B737-700
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 108; Flight Crew Type 18300
Situational Awareness
Airspace Violation All Types; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
Human Factors; Airspace Structure
Upon being seated in the hotel van; the van driver showed me a piece of paper with 'MLS Tower' and an area code and phone number and told me that I should call that number. This was the first indication of anything possibly going wrong with our flight. As per Union instruction; I did not call the number. When I arrived at my room; I looked up 'MLS Tower' and found it to be an airport in Montana; so I figured the message re: MLS was probably in error. The more I thought about it the next day; I came to realize that during transition from the SUUTR1 Arrival to the visual approach; it is possible that we transited SAC Exec Airport Class D airspace. NorCal cleared us for visual approach to 34L and I turned slightly to the right around ELMAC toward the FAF (HADSU). At about this time; NorCal issued us a traffic advisory. We did not see any traffic where the controller described visually or on TCAS. We were both busy looking for that traffic as I descended toward the FAF altitude; all the while remaining above the 34L glideslope.It is possible; looking at the airspace later; that we may have inadvertently clipped the edge of SAC Exec Airport Class D airspace; which is a five mile ring up to 2;500 feet. I have been flying into SMF for [many] years; and have never noticed how close that airport is to the arrival corridor to 34L and 34R. It is possible with the fairly recent advent of the SUUTR 1 STAR; that we are being brought closer to the Class D airspace than we were previously when we typically were vectored by NorCal. It is also nearly impossible to tell exactly where the five mile boundary of that Class D is when you are flying the arrival/approach unless you happen to see the airport itself; which we did not.If this is indeed what the 'phone call' was about; we should inform company crews of the need to stay on the LNAV arrival all the way to ELMAC and/or be very careful of the SAC Exec Class D airspace.
B737 Captain believes that he may have passed through SAC Class D airspace during a visual approach to Runway 34L at SMF.