ATX X FALSE GPWS. NON ADHERENCE TO ATC CLRNC. CLB FROM ASSIGNED ALT. PLTDEV.

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ATX X WAS INBOUND TO BTV ON VECTORS FOR THE ILS APCH TO RWY 15. THEY WERE LEVEL AT 5500 15 MI SE OF BTV IN MOUNTAINOUS TERRAIN (CAMEL'S HUMP WAS UNDER THE ACFT 4088 MSL). ATX X WAS OPPOSITE DIRECTION CLBING OUT OF 8000 DIRECTLY OVER ATX X WHEN ATX X ANNOUNCED HE WAS CLBING FOR A GPWS ALARM. I TOLD ATX X THAT HIS ALT WAS OK FOR THE TERRAIN AND NOT TO CLB ABOVE 6000. AT THIS TIME; HE WAS ALREADY OUT OF 6600 AND I TOLD HIM TO STOP AT 7000 AND HE COMPLIED. SEPARATION WAS NOT LOST WITH LTT BUT IF ANY OTHER TFC HAD BEE NEARBY; WE MIGHT NOT HAVE BEEN SO LUCKY. THE PLT; WHEN QUESTIONED; STATED THAT HE HAD HEARD OF THIS HAPPENING BEFORE BUT NEVER TO HIM. HE SAID IF ANOTHER ACFT IS DIRECTLY ABOVE IT WILL SOMETIMES TRIGGER THE LOW ALT ALERT (GPWS). THE CLBING ACFT LTT WAS TCASII EQUIPPED; BUT APPARENTLY HAD NOTHING TO DO WITH THIS EVENT. ATX X WAS NOT TCASII EQUIPPED. TFC WAS NOT EXCHANGED DUE TO MORE THAN APPLICABLE SEPARATION BTWN THE TWO. ATC EQUIP (RADAR AND COM) WAS OPERATING NORMAL. SUPPLEMENTAL INFO FROM ACN 229841: ARR/DEP CTLR HAD INBOUND TFC; ATX X ON VECTORS FOR AN ILS APCH TO RWY 15 AT BTV. ATX X WAS LEVEL AT 5500 FT (THE MVA) OVER CAMEL'S HUMP (A 4088 FT MOUNTAIN 15 MI SE OF BTV). THE CTLR ALSO HAD A COMPANY LTT DEP CLBING THROUGH 8900 FT PASS DIRECTLY OVER THE ARR. AS THE 2 ACFT PASSED; ATX X GPWS INSTRUCTED THE PLT TO CLB IMMEDIATELY. THE PLT COMPLIED; THEN INFORMED THE CTLR THAT HE WAS IN A CLB BECAUSE OF THE WARNING. THE CTLR INSTRUCTED THE PLT NOT TO CLB ABOVE 6000 FT (7000 FT WAS THE ALT THE LTT WAS CLBING THROUGH WHEN THE ARTS TAGS MERGED). THE CTLR MOVED THE TAGS AND SAW THAT ATX X HAD CLBED TO 6600 FT; WHICH TURNED OUT NOT TO BE A PROB SINCE THE LTT WAS CLBING THROUGH 8900 FT. ATX X RETURNED TO 5500 FT ALMOST IMMEDIATELY BECAUSE HIS WARNING HAD CEASED. THE CTLR TOLD THE PLT ABOUT THE TFC THAT WAS DIRECTLY ABOVE HIM WHEN HE GOT THE ALARM. THE PLT SAID THAT HE THINKS THE RADAR ALTIMETER ON THE ACFT ABOVE HIM IS WHAT SET OFF HIS GPWS WARNING.