Narrative:

I entered the southbound bravo surface transition at sfo along highway 101 for san carlos (sql). I knew that sql tower closes normally at xa pm local and that staffing has been very limited due to [company] under staffing. The tower recently was forced to close on certain days at XA45 pm and pattern work is rarely approved. I had checked for notams for a closure on the [date] and hadn't found one during preflight.along the transition I picked up san carlos information tango which indicated that the airport was open and the runway in use.unbeknown to me; as I was still with sfo tower; sql tower announced 'attention all aircraft san carlos tower will be closing in five minutes.'two minutes later; I was told by sfo tower to contact san carlos tower; keep the code. I changed to 119.0 and called 'san carlos tower [call sign]; southbound transition; inbound; full stop; tango' and received no reply. I called 2 more times while turning evasively to avoid the delta and tried calling on communication 2 as well.I considered that I could ask sfo tower; but they were busy with managing their surfaces. I considered contacting nct approach. As it was night and I saw no traffic at the airport or in the vicinity visually or on ads-B and none was called out to me by sfo tower and I knew that the tower staffing was constrained and may have gone home early; I elected to continue predictably on the normal path (overhead midfield 1200; enter right downwind 30) with CTAF calls; while looking for light gun signals; landing just after the normal tower closure time.I'm concerned that:- sql tower closed before their published closure time (announcing 5 minutes at 7 minutes til the hour).- clearly left their position 2 minutes after their '5 minutes' call; leaving the airport unattended while technically still controlled.- failed to communicate this with nearby controllers.in retrospect; I should have orbited outside of the delta for a few minutes and waited until I was certain the airspace was no longer controlled and then entered.I am concerned that the chronic strain on the controllers at san carlos is leading to errors and shortcuts that will cause an accident.

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Original NASA ASRS Text

Title: GA pilot reported confusion when SQL Tower controllers closed Tower Control earlier than NOTAMed due to Controller Staffing.

Narrative: I entered the southbound Bravo surface transition at SFO along Highway 101 for San Carlos (SQL). I knew that SQL tower closes normally at XA pm local and that staffing has been very limited due to [Company] under staffing. The Tower recently was forced to close on certain days at XA45 pm and pattern work is rarely approved. I had checked for NOTAMs for a closure on the [date] and hadn't found one during preflight.Along the transition I picked up San Carlos information Tango which indicated that the airport was open and the runway in use.Unbeknown to me; as I was still with SFO Tower; SQL Tower announced 'Attention all aircraft San Carlos tower will be closing in five minutes.'Two minutes later; I was told by SFO Tower to contact San Carlos Tower; keep the code. I changed to 119.0 and called 'San Carlos Tower [call sign]; southbound transition; inbound; full stop; tango' and received no reply. I called 2 more times while turning evasively to avoid the Delta and tried calling on COM 2 as well.I considered that I could ask SFO Tower; but they were busy with managing their surfaces. I considered contacting NCT approach. As it was night and I saw no traffic at the airport or in the vicinity visually or on ADS-B and none was called out to me by SFO Tower and I knew that the Tower staffing was constrained and may have gone home early; I elected to continue predictably on the normal path (overhead midfield 1200; enter right downwind 30) with CTAF calls; while looking for light gun signals; landing just after the normal Tower closure time.I'm concerned that:- SQL Tower closed before their published closure time (announcing 5 minutes at 7 minutes til the hour).- Clearly left their position 2 minutes after their '5 minutes' call; leaving the airport unattended while technically still controlled.- Failed to communicate this with nearby controllers.In retrospect; I should have orbited outside of the Delta for a few minutes and waited until I was certain the airspace was no longer controlled and then entered.I am concerned that the chronic strain on the controllers at San Carlos is leading to errors and shortcuts that will cause an accident.

Data retrieved from NASA's ASRS site 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.