ACFT NAV EQUIP MALFUNCTIONS.

Narrative

THIS WAS AN EFIS EQUIPPED ACFT (DC-9-40) IN HOUSE INGINEERED (EFIS). DURING TRIP IN FROM ICT EFIS EQUIP APPEARED NORMAL. CREW NOTICED DURING HOLDING OVER SHELBYVILLE VOR THAT WHEN NEARING THE VOR; BOTH CDI NEEDLES BECAME ERRATIC BUT THEN CLRED UP (APPROX 10 DME). HOLDING WAS AT FL240. CLRED TO RID THEN TO ILN WHILE DSNDING. PASSED THROUGH MULTIPLE CLOUD LAYERS DURING DSCNT AND PICKED UP TRACE RIME ICE. DSNDED INTO A SOLID LAYER OF CLOUDS AT 8000 FT MSL AND NEVER EXITED CLOUDS UNTIL ARRIVING DAYTON. CONDITIONS IN CLOUDS WERE MODERATE TO SEVERE MIXED ICING. ACQUIRED APPROX 3 TO 3 1/2 INCHES OF ICE IN ABOUT 20 MINS. AT APPROX 4000 FT MSL ON R BASE TO ILS RWY 22 AT ILN; APPROX 18 TO 20 MI OUT; FO RPTED BEING UNABLE TO GET A CONSTANT IDENT ON RWY 22 LOC. DAY GAVE US AN INTERCEPT HDG AND THEN FO IDENTED LOC ON BOTH SIDES. APPROX 15-20 SECONDS AFTER LOC INTERCEPT BOTH CREW MEMBERS BEGAN GETTING MULTIPLE FAILURES OF FLT DIRECTORS; COMPARATOR FLAGS; AND MULTIPLE IU (RED) INDICATORS; FOLLOWED BY TOTAL FAILURES OF ALL NAV EQUIP; INCLUDING ADF'S. WE WERE UNABLE TO OBTAIN A POSITIVE IDENT ON ANY NAV RADIO. SHORTLY THEREAFTER; CAPT WAS GIVEN MISSED APCH INSTRUCTIONS FROM ILN TWR; (RADIO COM WAS VERY SCRATCHY AND POOR). WE THEN SWITCHED TO DAY APCH I DECLARED AN EMER. DAY ADVISED WE WOULD GET AN ASR TO RWY 36 AT DAY. UPON ARRIVING IN DAY; I OBSERVED ON THE COM AND NAV RADIO ANTENNAE APPROX 3 1/2 INCH CHUNKS OF ICE ON THE LEADING EDGE OF ALL ANTENNAE. ICE MAY HAVE BEEN THE PRINCIPAL CAUSE OF THIS INCIDENT BUT OUR EFIS PROGRAM HAS BEEN FRAUGHT WITH PROBS AND THIS PARTICULAR ACFT HAD 3 PREVIOUS WRITE-UPS FOR SIMILAR OR IDENTICAL PROBS WHICH COULD NOT BE DUPLICATED BY MECHS WHILE ACFT WAS ON THE GND.