ACR X DSCNT TO OCCUPIED ALT HAD LTSS FROM ACR Y. SYS ERROR.

Narrative

ACR X SHORTLY AFTER PASSING CALMA WE REQUESTED DSCNT TO FL350 AND RECEIVED IT. VERY SHORTLY AFTER REACHING FL350 ACR Y ASKED US IF WE COULD SEE THE ACFT BEHIND HIM AT FL350. WE HAD TALKED EARLIER WHEN HE PASSED BELOW US AND HE ASSUMED WE WERE AT FL370 YET. THE TARGET ON HIS TCASII WAS INTERMITTENT. HE SAID THE TARGET WAS 30 MI BEHIND HIM. WE WERE THE TARGET. SHORTLY AFTER THAT ATC CLRED US TO FL330 DUE TO TFC. WHEN QUERIED ABOUT TFC WE WERE TOLD IT WAS ACR Y. THE ONLY REASON WE CAUGHT THE LOSS OF SEPARATION WAS Y'S TCASII. SOME OF THESE TYPE SITS COULD BE AVOIDED BY HAVING TCASII WITH A RANGE GREATER THAN WE CURRENTLY HAVE. SUPPLEMENTAL INFO FROM ACN 310288: AFTER PASSING 'CALMA' WE REQUESTED DSCNT TO FL350 AND RECEIVED CLRNC. AFTER REACHING FL350 Y ASKED US ON PACIFIC REMOTE (128.95) IF WE COULD SEE THE ACFT AT FL350 BEHIND HIM AT 30 NM; DISPLAYED ON HIS TCASII. THAT ACFT WAS US. SHORTLY AFTER THAT TOKYO RADIO CLRED US TO FL330 'DUE TO TFC.' WE QUERIED TOKYO ABOUT THE TFC AND WERE TOLD IT WAS Y. TCASII WITH GREATER RANGE CAPABILITY CAUGHT THIS ERROR. NOPAC SEPARATION STANDARDS SAY 10 MINS OR LESS WITH MACH TECHNIQUE APPLIED.