B737-700
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 401
Distraction; Situational Awareness
ATC Issue All Types; Deviation - Altitude Overshoot; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification
Airspace Structure; Chart Or Publication; Company Policy; Human Factors; Procedure
We were descending to 6;000 feet on the RNAV Arrival. During the descent; we got cleared to an intersection and to cross it at 3;000 feet. The First Officer selected 3;000 feet and hit LVL CHG. We then got cleared for the RNAV Approach. He verified 3;000 feet in FMC and set 1;500 feet in the altitude selector. ATC also wanted us to maintain 250 knots until advised. I was concerned with Class B airspace and the 210 restriction at a fix; so we discussed the airspeed issue and missed the fact that we were not in VNAV. The aircraft descended below 3;000 feet prior to the fix and ATC asked us about it. We immediately climbed back up to 3;000 feet and crossed the fix to comply with the clearance. We continued the approach with no further issues and landed safely.
B737-700 Captain reported ATC assigned airspeed 250 kts below the ORD Class B airspace on an RNAV arrival into the ORD area.