Narrative:

We received a TCASII warning over los mochis VOR in mexico. We then received a climb command for traffic and vacated FL310, our assigned altitude, for FL320. We cleared the traffic by 1300 ft on our TCASII. After clearing the traffic we notified mazatlan center and returned to our assigned altitude, FL310. A few mins later air carrier #2 flight, also assigned to FL310, received the same warning and climbed to avoid traffic. There were 3 aircraft in the vicinity of LMM VOR -- our flight, air carrier #2 flight, and an air carrier #3 flight. We were on J8 over LMM VOR at FL310 heading 200 degrees when our TCASII showed a conflicting aircraft at our 2 O'clock position and 300 ft below us. We were given a climb command by the TCASII which we complied with. The conflicting traffic passed directly under us at 1300 ft on the TCASII. We saw the traffic after he passed us and it appeared to be a white air carrier heading southeast. A few mins later air carrier #3 received the same warning. They were approximately 35 NM southeast of LMM at FL310. I believe that the conflicting traffic was air carrier #2 flight at the wrong altitude, either flying at FL310 or did not have 29.92 set on his altimeter because he was 300 ft off his altitude. Supplemental information from acn 236953: it was at this point that it dawned on us that the TCASII had been MEL'ed on an earlier flight and should have been in the transponder position only. It's possible that the RA to climb was erroneous.

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Original NASA ASRS Text

Title: 3 ACR ACFT WERE NEAR, OR OVER, A VOR AT HIGH ALT AT THE SAME TIME, 2 AT THE SAME ALT AND 1 2000 FT BELOW CAUSING 2 ACFT TO DEVIATE FROM ASSIGNED ALT IN RESPONSE TO A TCASII RA.

Narrative: WE RECEIVED A TCASII WARNING OVER LOS MOCHIS VOR IN MEXICO. WE THEN RECEIVED A CLB COMMAND FOR TFC AND VACATED FL310, OUR ASSIGNED ALT, FOR FL320. WE CLRED THE TFC BY 1300 FT ON OUR TCASII. AFTER CLRING THE TFC WE NOTIFIED MAZATLAN CTR AND RETURNED TO OUR ASSIGNED ALT, FL310. A FEW MINS LATER ACR #2 FLT, ALSO ASSIGNED TO FL310, RECEIVED THE SAME WARNING AND CLBED TO AVOID TFC. THERE WERE 3 ACFT IN THE VICINITY OF LMM VOR -- OUR FLT, ACR #2 FLT, AND AN ACR #3 FLT. WE WERE ON J8 OVER LMM VOR AT FL310 HDG 200 DEGS WHEN OUR TCASII SHOWED A CONFLICTING ACFT AT OUR 2 O'CLOCK POS AND 300 FT BELOW US. WE WERE GIVEN A CLB COMMAND BY THE TCASII WHICH WE COMPLIED WITH. THE CONFLICTING TFC PASSED DIRECTLY UNDER US AT 1300 FT ON THE TCASII. WE SAW THE TFC AFTER HE PASSED US AND IT APPEARED TO BE A WHITE ACR HDG SE. A FEW MINS LATER ACR #3 RECEIVED THE SAME WARNING. THEY WERE APPROX 35 NM SE OF LMM AT FL310. I BELIEVE THAT THE CONFLICTING TFC WAS ACR #2 FLT AT THE WRONG ALT, EITHER FLYING AT FL310 OR DID NOT HAVE 29.92 SET ON HIS ALTIMETER BECAUSE HE WAS 300 FT OFF HIS ALT. SUPPLEMENTAL INFO FROM ACN 236953: IT WAS AT THIS POINT THAT IT DAWNED ON US THAT THE TCASII HAD BEEN MEL'ED ON AN EARLIER FLT AND SHOULD HAVE BEEN IN THE XPONDER POS ONLY. IT'S POSSIBLE THAT THE RA TO CLB WAS ERRONEOUS.

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.