Narrative:

We were flying from cancun, mexico to tampa, fl, on UB646 with the aircraft level at FL250. We were under the control of havana center, but not in radar contact yet. At approximately robin intersection, havana gave us a clearance to climb. The altitude I thought I heard was FL370. The copilot read back to havana FL370 and set 37000 in the altitude warning indicator. The captain acknowledged FL370 in accordance with our company procedures and started to climb the aircraft. Havana center did not question the coplts readback and no one in our cockpit raised the issue of possibly 'hearing an altitude other than FL370. When our aircraft was climbing through about 30500 ft MSL the copilot mentioned that his traffic alert and collision avoidance system (TCAS) indicator showed traffic above us and just of our right wing. We looked in this direction and saw another air carrier large transport. The captain stopped the climb at FL310. The copilot called aircraft Y to verify their altitude. They said they were level at FL330. At this point the copilot called havana center to ask about our altitude clearance. Havana responded that we were cleared to FL270. We told havana we were level at FL310. At this point havana said it was 'ok' to stay at FL310. A short time later, havana established radar contact and gave us separation vectors before handing us off to miami center. A contributing factor in this incident was that our flight plan showed FL370 as our final altitude. So, when havana issued our clearance to climb, we were expecting FL370. Another factor may have been the language barrier/difference involved. While the havana controllers english was very good, we did not hear FL270. Also, even though our copilot made a clear, distinct readback of the clearance, the controller did not hear FL370.

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Original NASA ASRS Text

Title: ALT DEV ALT OVERSHOT ALT EXCURSION.

Narrative: WE WERE FLYING FROM CANCUN, MEXICO TO TAMPA, FL, ON UB646 WITH THE ACFT LEVEL AT FL250. WE WERE UNDER THE CTL OF HAVANA CENTER, BUT NOT IN RADAR CONTACT YET. AT APPROX ROBIN INTXN, HAVANA GAVE US A CLRNC TO CLB. THE ALT I THOUGHT I HEARD WAS FL370. THE COPLT READ BACK TO HAVANA FL370 AND SET 37000 IN THE ALT WARNING INDICATOR. THE CAPT ACKNOWLEDGED FL370 IAW OUR COMPANY PROCS AND STARTED TO CLB THE ACFT. HAVANA CENTER DID NOT QUESTION THE COPLTS READBACK AND NO ONE IN OUR COCKPIT RAISED THE ISSUE OF POSSIBLY 'HEARING AN ALT OTHER THAN FL370. WHEN OUR ACFT WAS CLBING THROUGH ABOUT 30500 FT MSL THE COPLT MENTIONED THAT HIS TFC ALERT AND COLLISION AVOIDANCE SYS (TCAS) INDICATOR SHOWED TFC ABOVE US AND JUST OF OUR R WING. WE LOOKED IN THIS DIRECTION AND SAW ANOTHER ACR LGT. THE CAPT STOPPED THE CLB AT FL310. THE COPLT CALLED ACFT Y TO VERIFY THEIR ALT. THEY SAID THEY WERE LEVEL AT FL330. AT THIS POINT THE COPLT CALLED HAVANA CENTER TO ASK ABOUT OUR ALT CLRNC. HAVANA RESPONDED THAT WE WERE CLRED TO FL270. WE TOLD HAVANA WE WERE LEVEL AT FL310. AT THIS POINT HAVANA SAID IT WAS 'OK' TO STAY AT FL310. A SHORT TIME LATER, HAVANA ESTABLISHED RADAR CONTACT AND GAVE US SEPARATION VECTORS BEFORE HANDING US OFF TO MIAMI CENTER. A CONTRIBUTING FACTOR IN THIS INCIDENT WAS THAT OUR FLT PLAN SHOWED FL370 AS OUR FINAL ALT. SO, WHEN HAVANA ISSUED OUR CLRNC TO CLB, WE WERE EXPECTING FL370. ANOTHER FACTOR MAY HAVE BEEN THE LANGUAGE BARRIER/DIFFERENCE INVOLVED. WHILE THE HAVANA CTLRS ENGLISH WAS VERY GOOD, WE DID NOT HEAR FL270. ALSO, EVEN THOUGH OUR COPLT MADE A CLR, DISTINCT READBACK OF THE CLRNC, THE CTLR DID NOT HEAR FL370.

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.