King Air C90 E90
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Flight Instructor; Flight Crew Commercial
Flight Crew Last 90 Days 132; Flight Crew Total 1265; Flight Crew Type 14
Situational Awareness
Airspace Violation All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert
Human Factors; Airspace Structure
We were receiving VFR flight following during a non-revenue; part 91 leg into PAO. Approximately 5 miles east of the field; as we were flying direct to a 3 mile final for runway 31 at PAO; NorCal TRACON terminated radar services and approved us to change frequencies to advisory; since the Palo Alto tower was closed. We changed our squawk code to 1200 and changed frequencies to CTAF; immediately broadcasting our position and intention to enter a 3 mile right base for runway 31. Shortly thereafter; a Bonanza came on frequency and announced a 6 mile final for 31. We broadcast that we were about to turn a 3 mile final approach and the Bonanza agreed that we would be first for the field. While in the turn to final; Moffett tower (NUQ) transmitted on Palo Alto CTAF and stated that Moffett tower was in operation and there were two aircraft in the Moffett class D without coordination. We rolled out on final and landed without incident; but after landing reviewed the San Francisco terminal area chart (TAC) and determined that we (along with the Bonanza) were likely one of the aircraft the tower was referring to. Our approach and arrival profile was not unusual for both IFR (visual) and VFR arrivals into PAO. Having never encountered issues before; we did not review the TAC prior to or in flight for possible airspace conflicts. Additionally; since we had been flying direct to that 3 mile final for over 100 miles and receiving flight following; we mistakenly assumed that ATC would have coordinated for us if necessary or advised us of a conflict ahead in the last 5 miles of the flight. After reviewing the TAC; it became clear that for the 2 hours when Palo Alto tower is closed but Moffett's is open; the only way to enter the pattern for runway 31 from the east without flying through the northwest portion of the NUQ class D is to fly essentially to midfield at PAO and turn a tight base out of the right downwind; as anything past approximately a 1 mile final for 31 is in the NUQ class D. Other options would be to explicitly ask TRACON for coordination; or to call Moffett tower immediately after handoff and request a class D transition. This was a good reminder of the insidious nature of complacency - making a VFR approach; we were certainly aware of the limits of the SFO class B and SJC class C and briefed the class B altitudes and our speed limits; but once cleared through or clear of both of those; our entire focus was on entering the pattern at PAO; not the adjoining airports. It was a good reminder that even though VFR flight is generally perceived to have fewer restrictions than IFR; it comes with an increased burden of preparation and situational awareness on the pilot's part when it comes to airspace.
BE90 reported an airspace violation on approach to PAO; citing the unusual airspace structure relative to NUQ as contributing to the event.