B727 CREW GOT A EGPWS WARNING AT 500-600 FT 2 MI FROM THE END OF RWY 8L AT IAH. CREW FOLLOWED EGPWS PROCS. ON THE SECOND APCH THEY GOT A EGPWS WARNING IN THE SAME PLACE BUT CONTINUED TO AN UNEVENTFUL LNDG.

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THIS TRIP ORIGINATED IN MEMPHIS; TN; AND WAS THE SECOND LEG OF THE TRIP. THE CAPT FLEW THIS LEG AND WAS ASSISTED BY MYSELF; THE FO AND THE FE. TRIP WAS UNEVENTFUL ON TKOF; CLBOUT; ENRTE AND DSCNT. THE ACFT WAS VECTORED TO THE FINAL APCH COURSE OF IAH (ILS LOC RWY 8L) AND FINAL VECTOR AND APCH CLRNC WAS RECEIVED APPROX 15 MI AND 2000 FT MSL. ACFT RESPONDED PROPERLY TO INTERCEPT ANGLE AND LOC AND IBZU WAS IDENTED PROPERLY AND APPEARED TO BE WORKING PROPERLY. AS THE ACFT REACHED THE GS INTERCEPT AND DSCNT FROM 2000 FT MSL WAS INITIATED; THE LOC MAY HAVE MOMENTARILY GONE OFF LINE AND BACK ON AND IN CONJUNCTION; THE GPWS ALSO ACTIVATED A WARNING WHILE THE ACFT WAS JUST BREAKING OUT OF WX. THE CAPT CONFIGURED WITH FO AND FE IF THE CHKLIST WAS COMPLETED (AND ALL CHKLISTS WERE PERFORMED PROPERLY) AND THE ACFT CONFIGN WAS RE-VERIFIED (GEAR DOWN; FLAPS EXTENDED PROPERLY; SPD BRAKES STOWED...ALL IN PROPER CONFIGN). THE CAPT CALLED FOR A MISSED APCH AND WE REQUESTED RE-VECTORING TO THE SAME RWY 8L. WHILE ON DOWNWIND RADAR VECTORS; THE EMER CHKLIST WAS CONSULTED AND WE DISCUSSED POSSIBLE PROBS ASSOCIATED WITH THE NAV AND GPWS SYS. ACFT WAS RE-VECTORED FOR THE SECOND APCH TO ILS RWY 8L; AND CONFIGURED PROPERLY AND INTERCEPTED THE APCH AGAIN NEAR 15 MI. AGAIN; THE GPWS ACTIVATED AT THE SAME GEOGRAPHIC POS AND WE LOOKED OVER THE ACFT CONFIGN AND DETERMINED A SAFE LNDG COULD BE COMPLETED AND WAS DONE. POSSIBLY SOME SOFTWARE PROBS IN THE ACFT SYS OR GND INTERFERENCE MAY HAVE CAUSED THE NAV AND GPWS ANOMALIES/FALSE ACTIVATIONS. AS A PRECAUTION FLT SAFETY RPT SUBMITTED AND ACFT SYS WROTE UP FOR INSPECTION.