Narrative:

We were in cruise at FL220 in TCAS equipped medium large transport. Approximately 50 NM west of the ape VOR on the blunt arrival at approximately xx:35 local time, we received a TA from the TCAS showing the other aircraft 2400' below us and climbing at our 12 O'clock position at a range of approximately 5 NM. Shortly thereafter, we received an RA instructing us to climb and the RA/vsi lights indicated an 1100-1300 FPM climb to be needed. I disconnected the autoplt and immediately climbed while instructing the first officer to contact ATC and inform them of our deviation and the reason for it. We reached approximately FL228 when the 'clear of conflict' message was received. ATC questioned the other aircraft who had been cleared to FL210 if he had deviated from that altitude, to which he replied, 'negative.' it would appear that the TCAS seeing the intruding aircraft climbing toward us at perhaps a high rate of climb considered it a threat to our aircraft. The TCAS obviously did not know that the other aircraft was going to level off 1000' below us and therefore issued the RA. At the time of the incident, the other aircraft was in the clouds and we were in and out of the tops making visibility contact impossible (we never did see the other aircraft). ATC had not issued the traffic to us previously, but only informed us of his position after we began to climb and called about the deviation. Due to the restriction to visibility below us, even if the traffic had been called earlier by ATC as, for example, '12 O'clock and 7 mi, climbing to FL210,' I would have followed the RA in any case as per our training, thinking perhaps the other aircraft had busted his altitude or was deviating for some other reason. Had the WX been better, we may have gotten a visibility on the other aircraft when the TA was issued and avoided the subsequent deviation. I don't know the technicalities involved or if it can be done but the only solution I see is to somehow change the TCAS logic so that RA's are not issued for climbing or descending conflicts until they are less than 1000' from the other aircraft. This would obviously lessen the available reaction time which is probably unacceptable. In spite of this incident I am a firm believer in this system, but as with any other new technology, it will take a little time to get all of the bugs worked out.

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Original NASA ASRS Text

Title: ACR HAS TCASII RA. RESPONDS WITH CLIMB.

Narrative: WE WERE IN CRUISE AT FL220 IN TCAS EQUIPPED MLG. APPROX 50 NM W OF THE APE VOR ON THE BLUNT ARR AT APPROX XX:35 LCL TIME, WE RECEIVED A TA FROM THE TCAS SHOWING THE OTHER ACFT 2400' BELOW US AND CLBING AT OUR 12 O'CLOCK POS AT A RANGE OF APPROX 5 NM. SHORTLY THEREAFTER, WE RECEIVED AN RA INSTRUCTING US TO CLB AND THE RA/VSI LIGHTS INDICATED AN 1100-1300 FPM CLB TO BE NEEDED. I DISCONNECTED THE AUTOPLT AND IMMEDIATELY CLBED WHILE INSTRUCTING THE F/O TO CONTACT ATC AND INFORM THEM OF OUR DEVIATION AND THE REASON FOR IT. WE REACHED APPROX FL228 WHEN THE 'CLR OF CONFLICT' MESSAGE WAS RECEIVED. ATC QUESTIONED THE OTHER ACFT WHO HAD BEEN CLRED TO FL210 IF HE HAD DEVIATED FROM THAT ALT, TO WHICH HE REPLIED, 'NEGATIVE.' IT WOULD APPEAR THAT THE TCAS SEEING THE INTRUDING ACFT CLBING TOWARD US AT PERHAPS A HIGH RATE OF CLB CONSIDERED IT A THREAT TO OUR ACFT. THE TCAS OBVIOUSLY DID NOT KNOW THAT THE OTHER ACFT WAS GOING TO LEVEL OFF 1000' BELOW US AND THEREFORE ISSUED THE RA. AT THE TIME OF THE INCIDENT, THE OTHER ACFT WAS IN THE CLOUDS AND WE WERE IN AND OUT OF THE TOPS MAKING VIS CONTACT IMPOSSIBLE (WE NEVER DID SEE THE OTHER ACFT). ATC HAD NOT ISSUED THE TFC TO US PREVIOUSLY, BUT ONLY INFORMED US OF HIS POS AFTER WE BEGAN TO CLB AND CALLED ABOUT THE DEVIATION. DUE TO THE RESTRICTION TO VISIBILITY BELOW US, EVEN IF THE TFC HAD BEEN CALLED EARLIER BY ATC AS, FOR EXAMPLE, '12 O'CLOCK AND 7 MI, CLBING TO FL210,' I WOULD HAVE FOLLOWED THE RA IN ANY CASE AS PER OUR TRNING, THINKING PERHAPS THE OTHER ACFT HAD BUSTED HIS ALT OR WAS DEVIATING FOR SOME OTHER REASON. HAD THE WX BEEN BETTER, WE MAY HAVE GOTTEN A VIS ON THE OTHER ACFT WHEN THE TA WAS ISSUED AND AVOIDED THE SUBSEQUENT DEVIATION. I DON'T KNOW THE TECHNICALITIES INVOLVED OR IF IT CAN BE DONE BUT THE ONLY SOLUTION I SEE IS TO SOMEHOW CHANGE THE TCAS LOGIC SO THAT RA'S ARE NOT ISSUED FOR CLBING OR DSNDING CONFLICTS UNTIL THEY ARE LESS THAN 1000' FROM THE OTHER ACFT. THIS WOULD OBVIOUSLY LESSEN THE AVAILABLE REACTION TIME WHICH IS PROBABLY UNACCEPTABLE. IN SPITE OF THIS INCIDENT I AM A FIRM BELIEVER IN THIS SYS, BUT AS WITH ANY OTHER NEW TECHNOLOGY, IT WILL TAKE A LITTLE TIME TO GET ALL OF THE BUGS WORKED OUT.

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.