Small Aircraft; High Wing; 1 Eng; Fixed Gear
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Flight Instructor; Flight Crew Commercial
Flight Crew Last 90 Days 100; Flight Crew Total 2000; Flight Crew Type 1500
Confusion; Situational Awareness; Workload; Communication Breakdown
ATC Issue All Types; Airspace Violation All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Requested ATC Assistance / Clarification
Procedure; Human Factors; Airspace Structure
I was on a San Francisco Bay Tour with a student for their first discovery flight.  I departed having arranged for a transponder code and Oakland Class C transition prior to departure.  Having transited through Oakland tower; I was instructed to contact Northern California (Norcal) Approach on 120.90.  Remaining within two-way communication throughout the entire event; we completed our flight over the Bay and asked Norcal for an Oakland transition; landing ZZZ with the current ATIS.  Norcal replied that our transition was approved; altitude at our discretion. Norcal was busy with other aircraft requests on frequency and did not issue our hand-off until we were almost abeam the Oakland Coliseum.  After the hand-off Oakland tower asked when I received my transfer; to which I replied I had just received it and made immediate contact. The controller then told me that I needed to establish two-way communication prior to entry in his area; which I had because I was talking to Norcal. I replied that Norcal was inundated with many pilot requests and I didn't have opportunity to make request for the hand-off earlier.  I feel that my actions were in compliance with the regulations; I was using a discreet transponder code; was in two-way communications at all times with the various controlling agencies. Perhaps if Norcal amended the instructions to include handoff instructions at a certain point; it could minimize workload in the event that the frequency congestion takes place.  Example; 'transition approved as requested; contact Oakland tower upon crossing Lake Merritt.'
An instructor with student completed an introductory SFO Bay tour and when returning to the airport did not receive a NCT to OAK handoff until abeam the Oakland Coliseum. OAK Tower wanted information about the late communications handoff.