Narrative:

Captain requested clearance from FL330 to FL350 because of light turbulence at FL330. This request was not granted, but I (first officer) thought that it was and proceeded to climb to FL350. Other crewmembers did not notice that I had climbed until taipei control asked us our altitude which was then at FL34.7 (34,700 ft). I then turned off the transponder and descended to FL330 which was our cleared altitude. Taipei control then asked us what altitude we were at and we replied FL330. Taipei controller thought that they had a problem with their radar as well as a problem with our transponder. We let them believe that the problem was theirs. Supplemental information from acn 301533: while cruising at FL330, I requested FL350 from the center. I was told that they were unable to approve FL350 because of opposite direction traffic at FL350, 100 NM ahead of us. I replied 'roger' and forgot about it for the time being. Approximately 4 mins later I noticed that my altimeter read FL350, and realized that the copilot (who was flying the airplane), had misunderstood the ATC denial of our request, and had mistakenly climbed the aircraft to FL350. We immediately descended to FL330 and confirmed to ATC that we were level FL330.

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Original NASA ASRS Text

Title: ALTDEV ALT EXCURSION - THE CAPT REQUESTED A HIGHER ALT, BUT ARTCC REFUSED BECAUSE OF CONFLICTING TFC THEN THE FO CLBED ANYWAY.

Narrative: CAPT REQUESTED CLRNC FROM FL330 TO FL350 BECAUSE OF LIGHT TURB AT FL330. THIS REQUEST WAS NOT GRANTED, BUT I (FO) THOUGHT THAT IT WAS AND PROCEEDED TO CLB TO FL350. OTHER CREWMEMBERS DID NOT NOTICE THAT I HAD CLBED UNTIL TAIPEI CTL ASKED US OUR ALT WHICH WAS THEN AT FL34.7 (34,700 FT). I THEN TURNED OFF THE XPONDER AND DSNDED TO FL330 WHICH WAS OUR CLRED ALT. TAIPEI CTL THEN ASKED US WHAT ALT WE WERE AT AND WE REPLIED FL330. TAIPEI CTLR THOUGHT THAT THEY HAD A PROB WITH THEIR RADAR AS WELL AS A PROB WITH OUR XPONDER. WE LET THEM BELIEVE THAT THE PROB WAS THEIRS. SUPPLEMENTAL INFO FROM ACN 301533: WHILE CRUISING AT FL330, I REQUESTED FL350 FROM THE CTR. I WAS TOLD THAT THEY WERE UNABLE TO APPROVE FL350 BECAUSE OF OPPOSITE DIRECTION TFC AT FL350, 100 NM AHEAD OF US. I REPLIED 'ROGER' AND FORGOT ABOUT IT FOR THE TIME BEING. APPROX 4 MINS LATER I NOTICED THAT MY ALTIMETER READ FL350, AND REALIZED THAT THE COPLT (WHO WAS FLYING THE AIRPLANE), HAD MISUNDERSTOOD THE ATC DENIAL OF OUR REQUEST, AND HAD MISTAKENLY CLBED THE ACFT TO FL350. WE IMMEDIATELY DSNDED TO FL330 AND CONFIRMED TO ATC THAT WE WERE LEVEL FL330.

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.