AN ATCT LCL CTLR AND HIS DEVELOPMENTAL; MISJUDGED THE POS OF A TAXIING ACFT RELATIVE TO THE HOLD SHORT LINE. CONVINCED THE ACFT WAS BEHIND THE HOLD LINE; AN ARR WAS CLRED TO LAND WHILE THE ACFT HOLDING SHORT RPTED HAVING CROSSED THE HOLD SHORT LINE.

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I WAS TRAINING ON LCL CTL. MY DEVELOPMENTAL TAXIED INTO POS AND HOLD; ACR X ABC ON RWY 8. I IMMEDIATELY TOLD HIM THAT THAT WOULD NOT WORK BECAUSE WE HAD TFC ACR X DEF ON ABOUT 3 MI FINAL. SO HE INSTRUCTED ACR X ABC TO HOLD SHORT OF RWY 8. NO RESPONSE. SECOND TIME; NO RESPONSE. SINCE I DIDN'T GET A READBACK OF HIM HOLDING SHORT OF THE RWY; I TOOK THE POS AND INSTRUCTED ACR X ABC HOLD YOUR POS. AFTER THAT HE RESPONDED WITH ROGER. I OBSERVED THE ACFT STOP SHORT OF THE HOLD SHORT LINE AND I TOLD MY DEVELOPMENTAL TO ALSO LOOK AND SAID IF HE DID CROSS WE HAD TO SEND ACR X DEF AROUND. BUT TO BOTH OF US HE CLRLY WAS HOLDING SHORT. I KEPT CTLING THE TFC AROUND THE ARPT AND ABOUT 20 SECONDS LATER ACR X ABC WAS HEARD ON THE RECORDER SAYING HE WAS ACROSS THE HOLD SHORT LINE. BOTH MYSELF AND THE DEVELOPMENTAL MISSED THE CALL. BUT AS I SAID WE OBSERVED HIM SHORT OF THE LINE. WHEN ACR X DEF LANDED ON RWY 8 I INSTRUCTED ACR X ABC TO TAXI INTO POS AND HOLD AND HE SAID THAT IF WE HEARD HIM SAYING HE WAS ACROSS THE HOLD SHORT LINE. I TOLD HIM THAT I DIDN'T GET ANY XMISSION ON THAT EVENT. HE SAID THAT HE SAID IT 3 TIMES AND ON THE RECORDER ONLY SHOWED ONCE. THE FAA RULED THAT THERE WAS A CTLR OPERATIONAL ERROR. I DISAGREE DUE TO THE FACT THAT IF HE REALLY WAS ACROSS THE HOLD SHORT LINE I HAD ENOUGH TIME TO SEND THE OTHER ACFT AROUND BUT I OBSERVED THE ACFT. AND IF HE REALLY SAID IT 3 TIMES; THERE MUST HAVE BEEN SOME TYPE OF EQUIP MALFUNCTION. I DID WHAT HAD TO BE DONE AND NOW I'M BEING ACCUSED WHEN THERE IS NOTHING TO SAY OTHERWISE. I BELIEVE MY WORD IS THE TRUTH; MAYBE THE PLT OBSERVED SOME OTHER LINE.