Narrative:

Flight from san jose, costa rica, was 80 mi south of mydia intersection on high altitude route UB881, bound for atlanta, GA. The first officer was flying the aircraft on autoplt at FL390. The captain was calling ZHU 10 mins prior to entering us airspace. While the captain was on radio #2, merdia controller on frequency 128.2 cleared the flight to FL300. The first officer acknowledged the altitude change and started the aircraft down. When the captain completed his call, the first officer related this information to the captain. Passing FL334, merdia center asked our altitude and instructed us to return to FL370. They told us we were not cleared to FL300. We climbed to FL370 with no further conversation or difficulty. Foreign accents were certainly a contributing factor. Voiceless communication would have been a great help. Supplemental information from acn 582591: we were told to expect FL300 in a few mins. The first officer, who was flying, was the only one on frequency. The controller said descend and maintain FL300. I heard FL300, I read back FL300. We do not believe separation was lost. Language was definitely a contributing factor to this incident. Normally both pilots are listening to xmissions to avoid this type of confusion but the timing was right where the captain had to call ahead. I am certain I heard FL300 and I know I read back FL300.

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Original NASA ASRS Text

Title: ENRTE ALT CHANGE OVERSHOT WHEN FO, PF, HEARS CLRNC TO FL300 VERSUS ATC ALLEGEDLY ASSIGNED FL370 80 MI S OF MYDIA INTXN, FO.

Narrative: FLT FROM SAN JOSE, COSTA RICA, WAS 80 MI S OF MYDIA INTXN ON HIGH ALT RTE UB881, BOUND FOR ATLANTA, GA. THE FO WAS FLYING THE ACFT ON AUTOPLT AT FL390. THE CAPT WAS CALLING ZHU 10 MINS PRIOR TO ENTERING US AIRSPACE. WHILE THE CAPT WAS ON RADIO #2, MERDIA CTLR ON FREQ 128.2 CLRED THE FLT TO FL300. THE FO ACKNOWLEDGED THE ALT CHANGE AND STARTED THE ACFT DOWN. WHEN THE CAPT COMPLETED HIS CALL, THE FO RELATED THIS INFO TO THE CAPT. PASSING FL334, MERDIA CTR ASKED OUR ALT AND INSTRUCTED US TO RETURN TO FL370. THEY TOLD US WE WERE NOT CLRED TO FL300. WE CLBED TO FL370 WITH NO FURTHER CONVERSATION OR DIFFICULTY. FOREIGN ACCENTS WERE CERTAINLY A CONTRIBUTING FACTOR. VOICELESS COM WOULD HAVE BEEN A GREAT HELP. SUPPLEMENTAL INFO FROM ACN 582591: WE WERE TOLD TO EXPECT FL300 IN A FEW MINS. THE FO, WHO WAS FLYING, WAS THE ONLY ONE ON FREQ. THE CTLR SAID DSND AND MAINTAIN FL300. I HEARD FL300, I READ BACK FL300. WE DO NOT BELIEVE SEPARATION WAS LOST. LANGUAGE WAS DEFINITELY A CONTRIBUTING FACTOR TO THIS INCIDENT. NORMALLY BOTH PLTS ARE LISTENING TO XMISSIONS TO AVOID THIS TYPE OF CONFUSION BUT THE TIMING WAS RIGHT WHERE THE CAPT HAD TO CALL AHEAD. I AM CERTAIN I HEARD FL300 AND I KNOW I READ BACK FL300.

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.