DURING CLBOUT THE FLC OF A BE2H OVERSHOT THEIR ASSIGNED ALT WHEN THEY BECAME DISTRACTED BY THE INFLATION OF A DEICE BOOT AND A PAX QUESTION. DURING THE PF'S CONVERSATION WITH THE PAX; A CLRNC FOR A LOWER ALT HAD BEEN COPIED BY THE COPLT; BUT WAS NOT CONVEYED TO THE PF.

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I DEPARTED MSL IN A BE2H ON A CORPORATE FLT TO PDK. I WAS FLYING WITH A COPLT AND (2) PAX IN BACK. AFTER TKOF AT AROUND 6000 FT; ZME CLRED ME TO FL210. AT AROUND 17000- 18000 FT; I NOTICED THE R WING BOOT WAS INFLATED AND THE PNEUMATIC PRESSURE WAS ON THE RED LINE. (THE AIRPLANE HAD BEEN PARKED OUTSIDE OVERNIGHT IN VERY COLD TEMP; AND APPARENTLY THE VALVES IN THE PNEUMATIC SYS HAD ICE PROBS. THIS PROB CORRECTED ITSELF WITHIN A FEW MINS.) AT ABOUT THIS TIME ONE OF THE PAX HAD A QUESTION AND I REMOVED MY HEADSET TO ANSWER THEM. WHILE MY HEADSET WAS REMOVED; CTR CHANGED OUR ASSIGNED ALT TO FL200 FOR XING TFC. THE COPLT ACKNOWLEDGED THE ALT AND CHANGED THE ALT IN THE ALT PRE- SELECT WINDOW. AT THIS TIME MY HEADSET WENT BACK ON. I DIDN'T HEAR THE ALT CHANGE; AND DIDN'T SEE THE NEW SETTING IN THE WINDOW. THE COPLT THOUGHT I WAS AWARE OF THE ALT CHANGE AND WE WENT BACK TO DISCUSSING THE PROB WITH THE WING BOOT. AT 20600 FT; ZME INSTRUCTED ME TO DSND BACK TO FL200 IMMEDIATELY. I ACKNOWLEDGED AND DID SO AS RAPIDLY AS POSSIBLE. AT THAT POINT I DISCOVERED THE ASSIGNED ALT WAS FL200; NOT FL210. I WAS IN VMC CONDITIONS AT THE TIME AND SAW THE XING TFC AHEAD AND ABOVE US. I ESTIMATE BTWN 1 AND 2 MI. CTR ASKED OUR ASSIGNED ALT AND THE COPLT ACKNOWLEDGED FL200. WE WERE GIVEN A PHONE NUMBER AT ZME TO CALL LATER. I TALKED WITH CTR PERSONNEL UPON LNDG. I EXPLAINED WHAT HAPPENED AS BEST I COULD. HE INFORMED ME THAT THE INCIDENT WOULD HAVE TO BE TURNED OVER TO FLT STANDARDS OFFICE IN BHM BECAUSE THE OEDP ALARM HAD WENT OFF ON THEIR RADAR COMPUTER. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR HAS RECEIVED TELEPHONE QUESTIONING FROM THE FAA. HE TOLD THEM THAT THE GREATEST CONTRIBUTOR TO THE INCIDENT WAS A FLC COMS BREAKDOWN; BUT THAT THE DEICE SYS PROB GOT THE BALL ROLLING.