Narrative:

I received a radar handoff from ZLA on air carrier X descending to 14000 ft. I was providing ATC services to MTR eastbound at 10000 ft. The MTR was assigned a vector of 100 degrees and was level at 10000 ft. Air carrier X checked onto the frequency and was issued a descent to cross the pmd VORTAC at or below 13000 ft maintain 11000 ft. I observed a VFR target approximately 4-5 mi south of the pmd VORTAC at 11500 ft unverified. Air carrier X was on converging courses with the target at 11500 ft. I elected to have air carrier X expedite descent to and maintain 11000 ft for VFR traffic 12 O'clock, 10 mi. Air carrier X reached the assigned altitude approximately 6-8 mi from the VFR target. The MTR was still on an assigned heading of 100 degrees and was rapidly closing on air carrier X on converging courses. By this time, appropriate IFR/VFR separation did exist between the 3 affected aircraft. Neither of the affected aircraft were nearer than 5 mi from one another. Initially, air carrier X had responded to a TCASII RA from the VFR target. Air carrier X had initially deviated from the assigned altitude but separation was not lost as air carrier X opted to arrest the descent and return to the assigned altitude. At this point in time, air carrier X was approximately 10 mi, at its closest point, to the MTR. I concluded from past practice that this scenario had potential to be a TCASII nightmare and immediately commenced issuing air carrier X as traffic to the MTR. The MTR was unable to visually make contact with air carrier X. I then commenced to inform air carrier X of the MTR traffic, 1 O'clock, 10 mi, eastbound, IFR, 10000 ft. Air carrier X acknowledged the traffic but did not report it as being in sight. At approximately 2 mi from the VFR target and approximately 1 mi from MTR air carrier X advised they were responding to a TCASII RA and were descending and turning. I immediately advised MTR of air carrier X intentions of responding to the TCASII RA, and issued an immediate turn to the left heading 070. MTR advised that he had visual contact on air carrier X and I advised MTR to maintain visual separation from air carrier X as he was responding to a TCASII RA. Air carrier X advised he had obtained visual contact with the MTR as it passed below. Air carrier X advised that no visual contact had been made on the VFR target.

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Original NASA ASRS Text

Title: ACR X TCASII RA FROM VFR ACFT HAD LTSS FROM MTR. PLTDEV. TCASII INDUCED LTSS.

Narrative: I RECEIVED A RADAR HDOF FROM ZLA ON ACR X DSNDING TO 14000 FT. I WAS PROVIDING ATC SVCS TO MTR EBOUND AT 10000 FT. THE MTR WAS ASSIGNED A VECTOR OF 100 DEGS AND WAS LEVEL AT 10000 FT. ACR X CHKED ONTO THE FREQ AND WAS ISSUED A DSCNT TO CROSS THE PMD VORTAC AT OR BELOW 13000 FT MAINTAIN 11000 FT. I OBSERVED A VFR TARGET APPROX 4-5 MI S OF THE PMD VORTAC AT 11500 FT UNVERIFIED. ACR X WAS ON CONVERGING COURSES WITH THE TARGET AT 11500 FT. I ELECTED TO HAVE ACR X EXPEDITE DSCNT TO AND MAINTAIN 11000 FT FOR VFR TFC 12 O'CLOCK, 10 MI. ACR X REACHED THE ASSIGNED ALT APPROX 6-8 MI FROM THE VFR TARGET. THE MTR WAS STILL ON AN ASSIGNED HDG OF 100 DEGS AND WAS RAPIDLY CLOSING ON ACR X ON CONVERGING COURSES. BY THIS TIME, APPROPRIATE IFR/VFR SEPARATION DID EXIST BTWN THE 3 AFFECTED ACFT. NEITHER OF THE AFFECTED ACFT WERE NEARER THAN 5 MI FROM ONE ANOTHER. INITIALLY, ACR X HAD RESPONDED TO A TCASII RA FROM THE VFR TARGET. ACR X HAD INITIALLY DEVIATED FROM THE ASSIGNED ALT BUT SEPARATION WAS NOT LOST AS ACR X OPTED TO ARREST THE DSCNT AND RETURN TO THE ASSIGNED ALT. AT THIS POINT IN TIME, ACR X WAS APPROX 10 MI, AT ITS CLOSEST POINT, TO THE MTR. I CONCLUDED FROM PAST PRACTICE THAT THIS SCENARIO HAD POTENTIAL TO BE A TCASII NIGHTMARE AND IMMEDIATELY COMMENCED ISSUING ACR X AS TFC TO THE MTR. THE MTR WAS UNABLE TO VISUALLY MAKE CONTACT WITH ACR X. I THEN COMMENCED TO INFORM ACR X OF THE MTR TFC, 1 O'CLOCK, 10 MI, EBOUND, IFR, 10000 FT. ACR X ACKNOWLEDGED THE TFC BUT DID NOT RPT IT AS BEING IN SIGHT. AT APPROX 2 MI FROM THE VFR TARGET AND APPROX 1 MI FROM MTR ACR X ADVISED THEY WERE RESPONDING TO A TCASII RA AND WERE DSNDING AND TURNING. I IMMEDIATELY ADVISED MTR OF ACR X INTENTIONS OF RESPONDING TO THE TCASII RA, AND ISSUED AN IMMEDIATE TURN TO THE L HDG 070. MTR ADVISED THAT HE HAD VISUAL CONTACT ON ACR X AND I ADVISED MTR TO MAINTAIN VISUAL SEPARATION FROM ACR X AS HE WAS RESPONDING TO A TCASII RA. ACR X ADVISED HE HAD OBTAINED VISUAL CONTACT WITH THE MTR AS IT PASSED BELOW. ACR X ADVISED THAT NO VISUAL CONTACT HAD BEEN MADE ON THE VFR TARGET.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.