Narrative:

I was working a midnight shift, and although I have been an fpl for over 5 yrs at another ARTCC, this was my first midnight shift at my new ARTCC. A foreign air carrier X called but his transmission was unreadable. The same thing happened a few mins later. Finally, on the third attempt I understood him and answered. This time he could not hear me. A few mins later he tried again and we were finally able to communicate. He checked on at FL290, requesting FL330. I checked for traffic and then issued the clearance to climb and maintain FL330 and to report reaching. An aircraft on a different frequency had also been requesting a different altitude, and when I issued the clearance to the foreign carrier to climb, this aircraft asked if it was for him. I advised him that it was for another aircraft and issued the clearance again. I did not notice that the foreign aircraft did not read back the clearance. We are required to manually coordinate the flts that leave our airspace non radar so I coordinated him at FL330. Several mins later the aircraft called and I was sure that he was reporting level at FL330 when he was actually asking if he was cleared to FL330. I answered roger, and to report passing our center boundary. He had some trouble understanding what I was asking, and again asked for FL330. I replied, 'roger, I understand that you are level at FL330,' and again asked him to report the boundary. He said that he would report that point and then said something else that was unreadable. It turned out that he said he was at FL390. Since I did understand that he would report the boundary, and I knew that he was level at FL330, I didn't bother to clarify what was said after that. The aircraft did not report the boundary to me, but checked on with the next center at FL390. They had already descended air carrier Y to FL310 with a pilot's discretion descent to 4000'. This traffic had been informed about the other aircraft and told that he was at FL330. Their traffic was still at FL310 and reported passing over the other aircraft. I couldn't believe it when an arinc message came out reporting my aircraft at FL290. I was so sure in my mind that he had reported level at FL330. I have always prided myself on being able to catch bad readbacks, but it is clear that I need to be even more diligent in the future. I do believe that there are some contributing factors, however. This aircraft was over 300 mi from my closest transmitter and never got closer than 250 mi. The pilot had a very heavy accent and asked if he was cleared to level FL330 instead of using the word request, which might have helped me figure out what he was trying to say. A third factor was that there was not a mode C altitude readout because the aircraft was beyond my radar coverage.

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Original NASA ASRS Text

Title: ARTCC ARTCC INTERFAC COORD WRONG ALT. SYSTEM ERROR.

Narrative: I WAS WORKING A MIDNIGHT SHIFT, AND ALTHOUGH I HAVE BEEN AN FPL FOR OVER 5 YRS AT ANOTHER ARTCC, THIS WAS MY FIRST MIDNIGHT SHIFT AT MY NEW ARTCC. A FOREIGN ACR X CALLED BUT HIS XMISSION WAS UNREADABLE. THE SAME THING HAPPENED A FEW MINS LATER. FINALLY, ON THE THIRD ATTEMPT I UNDERSTOOD HIM AND ANSWERED. THIS TIME HE COULD NOT HEAR ME. A FEW MINS LATER HE TRIED AGAIN AND WE WERE FINALLY ABLE TO COMMUNICATE. HE CHKED ON AT FL290, REQUESTING FL330. I CHKED FOR TFC AND THEN ISSUED THE CLRNC TO CLB AND MAINTAIN FL330 AND TO RPT REACHING. AN ACFT ON A DIFFERENT FREQ HAD ALSO BEEN REQUESTING A DIFFERENT ALT, AND WHEN I ISSUED THE CLRNC TO THE FOREIGN CARRIER TO CLB, THIS ACFT ASKED IF IT WAS FOR HIM. I ADVISED HIM THAT IT WAS FOR ANOTHER ACFT AND ISSUED THE CLRNC AGAIN. I DID NOT NOTICE THAT THE FOREIGN ACFT DID NOT READ BACK THE CLRNC. WE ARE REQUIRED TO MANUALLY COORDINATE THE FLTS THAT LEAVE OUR AIRSPACE NON RADAR SO I COORDINATED HIM AT FL330. SEVERAL MINS LATER THE ACFT CALLED AND I WAS SURE THAT HE WAS REPORTING LEVEL AT FL330 WHEN HE WAS ACTUALLY ASKING IF HE WAS CLRED TO FL330. I ANSWERED ROGER, AND TO RPT PASSING OUR CENTER BOUNDARY. HE HAD SOME TROUBLE UNDERSTANDING WHAT I WAS ASKING, AND AGAIN ASKED FOR FL330. I REPLIED, 'ROGER, I UNDERSTAND THAT YOU ARE LEVEL AT FL330,' AND AGAIN ASKED HIM TO RPT THE BOUNDARY. HE SAID THAT HE WOULD RPT THAT POINT AND THEN SAID SOMETHING ELSE THAT WAS UNREADABLE. IT TURNED OUT THAT HE SAID HE WAS AT FL390. SINCE I DID UNDERSTAND THAT HE WOULD RPT THE BOUNDARY, AND I KNEW THAT HE WAS LEVEL AT FL330, I DIDN'T BOTHER TO CLARIFY WHAT WAS SAID AFTER THAT. THE ACFT DID NOT RPT THE BOUNDARY TO ME, BUT CHKED ON WITH THE NEXT CENTER AT FL390. THEY HAD ALREADY DSNDED ACR Y TO FL310 WITH A PLT'S DISCRETION DSNT TO 4000'. THIS TFC HAD BEEN INFORMED ABOUT THE OTHER ACFT AND TOLD THAT HE WAS AT FL330. THEIR TFC WAS STILL AT FL310 AND RPTED PASSING OVER THE OTHER ACFT. I COULDN'T BELIEVE IT WHEN AN ARINC MESSAGE CAME OUT RPTING MY ACFT AT FL290. I WAS SO SURE IN MY MIND THAT HE HAD RPTED LEVEL AT FL330. I HAVE ALWAYS PRIDED MYSELF ON BEING ABLE TO CATCH BAD READBACKS, BUT IT IS CLR THAT I NEED TO BE EVEN MORE DILIGENT IN THE FUTURE. I DO BELIEVE THAT THERE ARE SOME CONTRIBUTING FACTORS, HOWEVER. THIS ACFT WAS OVER 300 MI FROM MY CLOSEST XMITTER AND NEVER GOT CLOSER THAN 250 MI. THE PLT HAD A VERY HEAVY ACCENT AND ASKED IF HE WAS CLRED TO LEVEL FL330 INSTEAD OF USING THE WORD REQUEST, WHICH MIGHT HAVE HELPED ME FIGURE OUT WHAT HE WAS TRYING TO SAY. A THIRD FACTOR WAS THAT THERE WAS NOT A MODE C ALT READOUT BECAUSE THE ACFT WAS BEYOND MY RADAR COVERAGE.

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.