Narrative:

En route at FL330 eastbound on J42 100 northwest west of dfw. We requested FL370. Controller initially said unable but would keep us advised. He called back and cleared us to FL370, but as we passed FL340 he told us to stop at FL350. When we arrived at FL350, he told us to climb immediately to FL370 and be level in 1 min. I acknowledged and first officer started climb. We observed a head-on aircraft and controller came back and issued evasive turns to us both (to the right) and told us to stop climb (we were at FL360). Both aircraft had 4 digit call signs with only the second digit different. I was very concerned that either we or the other aircraft had accepted the wrong clearance. I was also concerned that I might have made a mistake leaving the evasive flying to the first officer. Subsequent review of the cockpit voice recorder proved however that both aircraft responded to their appropriate clrncs and ironically, had we been able to climb faster, we might have hit. The other aircraft passed at our newly assigned altitude of FL370, so our weight and turn limited rate of climb saved our lives.

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Original NASA ASRS Text

Title: AT PLT REQUEST, CTLR ISSUES CLB THROUGH OCCUPIED ALT RESULTING IN LTSS.

Narrative: ENRTE AT FL330 EBOUND ON J42 100 NW W OF DFW. WE REQUESTED FL370. CTLR INITIALLY SAID UNABLE BUT WOULD KEEP US ADVISED. HE CALLED BACK AND CLRED US TO FL370, BUT AS WE PASSED FL340 HE TOLD US TO STOP AT FL350. WHEN WE ARRIVED AT FL350, HE TOLD US TO CLB IMMEDIATELY TO FL370 AND BE LEVEL IN 1 MIN. I ACKNOWLEDGED AND FO STARTED CLB. WE OBSERVED A HEAD-ON ACFT AND CTLR CAME BACK AND ISSUED EVASIVE TURNS TO US BOTH (TO THE R) AND TOLD US TO STOP CLB (WE WERE AT FL360). BOTH ACFT HAD 4 DIGIT CALL SIGNS WITH ONLY THE SECOND DIGIT DIFFERENT. I WAS VERY CONCERNED THAT EITHER WE OR THE OTHER ACFT HAD ACCEPTED THE WRONG CLRNC. I WAS ALSO CONCERNED THAT I MIGHT HAVE MADE A MISTAKE LEAVING THE EVASIVE FLYING TO THE FO. SUBSEQUENT REVIEW OF THE COCKPIT VOICE RECORDER PROVED HOWEVER THAT BOTH ACFT RESPONDED TO THEIR APPROPRIATE CLRNCS AND IRONICALLY, HAD WE BEEN ABLE TO CLB FASTER, WE MIGHT HAVE HIT. THE OTHER ACFT PASSED AT OUR NEWLY ASSIGNED ALT OF FL370, SO OUR WT AND TURN LIMITED RATE OF CLB SAVED OUR LIVES.

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.