FLC OF MLG ACR ACFT EXPERIENCED RADIO TRANSPONDER EQUIP MALFUNCTIONS RESULTING IN BECOMING OFF COURSE AND ATC INTERVENING TO CORRECT THE ACFT'S FLT PATH.

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DEPARTING THE DCA ARPT ON APR/TUE/92 TO THE S; AND DURING CLBOUT; ATC FIRST ADVISED AND RPTED THAT THEY WERE NOT RECEIVING OUR ALT TRANSPONDER READOUT RPT. I THEN RECYCLED OUR TRANSPONDER FROM 'ON' TO 'STANDBY' AND BACK TO 'ON;' THEN SWITCHED FROM '#1 TRANSPONDER' TO '#2 TRANSPONDER;' AND NEXT FROM '#1 ALT RPT' TO '#2 ALT RPT.' AFTER ALL THIS ATC ADVISED THAT OUR TRANSPONDER RPT WAS 'INTERMITTED; BUT THAT WE WERE IN RADAR CONTACT.' AT LEVEL OFF AT 17000 FT; ATC RPTED OUR ALT TRANSPONDER READOUT TO BE '17500 FT' AND ASKED US TO VERIFY OUR ALT. OUR ALT WAS 17000 FT; AND I VERIFIED THIS TO ATC; NEXT SWITCHING FROM TRANSPONDER ALT RPTING SYS FROM #1 TO #2. ATC THEN ADVISED RECEIVING OUR ALT RPT AS 'LEVEL AT 17000 FT.' ON ARR AT OUR DEST CLE; I MADE A LOGBOOK ENTRY FOR OUR TRANSPONDER PROBLEM; AND MAINT FOUND AND CORRECTED A LOOSE ANTENNA CONNECTION ON OUR TRANSPONDER RPTR BOX. ON THIS SAME FLT; MY FO FLYING; WE WERE RECEIVING ATC VECTORS FROM THE DCA DEP CTL; AND THEN HANDED OFF TO ZDC WHILE STILL ON AN ASSIGNED VECTOR HDG FOR WX AVOIDANCE. WHEN THE FO COURSE NEEDLE CTRED ON THE AIRWAY HE TURNED ON COURSE J-111; APPROX 40 DME EMI; ATC CALLED US AND GAVE US A 20 DEG L HDG CHANGE TO REINTERCEPT J-111; RPTING US TO BE OFF COURSE? I THEN MATCHED THE #1 NAV RECEIVER TO THAT OF THE #2 NAV RECEIVER; AND FOUND A 30 DEG DIFFERENCE BTWN THE 2 RECEIVERS. I RPTED THIS TO ATC; GIVING THEM THE INFO WHICH I HAD ON THE INCORRECT RECEPTION OF OUR #2 NAV RECEIVER. ATC NEXT AGAIN GAVE US ANOTHER OFF AIRWAY J-111 HDG TO THE S FOR WX AVOIDANCE AND TFC. WHEN CLR OF WX WE WERE AGAIN CLRED DIRECT TO JST. WHILE PROCEEDING DIRECT TO JST; ATC SHORTLY THEREAFTER GAVE US A 100 DEG L HDG CHANGE TO RETURN TO THE DIRECT COURSE TO JST; ADVISING US THAT WE WERE ABOUT TO ENTER ZNY'S AIRSPACE? FO #2 NAV RECEIVER AGAIN DISPLAYED THE PARTIAL FAIL FLAG (LESS THAN 1/2 THE LOC - VOR FLAG) WITH CDI NEEDLE SLIGHTLY R OF COURSE; CORRECT IDENT AND DME. WHILE PREPARING TO CONTINUE WITH THIS ACFT TO IAH AND PERFORMING THE 'RECEIVING ACFT CHKLIST' AND TUNING UP THE NAV RADIOS; THE FO'S CDI FAIL FLAG AGAIN APPEARED (LESS THAN 1/2 VOR - LOC FLAG SHOWING). MAINT WAS CALLED TO RETURN TO THE ACFT. FO'S CDI WAS WRITTEN UP AGAIN IN THE ACFT LOG; AND MAINT CHANGED OUT THE FO'S CDI DISPLAY. IN MY OPINION WX AND PRECIPITATION DID PLAY A PROBLEM IN NAVING DCA TO J-111; AND FROM EMI TO JST; IN THAT THERE WERE MANY ACFT DEVIATING FOR WX; AND ATC WAS EXTREMELY BUSY. HOWEVER; TWICE I HAD MADE RPTS TO ATC THAT OUR FLT WAS RECEIVING VOR NAV RECEPTION AND INDICATION PROBLEMS; AND I FELL THAT ATC COULD HAVE KEPT A BETTER EYE ON US THAN THEY DID. A 100 DEG HDG CHANGE IS EXTREMELY ALARMING TO ME AS A PLT WHEN GIVEN THE CTLR'S TONE AND PITCH IN HIS VOICE THAT WE WERE ENTERING SOMEONE ELSE'S AIRSPACE? I DO NOT KNOW WHAT I OR MY FO COULD HAVE DONE DIFFERENTLY THAN I HAVE DESCRIBED ABOVE.