A B727-200 FOLLOWS A FALSE GS INDUCED BY A PARKED B747 TOO NEAR THE APCH END OF RWY 17C AT DFW; TX.

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INTERCEPTED 20 NM FINAL RWY 17C DFW. AT 4000 FT AND 12 NM OUT WE CAPTURED FALSE GS. FO FLYING AND DSNDED WELL BELOW GLIDE PATH. CORRECTED BY VASI AND NORMAL LNDG. CONDITIONS WERE VFR AND NOTICED B747 HOLDING SHORT ON E SIDE OF RWY 17C. POSSIBLE DISRUPTION OF GS SIGNAL. I BELIEVE NO ACFT SHOULD HOLD SHORT SO CLOSE TO THE ANTENNA. COULD HAVE BEEN HAZARDOUS IFR EVEN IF UNPROTECTED AT 800 FT AND 2 MI VISIBILITY. ATC HAD NO IDEA OF THE POSSIBLE HAZARD AND DID NOT NOTIFY APCHING ACFT UNTIL THE COMPLAINTS STARTED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: CAPT STATED THAT THE PROB WITH THE GS WAS DISCOVERED WHEN THE CREW NOTED THE ALTDEV VIA THE VASI LIGHTS ON RWY 17C. THEY DIDN'T HAVE TIME; DUE TO FREQ CONGESTION; TO COMPLAIN TO THE TWR UNTIL AFTER THEY WERE ON THE GND AND OTHER FLTS BEGAN COMPLAINING. THEY CALLED IN AND AGREED WITH THE COMMENTS ON FREQ. THE B747 WAS RIGHT UP TO THE RWY HOLD SHORT LINE. RPTR BELIEVES THAT 800 FT AND 2 MI ARE THE LIMITS WHERE ATC STARTS PROTECTING THE ILS GS XMITTER BY HAVING ACFT HOLD FURTHER BACK.