ACR X CLRNC TO WRONG ALT DSCNT THROUGH OCCUPIED ALT HAD TCASII RA CLB HAD LTSS FROM ACR Y. SYS ERROR. EVASIVE ACTION TAKEN.

Narrative

ACR X AT FL410 40 S SWL. I HAD TO HAVE ACR X AT FL370 PER 'MANOPS' BY 30 S SIE. I HAD 2 PIECES OF TFC AT FL390 15 N SBY AND ANOTHER 30 N SWL. I GAVE ACR X A CLRNC TO FL370 AND AFTER SEVERAL UPDATES; THE ACFT HAD NOT LEFT FL410. I TOLD ACR X TO BEGIN DSCNT AT 2000 FPM; WHICH THE PLT SAID WOULD BE NO PROBLEM. AFTER OBSERVING ACR X LEAVE FL373; I KNEW HE WAS NO LONGER A FACTOR FOR MY FL390 TFC. I BEGAN A RECORDED POS RELIEF BRIEFING AT THIS TIME AND MY ATTN WAS DIVERTED FROM ACR X. WHEN I NEXT NOTICED ACR X WAS OUT OF FL358 DSNDING HEAD-ON TO ACR Y AT FL350. AFTER LISTENING TO THE TAPES; I FOUND THAT INSTEAD OF ISSUING CLRNC TO FL370; I SAID FL270. MUCH TO MY DISMAY; I ALSO DID NOT CATCH THE PLTS READBACK. SUPPLEMENTAL INFO FROM ACN 211850: ACR X DSCNT WAS INITIATED USING VNAV AND THE AUTOPLT. EVEN BEFORE THE AUTOPLT HAD ATTAINED ITS NORMAL 1500 FPM DSCNT RATE TO A NEW CRUISE LEVEL; ZDC CALLED AND TOLD US TO INCREASE OUR RATE OF DSCNT TO OVER 2000 FPM. THE CAPT SWITCHED THE AUTOPLT TO VERT SPD MODE AND DIALED IN 2500 FPM. AT APPROX FL360; THE TCASII GAVE US A RA REQUIRING OVER 1700 FPM CLB. THE CAPT DISENGAGED THE AUTOPLT AND MANUALLY FLEW THE ACFT TO THE APPROPRIATE VERT CLB INDICATED BY THE TCASII TO AVOID TFC. IN THE TRANSITION FROM 2500 FPM DSCNT TO A 1700 FPM CLB; THE ACFT PROBABLY DSNDED TO FL355. EVEN BEFORE I COULD CALL CTR TO ASK ABOUT THE TFC; THEY CALLED US AND SAID WE WERE ONLY CLRED TO FL370 AND TO MAKE AN IMMEDIATE DSCNT TO FL330. I ADVISED THEM THAT WE HAD THE TCASII GENERATED RA AND WERE ALREADY IN A CLB TO AVOID TFC. I ALSO ADVISED THEM THAT I HAD READ BACK CLRNC TO FL270 AND THAT WE WOULD CONTINUE OUR CLB TO FL370 SINCE WE WERE ALREADY ABOVE FL360 AND STILL CLBING. JUST AS I COMPLETED MY XMISSION; I SAW TFC PASS DIRECTLY BELOW US AT WHAT THE TCASII INDICATED AS FL350.