Narrative:

During our climb to FL310 (the last climb clearance we received), ATC called out traffic at 12 O'clock at FL250. We were climbing through about FL238 at the time. Shortly thereafter, we saw the traffic and the TCASII alerted with traffic and we realized this could be a bad situation developing, so I began to level off as we were passing FL240. At the same time, I instructed the first officer to ask ATC if she wanted us to level off at FL240 (at this time we were level at FL243). She replied that that had been our clearance. I descended back to FL240 as the other aircraft passed overhead. We never heard, and therefore never responded to, any clearance to stop our climb at FL240. Center never called us to confirm and the first we knew of center's intentions was when we received the traffic call and asked the controller. This aircraft is equipped with an automatic leveloff feature which was in use and armed and we had been using the 'double paint' altitude confirmation method so I know the last clearance we heard prior to this was to climb to our filed altitude of FL310.

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Original NASA ASRS Text

Title: B727 CREW IN A CLB TO FL310 RECEIVED ADVISORY FROM ZME ARTCC CTLR ON TFC AT FL250. CREW LEVELED AT FL240 BUT WERE FAIRLY CERTAIN THEY HAD A CLRNC TO FL310.

Narrative: DURING OUR CLB TO FL310 (THE LAST CLB CLRNC WE RECEIVED), ATC CALLED OUT TFC AT 12 O'CLOCK AT FL250. WE WERE CLBING THROUGH ABOUT FL238 AT THE TIME. SHORTLY THEREAFTER, WE SAW THE TFC AND THE TCASII ALERTED WITH TFC AND WE REALIZED THIS COULD BE A BAD SIT DEVELOPING, SO I BEGAN TO LEVEL OFF AS WE WERE PASSING FL240. AT THE SAME TIME, I INSTRUCTED THE FO TO ASK ATC IF SHE WANTED US TO LEVEL OFF AT FL240 (AT THIS TIME WE WERE LEVEL AT FL243). SHE REPLIED THAT THAT HAD BEEN OUR CLRNC. I DSNDED BACK TO FL240 AS THE OTHER ACFT PASSED OVERHEAD. WE NEVER HEARD, AND THEREFORE NEVER RESPONDED TO, ANY CLRNC TO STOP OUR CLB AT FL240. CTR NEVER CALLED US TO CONFIRM AND THE FIRST WE KNEW OF CTR'S INTENTIONS WAS WHEN WE RECEIVED THE TFC CALL AND ASKED THE CTLR. THIS ACFT IS EQUIPPED WITH AN AUTOMATIC LEVELOFF FEATURE WHICH WAS IN USE AND ARMED AND WE HAD BEEN USING THE 'DOUBLE PAINT' ALT CONFIRMATION METHOD SO I KNOW THE LAST CLRNC WE HEARD PRIOR TO THIS WAS TO CLB TO OUR FILED ALT OF FL310.

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.