Narrative:

We were cruising at FL330, tracking directly to ukw as assigned by ATC, with myself as the PF. At approximately 110 NM west of ukw, we received clearance to cross 40 NM west of ukw at FL240, transition to 300 KIAS, and to begin our descent now. At this time my first officer was making the descent PA, so I read back the clearance, then began the descent to FL240. After establishing the descent, I then dialed in the desired 300 KT airspeed, but elected not to select it, since we were indicating 40 KTS less than the 300 KIAS changeover speed. My intention was to make the speed selection at the mach/IAS changeover altitude. When the first officer returned, I advised him that we were descending to cross 40 NM west of ukw at FL240, and transition to 300 KIAS. As we passed through FL280, I allowed myself to be drawn into conversation with our jump seat rider. The distraction led me to miss the mach/IAS changeover, and the aircraft subsequently leveled off at the selected mach .764. At this point we were approximately 55 NM west of ukw. As we leveled off, I realized that we were still in mach mode. I selected IAS on the autoplt, and at the same time ATC inquired about our airspeed. The first officer responded that our airspeed was 325 KIAS. ATC then reiterated the previous airspeed instructions, and we immediately complied.

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Original NASA ASRS Text

Title: SPD DEV NEAR BOWIE, TX.

Narrative: WE WERE CRUISING AT FL330, TRACKING DIRECTLY TO UKW AS ASSIGNED BY ATC, WITH MYSELF AS THE PF. AT APPROX 110 NM W OF UKW, WE RECEIVED CLRNC TO CROSS 40 NM W OF UKW AT FL240, TRANSITION TO 300 KIAS, AND TO BEGIN OUR DSCNT NOW. AT THIS TIME MY FO WAS MAKING THE DSCNT PA, SO I READ BACK THE CLRNC, THEN BEGAN THE DSCNT TO FL240. AFTER ESTABLISHING THE DSCNT, I THEN DIALED IN THE DESIRED 300 KT AIRSPD, BUT ELECTED NOT TO SELECT IT, SINCE WE WERE INDICATING 40 KTS LESS THAN THE 300 KIAS CHANGEOVER SPD. MY INTENTION WAS TO MAKE THE SPD SELECTION AT THE MACH/IAS CHANGEOVER ALT. WHEN THE FO RETURNED, I ADVISED HIM THAT WE WERE DSNDING TO CROSS 40 NM W OF UKW AT FL240, AND TRANSITION TO 300 KIAS. AS WE PASSED THROUGH FL280, I ALLOWED MYSELF TO BE DRAWN INTO CONVERSATION WITH OUR JUMP SEAT RIDER. THE DISTR LED ME TO MISS THE MACH/IAS CHANGEOVER, AND THE ACFT SUBSEQUENTLY LEVELED OFF AT THE SELECTED MACH .764. AT THIS POINT WE WERE APPROX 55 NM W OF UKW. AS WE LEVELED OFF, I REALIZED THAT WE WERE STILL IN MACH MODE. I SELECTED IAS ON THE AUTOPLT, AND AT THE SAME TIME ATC INQUIRED ABOUT OUR AIRSPD. THE FO RESPONDED THAT OUR AIRSPD WAS 325 KIAS. ATC THEN REITERATED THE PREVIOUS AIRSPD INSTRUCTIONS, AND WE IMMEDIATELY COMPLIED.

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.