FLC OF A CPR C550 ON AN NDB APCH HAD TWR INFORM THEM THEY WERE N OF COURSE. AT ABOUT THE SAME TIME THE NEEDLES SWUNG 20 DEGS L INDICATING N OF COURSE.

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CMH APCH CLRED US FOR THE NDB RWY 27L TO OSU. BOTH PLT AND COPLT ADF NEEDLES CONFIRMED WE WERE TRACKING THE INBOUND APCH COURSE OF 276 DEGS UNTIL WE WERE APPROX 2.5 MI FROM THE MISSED APCH POINT. BOTH NEEDLES SUDDENLY SWUNG L ABOUT 20 DEGS; INDICATING WE WERE N OF COURSE. THE OSU TWR THEN STATED THAT WE APPEARED TO BE ABOUT 1 MI N OF COURSE. WE CORRECTED OUR HDG TO REINTERCEPT THE FINAL APCH COURSE AND LANDED WITHOUT INCIDENT. THE TWR ASKED IF WE WERE RECEIVING THE NDB ADEQUATELY AS WE WERE THE SECOND ACFT THAT MORNING TO TRACK INBOUND N OF COURSE. WE RESPONDED THAT THE MORSE CODE SIGNAL WAS CONTINUOUSLY MONITORED. THE TWR SUGGESTED THERE WAS PROBABLY A PROB WITH THE APCH AND THAT THEY WOULD RESEARCH IT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT THE APCH SEEMED FINE UNTIL THEY GOT IN CLOSE AND THE NEEDLE SWUNG. CTLR CONTACTED THEM ONCE ON THE GND TO GET MORE INFO SINCE THIS HAD HAPPENED TO A PREVIOUS FLT AS WELL. THEY HAVE BEEN INTO THE ARPT SINCE THAT TIME BUT USED A DIFFERENT RWY AND DIFFERENT APCH. THE CTLR INDICATED THEY WOULD FOLLOW UP ON THE PROB.