Narrative:

We had requested climb clearance from FL2380 to FL390 and were given a turn to the right off course for a climb vector and then clearance to what we understood was the requested altitude, FL390. While climbing through FL300 ATC informed us of a possible altitude excursion and to descend to and maintain FL290, which we did. We advised ATC we had requested FL390, had understood we had been cleared to FL390 and had acknowledged that altitude on readback. Believing that, we had inserted 39000' in our flight director/altitude alert window as well. At the same time as ATC warning we got a TCAS 2 second RA of, 'slow climb rate,' followed immediately by a 'clear of traffic.' we later found that conflicting traffic passed 2 mi behind us. ATC gave no traffic information. If in fact ATC is correct (which I don't know at this time), then both pilots misheard the clearance as FL390. Having set 39000' in the window, I can't imagine why we would acknowledge anything else. In reviewing the incident afterward with my copilot we both agreed that FL390 was what we clearly heard and acknowledged. If this is a case of hearing what you expect to hear for a clearance, then it's a very graphic, scary. First time example for me. Perhaps different terminology is needed to shake possible mindset if that's what it was (e.g., cleared to FL290 only, not FL390 as requested) because there was no grey area for us. We never heard FL290 mentioned, as we remember it, until ATC asked us to descend there. This is probably a good reason for retaining 3-M cockpits!

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Original NASA ASRS Text

Title: FLT CREW UNDERSTOOD CLIMB FL390. AT FL300 CTLR ADVISED HAD BEEN CLEARED ONLY TO FL290.

Narrative: WE HAD REQUESTED CLB CLRNC FROM FL2380 TO FL390 AND WERE GIVEN A TURN TO THE RIGHT OFF COURSE FOR A CLB VECTOR AND THEN CLRNC TO WHAT WE UNDERSTOOD WAS THE REQUESTED ALT, FL390. WHILE CLBING THROUGH FL300 ATC INFORMED US OF A POSSIBLE ALT EXCURSION AND TO DSND TO AND MAINTAIN FL290, WHICH WE DID. WE ADVISED ATC WE HAD REQUESTED FL390, HAD UNDERSTOOD WE HAD BEEN CLRED TO FL390 AND HAD ACKNOWLEDGED THAT ALT ON READBACK. BELIEVING THAT, WE HAD INSERTED 39000' IN OUR FLT DIRECTOR/ALT ALERT WINDOW AS WELL. AT THE SAME TIME AS ATC WARNING WE GOT A TCAS 2 SEC RA OF, 'SLOW CLB RATE,' FOLLOWED IMMEDIATELY BY A 'CLR OF TFC.' WE LATER FOUND THAT CONFLICTING TFC PASSED 2 MI BEHIND US. ATC GAVE NO TFC INFO. IF IN FACT ATC IS CORRECT (WHICH I DON'T KNOW AT THIS TIME), THEN BOTH PLTS MISHEARD THE CLRNC AS FL390. HAVING SET 39000' IN THE WINDOW, I CAN'T IMAGINE WHY WE WOULD ACKNOWLEDGE ANYTHING ELSE. IN REVIEWING THE INCIDENT AFTERWARD WITH MY COPLT WE BOTH AGREED THAT FL390 WAS WHAT WE CLEARLY HEARD AND ACKNOWLEDGED. IF THIS IS A CASE OF HEARING WHAT YOU EXPECT TO HEAR FOR A CLRNC, THEN IT'S A VERY GRAPHIC, SCARY. FIRST TIME EXAMPLE FOR ME. PERHAPS DIFFERENT TERMINOLOGY IS NEEDED TO SHAKE POSSIBLE MINDSET IF THAT'S WHAT IT WAS (E.G., CLRED TO FL290 ONLY, NOT FL390 AS REQUESTED) BECAUSE THERE WAS NO GREY AREA FOR US. WE NEVER HEARD FL290 MENTIONED, AS WE REMEMBER IT, UNTIL ATC ASKED US TO DSND THERE. THIS IS PROBABLY A GOOD REASON FOR RETAINING 3-M COCKPITS!

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.