID NOT COMMUNICATE PROPERLY TO CLARIFY WHETHER CLRNC WAS FOR CLB OR TURN.

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.