Narrative:

We were approximately 2 mi northeast of benam intersection at FL270 getting ready to enter the published hold there when we were given a TA by the TCASII. I looked at my map display and saw the target climbing through 26900 ft. We then received an RA to descend. I started a descent. We also noticed the target was at our 12:30 O'clock position, so I initiated a left turn to further avoid the target. As soon as we started our evasive maneuver, the captain called ATC and told them what we were doing. ATC apparently did not realize what was happening prior to our call, but then immediately issued instructions for us to 'turn hard left.' we were already well into a left turn at this point and still descending. The TCASII RA strengthened to an 'increase descent,' which we followed. We then got a 'clear of conflict' that coincided with ATC instructions to climb back up to FL270 (we were around FL260). It is interesting to note that the target we were trying to avoid also appeared to start a descent as we were descending in response to our RA (they were on another frequency so we don't know if they did that because of TCASII or ATC instructions). I think that the hard turn away from the target was a crucial move in this case since we were both descending, and we didn't get the 'clear of conflict' until he was behind us. We were IMC the whole time! I believe the cause of this incident can be attributed to the continued practice of using similar flight numbers for aircraft being worked in the same airspace. The controller was extremely busy that morning. The denver airshow at the new airport was going on, and it completely shut down the eastern corridor, causing all traffic to be worked in from the west. Airplane were declaring low fuel and diverting everywhere. Our flight number was abc (X) and the other aircraft was bac (Y). They had been mixing us up all morning coming across the country. We couldn't hear the mixup that led to the conflict because they had changed frequencys. The area manager of den ATC later told us that (after listening to the tapes) the controller called bac and told him to maintain FL270 thinking he was calling abc. Bac started a climb to FL270. Thank goodness for TCASII and the left turn or the folks at the airshow would have really seen 'a show.' I think some guidelines need to be established that would prevent flts with similar flight numbers from being scheduled to work in the same airspace at the same time. This is a real safety issue that the FAA and commercial carriers need to deal with, especially in light of the growing demands put upon our ATC system.

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Original NASA ASRS Text

Title: 2 ACR ACFT HAD LTSS, OR POSSIBLY AN NMAC, IN IMC IN A HOLDING PATTERN.

Narrative: WE WERE APPROX 2 MI NE OF BENAM INTXN AT FL270 GETTING READY TO ENTER THE PUBLISHED HOLD THERE WHEN WE WERE GIVEN A TA BY THE TCASII. I LOOKED AT MY MAP DISPLAY AND SAW THE TARGET CLBING THROUGH 26900 FT. WE THEN RECEIVED AN RA TO DSND. I STARTED A DSCNT. WE ALSO NOTICED THE TARGET WAS AT OUR 12:30 O'CLOCK POS, SO I INITIATED A L TURN TO FURTHER AVOID THE TARGET. AS SOON AS WE STARTED OUR EVASIVE MANEUVER, THE CAPT CALLED ATC AND TOLD THEM WHAT WE WERE DOING. ATC APPARENTLY DID NOT REALIZE WHAT WAS HAPPENING PRIOR TO OUR CALL, BUT THEN IMMEDIATELY ISSUED INSTRUCTIONS FOR US TO 'TURN HARD L.' WE WERE ALREADY WELL INTO A L TURN AT THIS POINT AND STILL DSNDING. THE TCASII RA STRENGTHENED TO AN 'INCREASE DSCNT,' WHICH WE FOLLOWED. WE THEN GOT A 'CLR OF CONFLICT' THAT COINCIDED WITH ATC INSTRUCTIONS TO CLB BACK UP TO FL270 (WE WERE AROUND FL260). IT IS INTERESTING TO NOTE THAT THE TARGET WE WERE TRYING TO AVOID ALSO APPEARED TO START A DSCNT AS WE WERE DSNDING IN RESPONSE TO OUR RA (THEY WERE ON ANOTHER FREQ SO WE DON'T KNOW IF THEY DID THAT BECAUSE OF TCASII OR ATC INSTRUCTIONS). I THINK THAT THE HARD TURN AWAY FROM THE TARGET WAS A CRUCIAL MOVE IN THIS CASE SINCE WE WERE BOTH DSNDING, AND WE DIDN'T GET THE 'CLR OF CONFLICT' UNTIL HE WAS BEHIND US. WE WERE IMC THE WHOLE TIME! I BELIEVE THE CAUSE OF THIS INCIDENT CAN BE ATTRIBUTED TO THE CONTINUED PRACTICE OF USING SIMILAR FLT NUMBERS FOR ACFT BEING WORKED IN THE SAME AIRSPACE. THE CTLR WAS EXTREMELY BUSY THAT MORNING. THE DENVER AIRSHOW AT THE NEW ARPT WAS GOING ON, AND IT COMPLETELY SHUT DOWN THE EASTERN CORRIDOR, CAUSING ALL TFC TO BE WORKED IN FROM THE W. AIRPLANE WERE DECLARING LOW FUEL AND DIVERTING EVERYWHERE. OUR FLT NUMBER WAS ABC (X) AND THE OTHER ACFT WAS BAC (Y). THEY HAD BEEN MIXING US UP ALL MORNING COMING ACROSS THE COUNTRY. WE COULDN'T HEAR THE MIXUP THAT LED TO THE CONFLICT BECAUSE THEY HAD CHANGED FREQS. THE AREA MGR OF DEN ATC LATER TOLD US THAT (AFTER LISTENING TO THE TAPES) THE CTLR CALLED BAC AND TOLD HIM TO MAINTAIN FL270 THINKING HE WAS CALLING ABC. BAC STARTED A CLB TO FL270. THANK GOODNESS FOR TCASII AND THE L TURN OR THE FOLKS AT THE AIRSHOW WOULD HAVE REALLY SEEN 'A SHOW.' I THINK SOME GUIDELINES NEED TO BE ESTABLISHED THAT WOULD PREVENT FLTS WITH SIMILAR FLT NUMBERS FROM BEING SCHEDULED TO WORK IN THE SAME AIRSPACE AT THE SAME TIME. THIS IS A REAL SAFETY ISSUE THAT THE FAA AND COMMERCIAL CARRIERS NEED TO DEAL WITH, ESPECIALLY IN LIGHT OF THE GROWING DEMANDS PUT UPON OUR ATC SYS.

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.