Narrative:

The incident occurred on the third day of a 3 day trip. Today's flight started from pdk at AM00Z with a destination of stp. I was in the left seat and the PNF. The first officer was flying the aircraft. We were flying the kaspr 2 arrival to stp and had been cleared to 11000 ft. The altitude alerter was preset to 11000 ft as per our operations manual: PNF receives and confirms the new altitude with ATC. PF repeats the newly assigned altitude. After PF and PNF agree on the new altitude, the PNF sets the altitude into the altitude alerter. PNF states altitude is set. This procedure has been in our operations for over 10 yrs and was developed due to the occurrence of 2 altitude excursions within a relatively short period. During the descent, at approximately 14000 ft, the PF questioned the assigned altitude. I stated 11000 ft. At approximately 11500 ft ATC questioned our altitude. I responded our current altitude whereby ATC informed us that our clearance was to 12000 ft! The next event, which occurred within seconds of ATC's last call, was a TCASII resolution which the PF executed by climbing. I informed ATC of the resolution and our maneuver. After maneuvering to meet the TCASII resolution our aircraft was leveled at 12000 ft. We then proceeded to stp. I believe that I understood the clearance correctly and ATC made an error. Yet after reviewing the flight with the first officer I know the incident could have been avoided. The first officer being unsure of the assigned altitude is the key since it raised the flag of doubt. Once I stated 11000 ft was the assigned altitude, the first officer's doubt was removed. He should have asked for clarification. Even so, I should have asked ATC to confirm the assigned altitude. This action would have removed all doubt. Through experience I have learned when there is doubt concerning an ATC clearance that a confirmation should be obtained. Unfortunately, I did not confirm the clearance. In the chain of events leading to this incident I had the opportunity to break the chain. Did ATC clear us to descend to 12000 ft or 11000 ft? Did I read back the clearance wrong? Did ATC acknowledge an incorrect readback? Did ATC clear us to 11000 ft meaning 12000 ft? Did the first officer hear ATC's clearance or was he responding to my readback? The issues are all valid concerns, but in reality only philosophical questions. The bottom line: I had the responsibility and opportunity to correct and avoid the situation when the PF raised a concern. Lesson learned: always reconfirm an ATC clearance even though 1 crew member is 110% sure. As long as 1 crew member is less than 100% sure, an ATC clearance must be confirmed.

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Original NASA ASRS Text

Title: A DSNDING FALCON 2000 OVERSHOT ITS ASSIGNED ALT WHEN THE CREW HAD A CLRNC INTERP PROB AND A BREAKDOWN IN THE CRM AS DESIGNED BY THEIR OPS DEPT. NMAC OCCURRED WITH COMMUTER ACFT BELOW.

Narrative: THE INCIDENT OCCURRED ON THE THIRD DAY OF A 3 DAY TRIP. TODAY'S FLT STARTED FROM PDK AT AM00Z WITH A DEST OF STP. I WAS IN THE L SEAT AND THE PNF. THE FO WAS FLYING THE ACFT. WE WERE FLYING THE KASPR 2 ARR TO STP AND HAD BEEN CLRED TO 11000 FT. THE ALT ALERTER WAS PRESET TO 11000 FT AS PER OUR OPS MANUAL: PNF RECEIVES AND CONFIRMS THE NEW ALT WITH ATC. PF REPEATS THE NEWLY ASSIGNED ALT. AFTER PF AND PNF AGREE ON THE NEW ALT, THE PNF SETS THE ALT INTO THE ALT ALERTER. PNF STATES ALT IS SET. THIS PROC HAS BEEN IN OUR OPS FOR OVER 10 YRS AND WAS DEVELOPED DUE TO THE OCCURRENCE OF 2 ALT EXCURSIONS WITHIN A RELATIVELY SHORT PERIOD. DURING THE DSCNT, AT APPROX 14000 FT, THE PF QUESTIONED THE ASSIGNED ALT. I STATED 11000 FT. AT APPROX 11500 FT ATC QUESTIONED OUR ALT. I RESPONDED OUR CURRENT ALT WHEREBY ATC INFORMED US THAT OUR CLRNC WAS TO 12000 FT! THE NEXT EVENT, WHICH OCCURRED WITHIN SECONDS OF ATC'S LAST CALL, WAS A TCASII RESOLUTION WHICH THE PF EXECUTED BY CLBING. I INFORMED ATC OF THE RESOLUTION AND OUR MANEUVER. AFTER MANEUVERING TO MEET THE TCASII RESOLUTION OUR ACFT WAS LEVELED AT 12000 FT. WE THEN PROCEEDED TO STP. I BELIEVE THAT I UNDERSTOOD THE CLRNC CORRECTLY AND ATC MADE AN ERROR. YET AFTER REVIEWING THE FLT WITH THE FO I KNOW THE INCIDENT COULD HAVE BEEN AVOIDED. THE FO BEING UNSURE OF THE ASSIGNED ALT IS THE KEY SINCE IT RAISED THE FLAG OF DOUBT. ONCE I STATED 11000 FT WAS THE ASSIGNED ALT, THE FO'S DOUBT WAS REMOVED. HE SHOULD HAVE ASKED FOR CLARIFICATION. EVEN SO, I SHOULD HAVE ASKED ATC TO CONFIRM THE ASSIGNED ALT. THIS ACTION WOULD HAVE REMOVED ALL DOUBT. THROUGH EXPERIENCE I HAVE LEARNED WHEN THERE IS DOUBT CONCERNING AN ATC CLRNC THAT A CONFIRMATION SHOULD BE OBTAINED. UNFORTUNATELY, I DID NOT CONFIRM THE CLRNC. IN THE CHAIN OF EVENTS LEADING TO THIS INCIDENT I HAD THE OPPORTUNITY TO BREAK THE CHAIN. DID ATC CLR US TO DSND TO 12000 FT OR 11000 FT? DID I READ BACK THE CLRNC WRONG? DID ATC ACKNOWLEDGE AN INCORRECT READBACK? DID ATC CLR US TO 11000 FT MEANING 12000 FT? DID THE FO HEAR ATC'S CLRNC OR WAS HE RESPONDING TO MY READBACK? THE ISSUES ARE ALL VALID CONCERNS, BUT IN REALITY ONLY PHILOSOPHICAL QUESTIONS. THE BOTTOM LINE: I HAD THE RESPONSIBILITY AND OPPORTUNITY TO CORRECT AND AVOID THE SIT WHEN THE PF RAISED A CONCERN. LESSON LEARNED: ALWAYS RECONFIRM AN ATC CLRNC EVEN THOUGH 1 CREW MEMBER IS 110% SURE. AS LONG AS 1 CREW MEMBER IS LESS THAN 100% SURE, AN ATC CLRNC MUST BE CONFIRMED.

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.