OPERROR LTSS BTWN MIL C12 CLBING TO FL220 AND ACR B757 CLBING TO FL210. RPTR IN TRAINING AND THE OJT INSTRUCTOR THOUGHT THE C12 WAS AT FL220 WHEN THE B757 WAS CLRED TO FL210. RPTR SAID THE MIL C12 MODE C ALT READOUT WAS XXX FOR ABOUT A MIN AND A HALF. NO APPARENT ALT VERIFICATION WITH THE C12 BEFORE CLBING THE B757.

Narrative

I WAS RADAR TRAINING ON DEP SECTOR; WITH 5 HRS ON POS AND TRAINER DIDN'T HAVE MUCH EXPERIENCE AS TRAINER. IT WAS A BUSY DEP PUSH. A MIL C12 CLBING TO FL220 AND BEHIND SAME DIRECTION A B757 CLBING TO FL210. THE C12 MODE C HAD BEEN XXX FOR AT LEAST A MIN AND A HALF. I THOUGHT THE C12 WAS LEVEL AT FL220 AND CLBED THE B757 TO FL210. WHEN THE C12 MODE C CAME BACK ON IT SHOWED FL210 CLBING TO FL220. THE B757 WAS ALREADY SHOWING FL200 CLBING TO FL210; WITHIN 5 MI OF THE C12. AT THAT TIME THE C12 WAS TOLD TO EXPEDITE TO FL220 AND THE B757 TO MAINTAIN FL200; BUT SEPARATION WAS ALREADY LOST. I THINK THE C12'S XPONDER WAS NOT WORKING PROPERLY. IT HAD NOT SHOWN AN ALT FOR A WHILE; AND I THINK IF IT WAS WORKING THE B757'S TCASII WOULD HAVE GIVEN A TA OR RA SO AS TO NOT CLB INTO THE C12. I HAD NOT LOST THE PICTURE COMPLETELY; BUT I WAS GETTING BEHIND; AS I ONLY HAD 5 HRS TOTAL ON POS. SUPPLEMENTAL INFO FROM ACN 374793: THIS INCIDENT OCCURRED BECAUSE THE MIL'S KING AIR MODE C DID NOT UPDATE PROPERLY AND THE OJT INSTRUCTOR'S LACK OF EXPERIENCE CONDUCTING TRAINING.