CHANGE TO CTLR HANDBOOK DROPS REQUIREMENT FOR VFR CODE DISPLAY.

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UNTIL RECENTLY; UNDER THE PARAGRAPH 5-2-14. CODE MONITOR; OF THE 7110.65; CTLRS WERE REQUIRED TO MONITOR THE BEACON CODES 1200 AND 4000. THIS REQUIREMENT HAS RECENTLY BEEN DROPPED. I BELIEVE THIS NEW POLICY TO BE A SERIOUS ERROR IN JUDGEMENT AND POTENTIALLY A VERY SERIOUS THREAT TO SAFETY. IF A VFR TARGET DISPLAYING A MODE C READOUT IS BELOW THE ALT LIMITS SET AT A PARTICULAR SECTOR; THE TARGET IS NOT DISPLAYED ON THE RADAR SCOPE. WHILE THIS IS FINE AT OR ABOVE FL180 (CLASS A AIRSPACE) IT COULD BE A VERY SERIOUS SAFETY PROB AT 17500 FT AND BELOW. MY RESEARCH INDICATES THAT A PLT HAS NO WAY OF KNOWING IF A XPONDER IS DISPLAYING AN INACCURATE MODE C READOUT UNLESS HE VERIFIES THE READOUT WITH ATC. FOR EXAMPLE; A PLT IS FLYING AT 11500 FT BELIEVING THAT HIS XPONDER IS FUNCTIONING PROPERLY. HOWEVER; HIS MODE C IS INDICATING HIS ALT IS 8500 FT. AT A SECTOR WITH THE ALT LIMITS SET AT 9800 FT THROUGH 24200 FT (AS MOST SECTORS IN ZTL) THE CTLR WOULD NEVER BE AWARE OF THE ACFT. THE COMPUTER; IN EFFECT; VERIFIES A NON-VERIFIED MODE C AND DOES NOT DISPLAY THE ACFT. THEREFORE; THE CTLR CANNOT ISSUE ADVISORIES ON THIS ACFT; WHOSE ALT IS UNKNOWN; TO ANY CONFLICTING TFC. I BELIEVE THAT THE REQUIREMENT TO ENTER THE BEACON CODES 1200 AND 4000 IN THE BEACON LIST OF THE R-SIDE CRD SHOULD BE REINSTATED IMMEDIATELY.