Narrative:

On arrival into the stl area, we were told to expect runway 30R. Soon after, they assigned runway 24, which would allow for an earlier arrival. We were assigned 5000 ft and given a heading to join the runway 24 localizer. We called the field in sight about 25 mi out. At that point I notified my first officer that I would be off at communication #1 to notify our company that we were in range on communication #2. In that period, we were cleared to 3500 ft. Shortly thereafter, we were cleared for the visual approach to runway 24. When cleared to 3500 ft, my first officer started his descent right away. During the descent, we were below class B airspace for a few moments, which I had not realized until after the fact. Hence, we may have exceeded the 200 KT restr below class B airspace. However, ATC did not mention anything pertaining to the matter. Contributing factors were: allowing myself to be distraction with an unnecessary (at the time) radio call to company, letting my guard down during a clear VFR day visual approach, and my first officer's low experience (it was his first week off of IOE). Also, I am confused on why ATC would give a clearance to an altitude which would put you below class B airspace at all! If so, they should give a warning or advisory.

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Original NASA ASRS Text

Title: BA32 DSNDS OUTSIDE OF T75 CLASS B AIRSPACE WHEN CLRED FROM ILS TO VISUAL APCH. PLT CONCERNED WITH ATC RECOGNITION OF SIT.

Narrative: ON ARR INTO THE STL AREA, WE WERE TOLD TO EXPECT RWY 30R. SOON AFTER, THEY ASSIGNED RWY 24, WHICH WOULD ALLOW FOR AN EARLIER ARR. WE WERE ASSIGNED 5000 FT AND GIVEN A HDG TO JOIN THE RWY 24 LOC. WE CALLED THE FIELD IN SIGHT ABOUT 25 MI OUT. AT THAT POINT I NOTIFIED MY FO THAT I WOULD BE OFF AT COM #1 TO NOTIFY OUR COMPANY THAT WE WERE IN RANGE ON COM #2. IN THAT PERIOD, WE WERE CLRED TO 3500 FT. SHORTLY THEREAFTER, WE WERE CLRED FOR THE VISUAL APCH TO RWY 24. WHEN CLRED TO 3500 FT, MY FO STARTED HIS DSCNT RIGHT AWAY. DURING THE DSCNT, WE WERE BELOW CLASS B AIRSPACE FOR A FEW MOMENTS, WHICH I HAD NOT REALIZED UNTIL AFTER THE FACT. HENCE, WE MAY HAVE EXCEEDED THE 200 KT RESTR BELOW CLASS B AIRSPACE. HOWEVER, ATC DID NOT MENTION ANYTHING PERTAINING TO THE MATTER. CONTRIBUTING FACTORS WERE: ALLOWING MYSELF TO BE DISTR WITH AN UNNECESSARY (AT THE TIME) RADIO CALL TO COMPANY, LETTING MY GUARD DOWN DURING A CLR VFR DAY VISUAL APCH, AND MY FO'S LOW EXPERIENCE (IT WAS HIS FIRST WK OFF OF IOE). ALSO, I AM CONFUSED ON WHY ATC WOULD GIVE A CLRNC TO AN ALT WHICH WOULD PUT YOU BELOW CLASS B AIRSPACE AT ALL! IF SO, THEY SHOULD GIVE A WARNING OR ADVISORY.

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.