B747 LANDS ON CLOSED PORTION OF RWY AT JFK.

Narrative

RWY 31L&R WERE IN USE. THE RWY 31L DISPLACED THRESHOLD WAS CLOSED; AS IT HAS BEEN FOR MONTHS; DUE TO A PAVEMENT FAILURE DURING THE WINTER MONTHS. MEN AND EQUIP WERE WORKING ON IT EARLIER IN THE DAY; MAKING REPAIRS. RWY 31L DEPS ARE UTILIZING INTXN K AND KA NEAR THE DISPLACED THRESHOLD FOR DEP. BECAUSE THIS RWY CLOSURE WAS ON THE DISPLACED THRESHOLD; THE LNDG LENGTH OF THE RWY WAS UNCHANGED. A B747 WAS ASSIGNED A VISUAL APCH TO RWY 31L. HE CALLED INBOUND. I ISSUED THE WIND (APPROX 200 DEGS AT 4 KTS); A SLIGHT TAILWIND; AND I CLRED THE ACFT TO LAND ON RWY 31L. AS I WAS ACCOMMODATING A VFR HELI DEP; I HEARD THE AMASS ALERT SOUND. I QUICKLY ASSESSED THE SIT; SCANNING THE RWY AND LOCATING THE HELI. I OBSERVED THE B747 LAND ON THE DISPLACED THRESHOLD. I FEEL THAT THE ALARM SOUNDED TOO LATE AND THERE WAS NOT ENOUGH TIME FOR THE ACFT TO EXECUTE A MISSED APCH. WHEN THE ALARM SOUNDED; THE ACFT WAS WELL OVER THE RWY PAVEMENT; 'A LANDER;' AND FLARED FOR TOUCHDOWN. THUS; I DID NOT ORDER THE ACFT TO GO AROUND. THE ACFT LANDED BEYOND THE ARPT MGR WHO WAS IN A VEHICLE OPERATING ON THE CLOSED PORTION; IN THE PROCESS OF REOPENING A PORTION OF THE RWY. AFTER THE INCIDENT; I WAS ADVISED THAT THE AMASS RWY CONFIGN WAS INCORRECTLY SET. HAVING NEVER HEARD OF THIS BEFORE; I WAS ADVISED THAT EQUIP WADS SET ON '3131;' WHICH IS FOR OPS UTILIZING THE FULL LENGTH. APPARENTLY; THERE WAS A SETTING CALLED 'DP31' THAT SHOULD HAVE BEEN USED. I SPOKE TO A FEW CTLRS AND MOST HAD HAD NO IDEA WHAT 'DP31' MEANS. THIS SETTING SHOULD HAVE BEEN MONITORED BY THE SUPVR. ADDITIONALLY; WE ASKED THE AIRWAYS FACILITIES RADAR TECHNICIAN ABOUT THE AMASS SETTINGS AND HE WAS NOT SURE OF WHAT THE DIFFERENCES WERE. I DO NOT KNOW IF THE ALARM WOULD HAVE SOUNDED EARLIER AND A GAR COULD HAVE BEEN ISSUED AND OBEYED OR IF THE ALARM WOULD HAVE BEEN SUPPRESSED AND NO WARNING HEARD ON THIS ALTERNATIVE AMASS SETTING. THE AIRWAYS FACILITIES RADAR TECHNICIAN WAS UNSURE. ADDITIONALLY; I WAS ADVISED THAT THE NEW YORK APCH CTLR DID NOT VERIFY THAT THE PLT HAD THE CURRENT ATIS; WHICH CONTAINED THE RWY CLOSURE INFO. SINCE I STARTED WORKING AT JFK ARPT; THE ARPT OPERATOR (THE PORT AUTH OF NEW YORK AND NEW JERSEY); HAS ROUTINELY CLOSED PORTIONS OF THE ACTIVE RWY AND THE TWR HAS CONTINUED TO OPERATE ACFT OVER THE CLOSED PORTIONS. ADDITIONALLY; WITH THIS PARTIAL RWY CLOSURE; VISUAL APCHS (NON PRECISION APCHS) HAVE BEEN AUTH ROUTINELY. THIS OP IS EXTREMELY DANGEROUS! I DO NOT FEEL THAT ANY PART OF AN ACTIVE RWY SHOULD BE CLOSED WITH MEN AND EQUIP WORKING ON THEM. CLOSE THE ENTIRE RWY! AND IF THAT IS NOT POSSIBLE; I BELIEVE THAT THERE SHOULD BE A RULING WHICH MANDATES A PRECISION APCH FOR THESE CIRCUMSTANCES; IN THE VERY LEAST. IT IS MY UNDERSTANDING THAT THE REASON FOR A DISPLACED THRESHOLD IS TO ENSURE OBSTACLE CLRNC. THEN WHY WOULD IT BE APPROPRIATE TO PUT MEN AND EQUIP ON AN ACTIVE RWY DISPLACED THRESHOLD AND NOT PROTECT FOR THEM? THEY ARE NOW A NEW OBSTRUCTION TO LNDG ACFT. I FIND THESE PRACTICES DISTURBING AND HAVE SEEN FIRSTHAND WHAT CAN HAPPEN IF THE PLT DOES NOT LAND THEIR ACFT PERFECTLY.