B747 FLT CREW HAS ALTDEV DURING DSCNT INTO JFK.

Narrative

THIS INCIDENT INVOLVES 3 PLTS: THE FLYING CAPT (ME); MY COPLT; AND A RELIEF CAPT. WE WERE NEARING THE END OF A 12 HR 17 MIN FLT TO JFK WHEN WE HAD AN ALTDEV. AFTER BEING CLRED DIRECT IGN AND WHILE AT CRUISE ALT; I LEFT THE COCKPIT FOR THE LAV AND TO TALK TO THE LEAD FLT ATTENDANT. THE RELIEF CAPT WAS IN THE COCKPIT AT THAT TIME AND SAT IN THE CAPT'S SEAT WHILE I WAS GONE. THAT WAY; NO ONE HAD TO WEAR AN OXYGEN MASK. WHEN I RETURNED HE WAS TRYING TO BUILD; WITH SOME DIFFICULTY; A WAYPOINT 35 MI THIS SIDE OF IGN. I SAT IN THE OBSERVER'S SEAT WHILE HE WAS DOING THIS AND WATCHED. AFTER HE GOT THE POINT BUILT; I TOLD HIM TO ENTER OUR CLRNC ALT. WHEN HE DID; THE COMPUTED DSCNT PATH SHOWED US TO BE VERY HIGH. HE NEXT TOLD CTR THAT THE ONLY WAY WE WOULD MAKE THAT XING RESTR WAS IF WE DID A 360 DEG TURN. CTR RESPONDED WITH 'DO THE BEST YOU CAN.' I THEN REOCCUPIED THE L SEAT AS THE PF AND SPD INTERVENED TO INCREASE THE RATE OF DSCNT. AS I STARTED TO LOOK OVER THE SIT; I BEGAN TO FEEL UNEASY ABOUT WHAT WAS HAPPENING AND THE CLRNC THAT I WAS TOLD THAT WE HAD RECEIVED. I THOUGHT; IF POSSIBLE; THAT THE RELIEF CAPT OR MY COPLT HAD MISUNDERSTOOD THE POINT WHERE WE WERE TO CROSS AT FL190. I ASKED CTR IF THEY MEANT FOR US TO CROSS 35 MI THIS SIDE OF IGN OR THE OTHER SIDE. CTR THEN ASKED WHAT OUR CURRENT ALT WAS AND THEN ALMOST SIMULTANEOUSLY TOLD US TO IMMEDIATELY STOP OUR DSCNT. I WAS THEN TOLD THAT WE HAD BEEN CLRED TO FL290; NOT FL190. WE WERE THEN GIVEN A CLRNC TO FL270 AND WERE TOLD THAT THERE HAD BEEN NO LOSS OF SEPARATION. I WAS OUT OF THE COCKPIT WHEN THE ORIGINAL CLRNC WAS RECEIVED. MY COPLT SAID THAT HE WROTE DOWN FL190 AND READ BACK FL190 AS THE CLRNC ALT. I DON'T KNOW IF THE RELIEF CAPT HEARD THE ORIGINAL CLRNC. IT IS POSSIBLE THAT HE DIDN'T PUT ON THE HEAD PHONES WHEN HE OCCUPIED THE L SEAT AS HE WAS ONLY GOING TO SIT THERE TEMPORARILY WHILE I WENT TO THE LAV. HE AND I HAVE BOTH FLOWN OVER 30 YRS IN THE AIRLINE SVC PLUS A FEW YRS IN THE NAVY. SOME OBSERVATIONS: 1) WHEN A PLT TELLS A CTLR THAT THE ONLY WAY HE OR SHE CAN MAKE A XING RESTR IS TO DO A 360 DEG TURN; THEN SOMETHING IS WRONG SOMEWHERE AND SHOULD BE LOOKED INTO. 2) IN A MULTI-CREWED SIT; IF YOU ARE GOING TO TEMPORARILY RELIEVE ANOTHER CREW MEMBER YOU SHOULD BE FULLY PREPARED TO ASSUME THE DUTIES OF THE SEAT YOU ARE OCCUPYING. 3) IF YOU HAVE THE CERTAIN 'FEELING' OR SOMETHING JUST DOESN'T SEEM QUITE RIGHT THEN START ASKING QUESTIONS.