Medium Large Transport; Low Wing; 2 Turbojet Eng
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Situational Awareness
Deviation - Speed All Types; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Became Reoriented
Human Factors; Airspace Structure
We were filed [on our short route to DCA] which has a filed cruise altitude of 8;000'. Since we were below 10;000'; we were cruising at 245 KIAS. On [approach] we had already been descended down to 4;000'. ATC queried us on our airspeed to which we responded 245 KIAS. The First Officer (Pilot Monitoring) then thought about us cruising below the Class B airspace and exceeding the max speed of 200 KIAS. We pulled up the VFR sectional chart to find out that we were in fact below the Class B shelf at 4;000' for a small quadrant. We then asked ATC if they required a specific speed to which we were told our discretion. By then we were back into the next Class B quadrant which went down to 3;500' and we remained in Class B for the remainder of the flight.The thought of us flying below Class B airspace hadn't occurred to me since that is usually not a factor for us. Once in a while you will hear ATC inform you that you will be exiting the Class B airspace when you are on extended vectors for an approach. That is your reminder that you should slow to 200 KIAS if not already slowed to below that airspeed. That reminder didn't apply in this case since we were still on the cruise portion of our flight. I believe this experience made both crew members more aware of using our resources to their fullest extent. Having the VFR sectional chart open when cruising on these low level escape routes would have identified the different Class B airspace quadrants that we would be encountering during our routine flight.
[Report narrative contained no additional information.]
Air Carrier flight crew reported they inadvertently exceeded the 200 kt airspeed limit operating below the Class B shelf inbound to DCA.