FLC OF AN ACR MLG ACFT OVERSHOT THEIR ASSIGNED APCH ALT DUE TO A MISUNDERSTANDING OF NEW ROUTING CLRNC.

Narrative

DAY VFR; VERY SHORT LEG CSG-ATL (20 MINS). AIR CREW HAD FLOWN TO CSG THE PREVIOUS NIGHT -- HAD NEVER BEEN TO CSG BEFORE. ACFT WAS AN MLG BASIC WITH AN AUTOPLT (ALT HOLD WAS MCO'ED INOP). COPLT WAS FLYING AND CAPT WAS WORKING THE RADIOS. ON TKOF; FLT WAS CLRED TO 10000 FT. DEP CTL HAD US ON A HDG OF 350 DEGS. PASSING ABOUT 8000 FT DEP CTL INSTRUCTED FLT TO FLY PRESENT HDG TO INTERCEPT V241 TO TIROE; THEN AS FILED AND ALSO A FREQ CHANGE. THE CAPT QUESTIONED THE HDG; KNOWING THAT THE 339 DEG COURSE OF V321 COULDN'T BE INTERCEPTED ON A HDG OF 350 DEGS. MUCH CONFUSION AND DISCUSSION ENSUED; WITH THE CTLR AND EACH OTHER WHICH DISTRACTED BOTH PLTS FROM HEARING THE ALT WARNING HORN. THE COMMAND BARS OF THIS MLG'S AUTOPLT/FLT DIRECTOR MUST BE MANUALLY ADJUSTED IN PITCH AND DO NOT COMMAND A LEVEL OFF AS DO 90 PERCENT OF THE FLEET. WHEN WARNING HORN SOUNDED AGAIN THE ACFT WAS APCHING 11000 FT. THE CREW IMMEDIATELY DSNDED TO 10000 FT BUT WAS REMINDED BY THE CTLR WHEN PASSING THROUGH 10400 FT. UPON ARR IN ATL THE CAPT PHONED THE CTLR AND A POSITIVE AND PRODUCTIVE CONVERSATION TOOK PLACE. SUGGEST THAT THIS POSSIBLE CHANGE OF ROUTING BE MENTIONED IN THE FLT PLAN OR THAT CTLRS BE SURE TO ADVISE AIR CREWS THAT INSTRUCTIONS ARE A NEW CLRNC OR THAT A NEW ONE IS ABOUT TO BE ISSUED.