GA SMA PLT IS ACCUSED OF MAKING AN ALTDEV FOR CHANGING ALT WITHIN AN ASSIGNED ALT BLOCK.

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DEPARTED IFR FROM MOUNT COMFORT ARPT (INDIANAPOLIS); FILED FOR 4000 FT. HVY ICING AT 4000 FT; INDIANAPOLIS CTLR SUGGESTED 5000 FT WOULD BE BETTER AS TOPS WERE BELOW 5000 FT. I CLBED TO 5000 FT; AND WAS IN BTWN LAYERS. HANDED OFF TO GRISSOM APCH; ALL IS WELL BTWN LAYERS. TOPS STARTED TO GET HIGHER; IN AND OUT OF TOPS; GETTING MORE ICE. I CLBED TO 5200 FT AND STOPPED CLB. STILL JUST BELOW TOPS; ASKED GRISSOM FOR A BLOCK BTWN 5000 FT AND 6000 FT. GRISSOM APPROVED THE BLOCK. I THEN MOVED UP TO 5500 FT AND STAYED THERE. HANDED OFF TO CHICAGO CENTER. THE CENTER OPERATOR PROCEEDED TO TELL ME HOW I CLBED WITHOUT PERMISSION AND WHEN ON AN IFR FLT PLAN I COULDN'T DO THAT. AND THAT HE WASN'T SURE IF GRISSOM WAS GOING TO RPT IT OR NOT. I THANKED HIM FOR COMMENTS. SUNDAY 1/XX/92 ON A VFR TRIP TO LOUISVILLE; I OVERFLEW GRISSOM; ASKED FOR THEIR TELEPHONE NUMBER. WHEN I LANDED AT LOUISVILLE I CALLED AND BY LUCK THE SUPVR ON DUTY WAS THE SAME ONE ON DUTY THURSDAY NIGHT. SHE REMEMBERED MY FLT AND SAID SHE DID NOT HAVE ANY PROBLEMS WITH IT AND DID NOT MAKE ANY RPTS. I THANKED HER AND LEFT IT AT THAT. MY MODE C DOES READ OUT ABOUT 150 FT HIGH; WHICH MAY HAVE BEEN PART OF THE PROBLEM WITH CHICAGO CENTER. ALSO THERE IS A DELAY BTWN THE MODE C READOUT FROM THE AIRPLANE AND THE READOUT THE RADAR OPERATOR GETS. THEY SHOULD KNOW THIS; TO THE CENTER CTLR IT MAY HAVE LOOKED LIKE A CONTINUOUS CLB ON HIS READOUT.