AN ACR MD88 FLC DEPARTED THEIR ASSIGNED ALT WHEN THE FO INTERPED AN AIRSPD ASSIGNMENT TO BE AN ALT ASSIGNMENT.

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CLBING OUT OF ATL ON DEP CTL FREQ; FO FLYING; CLRED TO 14000 FT. JUST PRIOR TO REACHING 14000 FT; DEP SAID 'SLOW TO 250 KTS.' I READ BACK; 'ROGER; 2-5-0.' I GAVE RADIO CTL TO FO. I TURNED OFF FREQ TO TALK WITH FLT ATTENDANTS ABOUT POSSIBLE ELECTRICAL PROB/EMER. WE WERE EXPERIENCING LIGHT TO MODERATE CHOP IN AND OUT OF CLOUDS AT THE TIME. SINCE I WAS BUSY; FO QUESTIONED DEP ABOUT THE 'CLB TO 2- 5-0' WHICH HE THOUGHT HE HEARD ME READ BACK TO DEP CTL 125.0. DEP SAID 'ROGER.' NOTE: WE WERE HAVING DIFFICULTY COMMUNICATING DUE TO SLIGHT STATIC FROM BEING IN CLOUDS; AND FO WAS FLYING AND TALKING WHILE ENCOUNTERING THE VERY ROUGH AIR. AS WE CLBED THROUGH 15400 FT; DEP CALLED AND SAID WE HAD LEFT OUR ALT AND TO RETURN IMMEDIATELY. NO CONFLICT. HE STOPPED THE CLB ABOUT 16500 FT AND STARTED TO DSND TO 14000 FT. DSNDING THROUGH 14800 FT; DEP SAID; 'CLB IMMEDIATELY TO 16000 FT TO AVOID TFC AT 14000 FT.' (WE PICKED UP TFC AT 14400 FT ON TCASII.) WE CLBED TO 16000 FT. I GOT BACK ON DEP CTL FREQ WHEN FO SIGNALED THAT WE HAD CLBED THROUGH ALT. CONTRIBUTING FACTORS: 1) ATTN TO ELECTRICAL PROB. 2) FLT CONDITIONS. 3) ONLY 1 PLT COMMUNICATING. 4) BAD COMS TURNOVER ON MY PART PRIOR TO GETTING OFF DEP FREQ.