MIL C137 CAPT; THINKING HE IS CLRED TO 10000 FT; OVERSHOOTS ASSIGNED ALT OF 11000 FT.

Narrative

ON DSCNT WITH ZID I WAS FLYING THE ACFT FROM THE L SEAT. I RECALLED OUR CLRNC TO 10000 FT. WE WERE DEVIATING FROM NUMEROUS RAIN SHOWERS. THE COPLT RECALLED AN ALT CLRNC TO 11000 FT AND SET THE ALT ALERTER. AFTER MORE DEVS FOR RAIN SHOWERS; I ASKED THE CREW IF WE WERE CLRED TO 10000 FT. THE COPLT WAS ADJUSTING THE WX RADAR AT THIS TIME. THE NAV (THE C137 HAS A 4 PERSON CREW) CONFIRMED 10000 FT; AND I RESET THE ALT ALERTER TO 10000 FT. WE WERE IN A SLIGHT DSCNT WHEN CTR ASKED US FOR OUR ALT. THE COPLT LOOKED OVER AT THE ALT ALERTER AND SEEING 10000 FT; REPLIED PASSING 11000 FT FOR 10000 FT. I LEVELED THE ACFT AT 10600 FT. THE COPLT ASKED CTR 'CONFIRM ALT CLRED TO.' AFTER A SLIGHT DELAY; CTR CLRED US TO 10000 FT. THE JUMP SEAT PLT WAS LISTENING TO ATIS; THE FE WAS ACCOMPLISHING CHKLIST ITEMS DURING THIS. REMAINDER OF THE APCH WAS UNEVENTFUL. RECOMMENDATION: CLARIFYING A CLRNC WITHIN THE COCKPIT DOES NOT ASSURE YOU OF COMPLETELY UNDERSTANDING ATC'S INSTRUCTIONS. AT THE FIRST HINT OF UNCERTAINTY; IT CANNOT BE OVERSTATED -- QUERY THE CTLR -- ESPECIALLY FOR CLRNC OF 11000 FT OR 10000 FT. ADDITIONALLY; IF ATC IS UNSURE IF YOU ARE AT YOUR ASSIGNED ALT; THEY SHOULD FIRST STATE YOUR CLRED ALT IN THE ATC SYS; SO YOU CAN CORRECT IF NECESSARY. ATC ASKING THE CREW FIRST CAN DELAY POSSIBLE CORRECTIVE ACTION.