Narrative:

We were cleared the lander one arrival into denver international. At approximately 30 DME to dvv VOR we were cleared direct den VOR and was being stepped down in 1000 ft increments. At approximately 7 DME and at 12000 ft to den VOR we were cleared left turn 180 degrees and descend to 10000 ft. My first officer made the turn and I selected 10000 ft in the altitude alerter and we both pointed to it and agreed 10000 ft. Passing 10500 ft approach asked our altitude. I responded 10500 ft for 10000 ft. The controller stated maintain 11000 ft. We leveled and began a climb. I questioned him saying 'you cleared us to 10000 ft.' he exclaimed no I didn't. 3 seconds later he said disregard descent and maintain 10000 ft and contact approach 123.85. We had uneventful ILS and ldng into denver. On departure of our 4TH leg of the day we were asked to call the TRACON. The controller supervisor explained that we were cleared to 11000 ft on the audio tapes and that we had penetrated tower's airspace. I asked her how this could happen. She gave me a new understanding of class B airspace. There were many things that contributed to this incident. First: on the day before we timed out with 16 hours of duty, then repositioned the aircraft 2 hours to our overnight in saf. Second: we accepted reduced rest (by invite of the company). Third: we hadn't eaten since late the previous night. Fourth: I'm a new captain of 3 months and new first officer of 6 months. Fifth: we were running 1 hour late due to bad WX in den and trying to catch up. Sixth: shooting multiple approachs to minimums from the start of the previous day until the time of incident. Things I feel could help prevent this in the future. First: don't accept or eliminate from the FARS reduced rest. Second: I will make time to eat in the future. Third: if this airspace has a problem hold all traffic to 12000 ft MSL until clear of tower's airspace due to the audible confusion of 11000 ft and 10000 ft. Supplemental information from acn 391107: the most important factor and possibly the remedy to avoiding this situation from occurring again is the annunciation of 10000 or 11000 ft. 'One zero thousand' and 'one one thousand' or even 'ten thousand' and eleven thousand' spoken over the radio are often misinterpreted. I noticed in other tracons (abq) the controllers annunciate 'one-one thousand- eleven thousand' or 'one zero thousand-ten thousand' to clarify the assigned altitude. This should be common practice at all tracons.

Related reports:

Google
 

Original NASA ASRS Text

Title: BE1900D ACFT ON ARR ROUTING, FLC HEARS CLRNC TO 10000 FT AND WHEN PASSING 10600 FT ATC INTERVENES AND TELLS THEM THEY WERE ONLY CLRED TO 11000 FT.

Narrative: WE WERE CLRED THE LANDER ONE ARR INTO DENVER INTL. AT APPROX 30 DME TO DVV VOR WE WERE CLRED DIRECT DEN VOR AND WAS BEING STEPPED DOWN IN 1000 FT INCREMENTS. AT APPROX 7 DME AND AT 12000 FT TO DEN VOR WE WERE CLRED L TURN 180 DEGS AND DSND TO 10000 FT. MY FO MADE THE TURN AND I SELECTED 10000 FT IN THE ALT ALERTER AND WE BOTH POINTED TO IT AND AGREED 10000 FT. PASSING 10500 FT APCH ASKED OUR ALT. I RESPONDED 10500 FT FOR 10000 FT. THE CTLR STATED MAINTAIN 11000 FT. WE LEVELED AND BEGAN A CLB. I QUESTIONED HIM SAYING 'YOU CLRED US TO 10000 FT.' HE EXCLAIMED NO I DIDN'T. 3 SECONDS LATER HE SAID DISREGARD DSCNT AND MAINTAIN 10000 FT AND CONTACT APCH 123.85. WE HAD UNEVENTFUL ILS AND LDNG INTO DENVER. ON DEP OF OUR 4TH LEG OF THE DAY WE WERE ASKED TO CALL THE TRACON. THE CTLR SUPVR EXPLAINED THAT WE WERE CLRED TO 11000 FT ON THE AUDIO TAPES AND THAT WE HAD PENETRATED TWR'S AIRSPACE. I ASKED HER HOW THIS COULD HAPPEN. SHE GAVE ME A NEW UNDERSTANDING OF CLASS B AIRSPACE. THERE WERE MANY THINGS THAT CONTRIBUTED TO THIS INCIDENT. FIRST: ON THE DAY BEFORE WE TIMED OUT WITH 16 HRS OF DUTY, THEN REPOSITIONED THE ACFT 2 HRS TO OUR OVERNIGHT IN SAF. SECOND: WE ACCEPTED REDUCED REST (BY INVITE OF THE COMPANY). THIRD: WE HADN'T EATEN SINCE LATE THE PREVIOUS NIGHT. FOURTH: I'M A NEW CAPT OF 3 MONTHS AND NEW FO OF 6 MONTHS. FIFTH: WE WERE RUNNING 1 HR LATE DUE TO BAD WX IN DEN AND TRYING TO CATCH UP. SIXTH: SHOOTING MULTIPLE APCHS TO MINIMUMS FROM THE START OF THE PREVIOUS DAY UNTIL THE TIME OF INCIDENT. THINGS I FEEL COULD HELP PREVENT THIS IN THE FUTURE. FIRST: DON'T ACCEPT OR ELIMINATE FROM THE FARS REDUCED REST. SECOND: I WILL MAKE TIME TO EAT IN THE FUTURE. THIRD: IF THIS AIRSPACE HAS A PROB HOLD ALL TFC TO 12000 FT MSL UNTIL CLR OF TWR'S AIRSPACE DUE TO THE AUDIBLE CONFUSION OF 11000 FT AND 10000 FT. SUPPLEMENTAL INFO FROM ACN 391107: THE MOST IMPORTANT FACTOR AND POSSIBLY THE REMEDY TO AVOIDING THIS SIT FROM OCCURRING AGAIN IS THE ANNUNCIATION OF 10000 OR 11000 FT. 'ONE ZERO THOUSAND' AND 'ONE ONE THOUSAND' OR EVEN 'TEN THOUSAND' AND ELEVEN THOUSAND' SPOKEN OVER THE RADIO ARE OFTEN MISINTERPRETED. I NOTICED IN OTHER TRACONS (ABQ) THE CTLRS ANNUNCIATE 'ONE-ONE THOUSAND- ELEVEN THOUSAND' OR 'ONE ZERO THOUSAND-TEN THOUSAND' TO CLARIFY THE ASSIGNED ALT. THIS SHOULD BE COMMON PRACTICE AT ALL TRACONS.

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.