Narrative:

Departed incheon runway 33L on the nopik 1A departure. Departure control cleared us direct hanky, fpr. We were directed to contact incheon control on frequency 122.4. Incheon control cleared us to climb and maintain FL390. The captain read back 'climb and maintain FL390' and I confirmed 'FL390.' passing FL360, about 10 DME before botki intersection on B576, the controller that cleared us to FL390 asked us to verify climbing to FL350. The captain told her that she cleared us to FL390 but we would descend to FL350. We started back down at about FL365. Upon reaching FL350, the captain reported level at FL350. She said 'roger and maintain FL390.' the captain asked her to confirm whether she wanted us at FL350 or FL390. A male controller came on and asked us to maintain FL350. The captain told him that this was the second time we were cleared to FL390. He said 'roger, maintain FL350.' another aircraft on the same frequency was asked by the same controller to verify climbing to FL150. He thought he was cleared to FL190. This controller seems to confuse the number '5' and '9.'

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Original NASA ASRS Text

Title: ACR ACFT CLBING OUT FROM SEOUL, KOREA, HAS DIFFICULTY WITH ATC'S PRONUNCIATION OF 5 VERSUS 9 DURING ALT ASSIGNMENT.

Narrative: DEPARTED INCHEON RWY 33L ON THE NOPIK 1A DEP. DEP CTL CLRED US DIRECT HANKY, FPR. WE WERE DIRECTED TO CONTACT INCHEON CTL ON FREQ 122.4. INCHEON CTL CLRED US TO CLB AND MAINTAIN FL390. THE CAPT READ BACK 'CLB AND MAINTAIN FL390' AND I CONFIRMED 'FL390.' PASSING FL360, ABOUT 10 DME BEFORE BOTKI INTXN ON B576, THE CTLR THAT CLRED US TO FL390 ASKED US TO VERIFY CLBING TO FL350. THE CAPT TOLD HER THAT SHE CLRED US TO FL390 BUT WE WOULD DSND TO FL350. WE STARTED BACK DOWN AT ABOUT FL365. UPON REACHING FL350, THE CAPT RPTED LEVEL AT FL350. SHE SAID 'ROGER AND MAINTAIN FL390.' THE CAPT ASKED HER TO CONFIRM WHETHER SHE WANTED US AT FL350 OR FL390. A MALE CTLR CAME ON AND ASKED US TO MAINTAIN FL350. THE CAPT TOLD HIM THAT THIS WAS THE SECOND TIME WE WERE CLRED TO FL390. HE SAID 'ROGER, MAINTAIN FL350.' ANOTHER ACFT ON THE SAME FREQ WAS ASKED BY THE SAME CTLR TO VERIFY CLBING TO FL150. HE THOUGHT HE WAS CLRED TO FL190. THIS CTLR SEEMS TO CONFUSE THE NUMBER '5' AND '9.'

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.