SYS ERROR DURING A POTENTIAL CONFLICT WITH A LATE TURN BY ATC AND A DSCNT THROUGH OCCUPIED ALT WITH TCASII ON YELLOW; NO TA-RA NEAR PMD; CA.

Narrative

WE WERE DSNDING; HAVING BEEN CLRED TO DSND TO CROSS PMD AT FL230 ON THE ZIGGY 3 ARR. THE ATC CTLR CALLED US AS WE WERE JUST ABOUT OVER PMD AND APCHING FL230 AND; WITH A VERY TENSE VOICE; TOLD US TO 'IMMEDIATELY TURN 40 DEGS L AND EXPEDITE TO FL210.' WE WERE WATCHING TFC COMING TOWARD US; BOTH VISUALLY AND ON TCASII. THE APCHING ACFT'S ALT WAS BEING RPTED AS 2000 FT BELOW US AS WE STARTED THE TURN OFF COURSE. AT SOME POINT IN THESE EXCHANGES THE CTLR CLRED US TO CROSS HITOP AT 13000 FT. THE TURN WAS ACCELERATED AS WAS THE RATE OF DSCNT. THE APCHING ACFT'S SYMBOL PASSED WELL TO THE W AND WE CONTINUED OUR DSCNT BELOW HIS ALT. WE MAINTAINED VISUAL CONTACT WITH THE ACFT UNTIL HE PASSED OUT OF OUR VIEW; BEHIND US. THE CTLR CONFIRMED WE WERE PASSING FL210. THE TFC WAS WELL TO OUR R AND BEHIND US BY THIS TIME. WE TOLD THE CTLR WE WERE TURNING TO COURSE; IF THAT WAS OK WITH HIM. HE CONFIRMED OUR CLRNC TO RETURN TO COURSE. FROM THE SOUND OF HIS VOICE; THIS OCCURRENCE WAS MORE EXCITING FOR THE CTLR THAN FOR US. WE CONTINUED OUR DSCNT; LNDG AT ONT WITHOUT INCIDENT. THERE WAS SOME CONVERSATION WITH THE CTLR; WITH HIM SAYING THE OTHER ACFT WAS OFF COURSE. HOWEVER; FROM MY PERSPECTIVE; NO HAZARDOUS CONDITION EXISTED AT ANY TIME. WE WERE WATCHING THE ACFT SYMBOL ON THE TCASII. IT HAD TURNED YELLOW AND WAS BELOW OUR ALT. THE INITIAL INSTRUCTION FROM THE CTLR WAS TO EXPEDITE THE DSCNT. IT WAS FOLLOWED BY TURN 40 DEGS L. I'M NOT TOO SURE I AGREED WITH THE CTLR AT THAT POINT. THE TARGET ACFT WAS OBLIVIOUSLY CLBING TO OUR POS AND WE WERE DSNDING TO HIS. IT WAS MY INCLINATION TO STOP THE DSCNT AND TURN. THAT IS WHAT THE TCASII WAS INDICATING. THE INSTRUCTION TO EXPEDITE THE DSCNT WAS CONTRARY TO WHAT THE TCASII WAS INDICATING. WHILE OUR FOM DOES NOT DIRECTLY ADDRESS THE ISSUE; '...MUST IMMEDIATELY RESPOND TO TCASII INFO BY USING THE TCASII GUIDELINES.' FURTHER; UNDER THE CAUTION; 'SAFE SEPARATION COULD BE COMPROMISED IF CURRENT VERT SPD IS CHANGED.' IN THIS CASE; STOPPING THE DSCNT WAS WHAT THE TCASII WAS INDICATING. THIS FOM GUIDANCE IS PRIMARILY DIRECTED AT RA'S. 3 THINGS BOTHER ME ABOUT THIS OCCURRENCE: 1) IF I HAD JUST BEEN LEFT ON MY OWN; I WOULD HAVE STOPPED THE DSCNT. 2) FOLLOWING THE DSCNT INSTRUCTIONS OF THE CTLR SEEMED TO AGGRAVATE THE SIT. 3) THE FOM DOES NOT ADDRESS THIS TYPE OF TA SIT. HOWEVER; LET ME SHARE WITH YOU SOME FEELINGS I HAVE CONCERNING THE CTLR; TCASII; PLT TRIANGLE. WHEN FLYING; WE DEVELOP A RELATIONSHIP WITH THE CTLR; HOWEVER BRIEF. I WAS COMPELLED TO FOLLOW HIS INSTRUCTIONS. I KNEW FROM THE TCASII THAT I SHOULD HAVE STOPPED THE DSCNT. I DIDN'T BECAUSE THE CTLR INSTRUCTED ME TO EXPEDITE THE DSCNT. LATER; IN MY HOTEL ROOM; I WAS THINKING OF THE CREW THAT HAD A COLLISION WITH THE FOREIGN CHARTER FLT. THAT CREW OPERATED UNDER THE SAME 'RELATIONSHIP' WITH THE CTLR; THE SAME MODE OF BEHAVIOR THAT I WAS UNDER. FORTUNATELY; A MUCH DIFFERENT OUTCOME.