QUSED WITH DISPLAY UNIT NSN 6610-01-147-8346 TO MAKE UP THE VSD-DU; REPLACES 6610-01-255-1321; THIS ITEM HAS CONVERSIONS CHANGING THE INSTRUMENT LANDING SYSTEM DISPLAY PRESENTATION BY DELETING THE PREVIOUS ILS BOX AND REPLACING IT WITH A LOCALIZER AND GLIDE SLOPE RAW DATA DEVIATION SCALE; A NEW ILS/AILA MODE IS CREATED AND THE STEERING CROSS GAIN IS CHANGED; CONVERSION IS IMPLEMENTED BY CHANGING THE DEU FIRMWARE ON THE A23 CCA AND CHANGING THE GENERATOR PROM ON ALL CCA